Need help with cooling!

[NewZed]

 

As to "Units are irrelevant":

The thought that a 160F thermostat opens at 160 and is fully opened "10 Degrees  Later" by 170 is WRONG! It is an original 72C open by 82C  (162 to 180F)

This would be either a math or a conversion error.  And the words about when the thermostats are fully opened or closed aren't mine, so the conversion or math error isn't either.  My point is, 100 degrees C means the same things as 212 F, that's what I meant by units are irrelevant. 

 

I understand everything that's been discussed about cooling.  My new, moving-on questions are: what is an engine's optimum operating temperature, and what is the root cause (the physical actions taking place with the fuel) that causes the poor running after heat soak (e.g. bubbles from fuel vaporizing in the lines, fuel vaporizing as it leaves the hot injector tip causing poor metering, sticking injector internals...).  My fan works, your 160 thermostat works.  There is no universal ideal, the method used to avoid heat soak is conditional.  Your method gives up engine coolant temperature control.  You have to choose between running hotter coolant and accepting heat soak as a condition of hotter coolant or solving heat soak and running cooler coolant.  I don't, I can run whatever coolant temperature I want.  I have more freedom of choice with my solution.

 

As far as what people write on the internet, it's nice when you find well-supported writing but the bulk of what's on the internet is placed there by people who like to write, or talk,with no data to support their theories.  Quite often, 90% of what they write is correct, but then there's another 10% of conjecture.  Grain of salt material.

 

Discussion about Oregon's weather and gasoline quality variables are context, for discussion, probably only useful to people who know the weather in Oregon or Arizona or Southern California, and something about gasoline formulating.  At the the center of the issue is what's happening to the gasoline.  It would be foolish to ignore differences in formulation in trying to explain why different people see different results.

 

And just for anyone interested, the main difference between our two styles of discussion is that I start with the assumption that the other party knows what they're talking about and you seem to start with the assumption that they don't.  It has a big affect on how you format your arguments.  My way causes me to go out and learn new supporting data for the other side's case, your way is to take things you already know and use it to attack the other side's case.  You're going over the same ground again and again, with nothing new, and inferring things that aren't true about the person making the other case ("choosing not to observe" - ad hominem), in an attempt to win an argument instead of shed some new light on a subject.

 

 

 

Still interested in pharoahbq's 280Z thermostats, for the record, if the information becomes available in the future.  And, if anyone is interested and wants to take a shot at it, the two questions about optimum engine temperature, and the mechanism behind the hot start problem.

[Pharaohabq]

You can understand I'm sure that I'm not really willing to crack open my 280Z thermo housing when that engine is running fine.  I will certainly check the 260Z and see what temp the Thermostat is set for.  I'me very curious to see that effect the "Tropical" thermo has on the car.  I could hope it's the best fix for the vapor locking issue.  Thanks Tony for that information. I'll start there and later if we still need, we will ask for your buddies info for the PS Cooler repurpose. That sounds fun in any case.

 

As for the Optimum Engine Temperature, I would expect it should have to do with the temperature your oil is designed to best lubricate. 

 

From a Fuel perspective, A hotter engine sounds logical, colder air mixed in the right ratio with fuel expands a certain amount. Hotter combustion equals more expansion from ambient. Running too cold won't really hurt anything in our engines, though I'd expect lower MPG, but it's probably negligable.  Too hot and we have what this thread is about.  I've never studied what the optimal fuel inlet temp should be, but just like air, I'd bet it's better cooler than hotter. No but that's combustion, not the actual engine temperature.

 

 The ECU in modern cars automatically adjusts the A/F ratio based on engine temperature / air temperature to try to keep that same AFR of~13:1 all the time.  So I'm sure there's arguements for hotter/colder running engines, but you'd have to look at the fuel's properties to be able to say what's ideal.  For our cars, there's no O2 sensor or MAP Sensor so the ECU isn't trying to keep the engine ideally running, the S30 ECU is only timing injector pulses and reading the "percieved" airflow from the AFM (percieved since it can't tell the air density) to adjust the mixture so our cars will run in most conditions, but never most consistantly ideal due to that same disregard for air density.

 

Upgraded to modern EFI (batch like Megasquirt, or other MPI MAP based) allows our engines not only to run as designed, but to also run efficiently at the right A/F ratio.  Engine Temp affects the intake air temp and may cause a change in the ideal A/F required, but it's not the Engine temp that's most important, aside from keeping it from blowing up, it's the intake air temp and fuel ratio that needs to be ideal as adjusted by the modern ECU.

 

So as for actual block temp, I'd say it's lubrication dependant, aside from materials limitations such as hardness of your rings etc, since the EFI system is going to run according to it's design, which Tony noted earlier can vary.

[78zstyle]

Changing the thermostat won't fix the vapor locking issue, as it happens when the engine is not running, therefor no coolant is flowing. The issue happens when the engine is off and sits for a bit.

[NewZed]

How hot everything is when you shut the engine off determines how hot the things around it will get once the coolant flow stops.  So the thermostat used will affect the heat soak/hot start issue, since it allows more heat energy to reside in the engine while the engine is running.  If the engine is hotter when it's shut off, the things attached to it will be hotter after it sits for a bit.

[Tony D]

I tend to support my argument with technical background for the benefit of others reading. If people choose to think this means I talk or address people like they don't know what they are talking about, it is in their interpretation. Then again, statements  of irrelevance belying what is stated tend to convey an image that people can judge for themselves. If you want to say it's  an 'attack style' if you can't bring about a cogent counterpoint (you say looking for something new...this is thermodynamics, pretty basic stuff what "New Light" are we to expect?) perhaps consider the argument valid? I don't know, inferred intent is just that, and ad hominem is always a favorite to throw in on both sides. Someone CAN choose to observe these changes, or not. That's not 'ad hominem' that's simply a FACT. I see it daily in distribution training where guys working 20 years on the same equipment have VASTLY different comprehensions of what is going on internally, despite relatively close IQ's (they can test these things overseas, it's not illegal)... My teaching style has always been to call out to students attention things that they MAY not have observed. I've yet to have a class where someone has observed everything I have over the years, and in many cases the guys at the top of their respective companies all see the same things I do. Yes, they show me things they observe, and then we work together on them to understand what is happening. It does exist that people don't WANT to observe. They just take it topically, and go along happily with their assumptions. When they want to argue with someone who has studied things  in depth...it usually isn't pretty.

 

For YEARS I have heard people say the SAME THING you did: The 160 F thermostat runs the engine 'too cool' or 'overcools' the engine.(you still refer to it as "Giving up temperature control"???) I have explained with both the actual unit conversions, and the main issue (from my viewpoint) on why this myth existed: The Thermostat Specification is to open at X and be fully open at X+10 degrees (DEGREES C, not Degrees F!!!). USING THE WRONG UNITS and applying the stated specification comes to the WRONG CONCLUSION. This is somewhat complicated  for some people and it's my intent through thorough explanation and conversion to show WHY this is wrong and change that flawed reasoning. Anybody who reads it and comes away with the basic tenent that Nissan designed around Degrees C and NOT Degrees F will have made a big jump in understanding why a 160F (72C) thermostat is NOT 'overcooling' or 'runs it too cold'. The internet experts flaunt this line and flog it to death, and it's wrong. Remember, you said 'run the engine too cool' or something to that effect. That satement regarding a 72C thermostat is incorrect. Period. And I laid out why.

 

It IS wrong. It DOES convey the impression you do NOT know what you are talking about in this regard. And it is my intent through the explanation to point out this error, and why it is wrong.

 

If you choose to disregard this, and continue to make the same statement, you reveal more. Finally it looks like you came around. That is my sole intent. If you didn't change, then you would be revealing things which would be 'bad' in terms of learning. Such does not seem to be the case.

 

Your last comment does finally convey the point I have been making about the original design of the engine. I stated  this earlier. As well as that the engine should not be having this problem at 91F, nor should yours during the winter on the two occasions when you didn't use the fan. From the start I've said look into it more. The guy weighing in from Texas doesn't get it. You do. In the end you concede the basic points I have made remain uncontested, and are in fact truthful commentary and suitable for others to consider before going forward. That is my intent. Unlike coming on spouting swarf like "Changing the thermostat won't fix the vapor locking (sic) issue, as it happens when the engine is not running, therefor (sic) no coolant is flowing." I have only a limited time to devote to basic automotive education (the difference between "Vapor Lock" and "Heat Soak"), he will have to search a bit more and get his terminology correct to know what he refers to and move forward from there. Ad Hominem? May well be, but it's an ignorant comment to make with absolutely no effort to assist anybody with understanding what is actually happening to cause the phenomenon. Your rebuttal to his remark is correct. It changes the starting point. If he can't see that, and discounts it entirely, what can I do? What can anybody do with someone unwilling to learn?

 

Our man in ABQ is onto it, and the statements from him only require small tweaks but the basics are there and I believe he will be fruitful in his quest... as he retains the flexibility to understand what is being discussed and not ham-hand a solution. The tweaks? Modern cars take into account fuel temperature, not just air and water as on ours. THAT is a BIG difference from the systems in place on these cars. The BTU content of the fuel changes CONSIDERABLY and this is a key to proper AFR. You will find consistent mileage tank-to-tank on CNG Vehicles as their pumps are temperature compensated for BTU content. But on most modern cars you will find consistent MPG, but Inconsistent Miles between Fillups because while the modern vehicle monitors Fuel Temp for BTU compensation and proper AFR, the pumps we use DO NOT. So pumping "hot gas" these days is identical to pumping 'hot gas' back in 1960. There is a resistance to temperature compensated liquid fuel pumps as it takes away a marginal profit margin in a thin margin business already. As to Optimum Temperature, it goes back to thermodynamics and basically the hotter you can run the engine the more 'efficient' it will be adibiatically. This, of course is limited by practical issues of oil selection, and insulation of the components from each other to prevent or promote energy recovery. One thing Caterpillar recently introduced on their big engines is a secondary turbine downstream of the turbocharger outlet which is coupled to a pinion gear and the flywheel through a fluid coupling (think torque converter)---it adds 3% of total horsepower of the engine from waste heat recovery on the turbine! That is significant, and a reason why a diesel is now closer to 50% efficient in terms of BTU input translated to useable torque as compared to Gasoline Engines which are far less efficient. 

 

In the end, racers have known for YEARS the key to keeping the engine making power is to run it HOT. You must run a surfectant to get best transfer of heat, and at least a 24psi cap to combat nucleate boiling. There are PAGES of this discussion in the FAQ stickies at the top of the forums. There are some teams which have run higher pressure caps for one reason or another, to some positive effect, but I can not comment on them for various reasons.

 

As for the PS cooler, I donated a cooler from a 1977 Nissan Cedric, though I see tasty examples on late model Hondas which are usually packaged low and bolted to a front frame member very similar in dimensioning to our frame and cross members. The efficacy of the cooling depends on the thermal layer you can get the cooler into compared to the fuel temperature out of the engine bay. Immersion temperature sensors are preferred, but J or K Thermocouples with hose clamps securing them to the polished fuel piping and then wrapped with some self-fusing silicone tape to prevent air currents from affecting it's pickup of an accurate surface temperature work well, and at Omega.com you can pick them up with long leads, and CHEAP digital displays and rotary switches to flip between multiple thermocouples and utilize a single display. It helps also to have an enthusiastic 8 year old who wants to flip a switch and write down spaceship log readings on a long trip to get it done while driving with the least chance of impacting oncoming traffic! Fuel incoming 'ideal' is somewhat paradoxical as it should simply be 'the same'---that is the ideal! If it doesn't vary, then no adjustments are needed. If you want performance, generally ice cold fuel for maximum but throughput into the engine is used. But you can go the other direction with superheated fuels that are 'vapor phase' to get strange mileage accomplishments in lean-burn setups. Again, each is a 'system' with all components engineered to work together to that common goal.

 

Remember that later S130 ECU's (and I believe the S30 ECUS) used an external 'altitude switch' which leaned out the mix 7% when the contacts were either opened or closed. It was an aneroid bellows and once you hit a given altitude, it changed state and the input to the ECU changed the fueling output. There is your 'altitude density correction'... the MAF cars of course monitored PPH going into the engine, and PPH is PPH regardless of where you are! I have used that switch input in testing some times to tell what happens if I lean out 7%...

[Tony D]

What the long and short of what the above says is "I'm nailing down the KNOWN VARIABLES."

 

When someone says, 'it should not happen'---the way forward is to VERIFY the 'known variables' are within the acceptable data set, and IF SO, then begin the search elsewhere.

 

NOWHERE did I dispute fuel as a causatory factor. On several occasions I stated this. How it was missed I can't say, I thought I pretty much stated that very early in the conversation...

 

But what I see time and time again is people SKIP verification of the 'known variables' and go down a wild goose chase due to starting with poorly supported initial assumptions.

 

I thought I left quite a bit leeway in deciding how to repair it, I just tried to make clear the internet myth on the 160 (72C) thermostat was sorely mistaken...outright WRONG.

 

It was an attempt to keep people looking towards OEM solutions rather than reengineering components that were VERY well thought out indeed. 

 

Much like HybridZ's Aerodynamic Testing, JeffP's Oil Temperature Testing revealed quite a bit about what is going on inside the engine. And what myths existed in regards to 'runaway' cooling issues. This is all covered more or less, in the L-Series Cooling Sticky in the FAQ.

[NewZed]

I wrote up a whole thing here but realized I was just churning up dust.

 

We're still left with two potential fixes for the hot start problem.  A cooler than recommended thermostat (deviation from the FSM instructions based on Tony D's advice) or a cooling fan (modified from the factory ZX fan scheme, to blow air directly on to the injectors).  Both deviations from factory, and apparently both work.  A choice.

 

The reasons that Nissan used three different thermostats are still unclear, as many things are since we don't have the notes or minutes from the decision-making meetings.  But Tony D has listed many of the effects of using coolant temperature control.  Removal of the heat soak being one potential benefit.

 

I still disagree that using the fan to solve the problem, while keeping the hotter thermostat is incorrect, in any way.  It's just another way to get a job done, completely within the parameters of correct and careful engine operation and maintenance. 

 

Using the 160 thermostat is just the Tony D way, and incorrect, by the instructions of the Nissan engineers.  It's just the way it is.  There's nothing wrong with deviating from instructions, but you do lose the right to say other people are doing it "wrong".  Better to say "here's how I do it and here's why I think it's a better way".   Somewhere in the last page or two I think there is some of that along with a lot of extra stuff.  Even better, in addition, explain what the Nissan engineers were thinking, if you know, for context.

 

I'll still be searching around for information on the effects of combustion chamber temperature on performance and how that can be affected by coolant temperature, in addition to effects on lubrication and clearances.  Ideally, one could summarize things down to pros and cons of hot versus cold, for use in decision-making.  Maybe it's all hidden in this thread somewhere.

[Tony D]

"We're still left with two potential fixes for the hot start problem.  A cooler than recommended thermostat (deviation from the FSM instructions based on Tony D's advice) or a cooling fan (modified from the factory ZX fan scheme, to blow air directly on to the injectors).  Both deviations from factory, and apparently both work.  A choice."

 

This indicates a structural impasse due to lack of comprehension and obsession with disregarding sound logical approach. Words mean things and you simply can not grasp the fact that 160F thermostat is NOT 'cooler than recommended' on a 90F day! It doesn't OPERATE at 160F. There ARE proper, logical steps to problem solving. Skip steps, you end up with problems. I make a good living going back to the BASICS daily, and correcting shadetree bandaid fixes by people who used anecdotes or poor observation to solve THEIR problem, and then applied it to someone else's issue which LOOKED similar. I merely lay out the parameters and logic for someone else. You wanna disagree, go ahead. You haven't offered ANYTHING other than 'it worked in my case" (anecdotal.) Moreover, you haven't done anything but (like a pair of croaking frogs) said "it won't work, didn't work for me"---who is to say it isn't EXACTLY as I have offered and a fuel issue in your case? No supporting evidence, no checks, no showing of the work or troubleshooting leading up to the conclusion of WHY it works "in your case".... More important, no refutation that SUNLIGHT causes Hot Start issues as it only happened on MY car during the day time, never at night.... This is the line of thinking you bring to the conversation. Please, a little more thought, less supposition!

 

"Even better, in addition, explain what the Nissan engineers were thinking, if you know, for context."

I've done that, repeatedly, but as stated in the previous paragraph you choose to malign my intent and my discussions with them on this subject (as well as others in the aftermarket...)

 

I ALSO proffered the following: LEAKING FUEL PUMP CHECK VALVE (especially for someone who has hot-start issues in winter when an injector cooling fan was left not running...) and have mentioned several other avenues of approach.

 

It is obviously now a fishing expedition for a reaction for some reason. And I'm done with this dead-end conversation. When you get someone who simply can't understand what you're telling them (or worse, chooses to disagree just to make a scene and add nothing other than contradiction), and then consciously chooses inflammatory words and misstatement of prior topics covered exhaustively, you only have to question what their pathetic motivations are. Sad, truly sad.

 

I head to the control panel now...

[NewZed]

This indicates a structural impasse due to lack of comprehension and obsession with disregarding sound logical approach. ....

 

and then consciously chooses inflammatory words and misstatement of prior topics covered exhaustively, you only have to question what their pathetic motivations are.

 

Sad, truly sad.

 

And I'm done with this dead-end conversation.

I've taken a few items for general response.  The last two out of order.

 

These first two things are just odd, and disingenuous, and might be self-reflective.  None of it applies to me, I've never been accused of anything similar by anyone, ever, and I've never felt an inkling that I should examine what I was doing because some of these things might apply.

 

It is sad.  If there was anyone out there that I thought could dig in to this issue and come up with some rational reasons for why it happens and how to stop it, it would be you (and several others who have may have seen this thread but knew better than to get involved).  Maybe though, this is your "white whale" and you're having trouble dealing with the fact that it can't be caught.  You don't understand it so you just keep throwing the same old harpoon.  Or you could just be a bully, in general, and can't stand to lose a bullying session.  That actually fits with some of the other threads you've been a part of.

 

Now you've given up and taken the path of full-on verbal personal abuse and bluster, in public.  That is truly sad.  As you're trolling the internet in the future looking for some newbie to abuse, or a thread to interject your FACTS! in to, put a little more thought in to where it could lead.  Think about leaving sooner.  This is a pretty ugly end to what was an informative thread.

 

You can do better Tony D.  Still lots of time left.

[Nigel]

I've been battling hot start issues from pretty much day one after my L28 Turbo conversion in my 240Z. I can get it to fire up, but it dies almost immediately. I'm running SDS EFI fuel injection, with a '75 intake manifold, RX-7 Injectors with a custom barbed fuel rail that's isolated from the manifold. I'm running the 82C thermostat. I have zero issues with over heating. The coolant runs in the 180's on the highway. The car ran at the track in Nashville in mid 90F temps, and I've sat idling for over an hour in 90F heat at a border crossing. The coolant will get up into the 190's in those conditions but that because that's where I have my electric fan set to operate (SPAL PWM variable speed controller). The SDS system includes a fuel prime, but it doesn't help. Even repeatedly cycling it makes no real significant difference. Fuel pressure holds after the prime. Over the years, I've tried a number of things (just about everything mentioned in this thread) to address the hot start issue, but none have solved it. They include:

• Moving the air temp sensor from the intake manifold to the outlet end tank of the intercooler.
• Multi-layer reflective heat shield under the intake manifold.
• Insulating blanket over the exhaust manifold.
• SS Turbine heat shield.
• Exhaust wrap on the down pipe.
• Reflective sheilding wrap on fuel lines in the transmission tunnel
• Reflective sheilding wrap on the fuel rail
• Fuel cooler after the fuel pump
• Competition hood vent

I've researched hot start issues on this forum and others for years and years, but I've never been able to find a conclusive common denominator for why some people have hot start issues and others don't. This is the first time I've heard of using a cooler thermostat in the context of combating hot start issues. There's no evidence that I can find that Nissan intended the tropical thermostat to be used to combat hot start issues. I can't even find any definition in the factory service manual as to what conditions each of thermostats available should be used under. If solving hot start issues was as simple as using a colder thermostat, then why did they waste time and money developing and installing injector cooling fans? If it's due to emissions requirements, then how could they offer a tropical thermostat in the first place? Based on the era these cars were made, I think the purpose of a tropical thermostat had to do with the limitations of the oil and coolant of the day more than anything else. 

 

Regardless, using that approach to keep the injectors cooler may very well work. But this seems like just as much a band aid solution as anything else, since it's not without negative consequence. I'm not a fan of reducing efficiency by sending more energy into the cooling system rather than making the car move forward. I'm also reluctant to start messing with a system in my car that in functions perfectly well in every other way.

 

The only thing that I've found that helps my hot start issue is by manually running the radiator fan after shut-down for a few minutes. So, I have a couple of ideas in mind that I may try. I may lower the set point the electric fan kicks in. But I don't want to go so low that it's running while cruising around. It starts out at 50% at around 190F. And this would only help if I let the car idle for a while before turning it off. I do have an injector cooling fan that I may install. I found a handy inexpensive timer module (Velleman VM188) that I was going to use in combination with a temperature switch to control it. But a simpler solution may be to use the timer to keep the SPAL fan controller powered for X minutes after the ignition is shut off so it can continue to run the fan as needed. I think this is what I'm going to try first. Since the SPAL controller only runs the fan as hard as is needed, it shouldn't put too much of a strain on the battery. I'll be hooking this up this weekend.

 

Nigel

[NewZed]

For anyone interested, here's the Grape Ape Technical Articles site.  The Cooling link has good descriptions of the basics.

 

http://mysite.verizon.net/vzezeqah/id1.html

 

Odd that it doesn't have Grape Ape in the link, but I think someone moved the files over.  It seems to be the real deal.

 

 

Nigel, on the use of a fan, mine is a ZX fuel system cooling fan (described in 1981 FSM EF-46) with a GM heat riser tube attached to the fan's outlet and laid down under the fuel rail on the L6.  The end of the tube is plugged and 6 holes, ~1/2 diameter are used to direct air directly on to each injector.  The rest of the engine just stews in its own heat, no fan, no hood vents.  Only the injectors get air, drawn from the right above the oil filter.  The fan is run off of a bathroom fan timer, mounted by the steering column, the factory thermal switch is not used.  Your problem is really interesting since your engine is quite a bit different from a typical NA L6. 

 

Here's a link to the type of heat riser tube, it's the typical accordion-fold metal/fabric material hose that GM used to bring warm air up to the intake manifold.  I got mine from wrecking yard S10's.

 

http://www.amazon.com/Standard-Motor-Products-Pre-Heater-Hose/dp/B000C7UPQU/ref=wl_it_dp_o_pd_S_nC?ie=UTF8&colid=30R38L6H5WA0Q&coliid=I2PEPLP3OQMVN8

 

Coincidentally, I forgot to turn the fan on twice today (subconscious maybe...) and got typical heat soak/hot start problems.  As it clears up it seems like one injector takes longer to clear up than others.  Runs on 5 cylinders for a while.  The second time the temperature gauge was still reading normal.  Who knows, a 160 thermostat might help.  I'm running Bosch 028150116 injectors, not the stock Nissan green ones.  Just filling out the picture.

Edited July 19, 2013 by NewZed

[Tony D]

Short form Nigel,

The Tropical wasn't engineered for hot start issues per-se. It was a system change to address ambient issues to the entire system. The coolant hasn't changed since they were designed. Same EG 50/50 or whatever...  

 

The Emissions issue is moot, regarding the tropical thermostat. I swear, guys, for the last and final time, OPERATING TEMPERATURE OF THE TROPICAL THERMOSTAT SATISFIES ALL SENSORS ON THE VEHICLE IN REGARD TO ENABLING EGR/CLOSED LOOP ON ZX'S/THERMAL VACUUM SWITCHING.... Nowhere has it been said that a functioning vehicle needs to change anything. But if you aren't functioning....and haven't changed it....consider it. The changing of the thermostat is to prevent runaway overheating due to nucleate boiling which IS a known problem in these vehicles. Asked another way: Why is it in the parts catalog if it's not necessary? Why offer three different ranges and designate them? Why? This is EXACTLY what I referred to in KTM's case. No matter what, in SoCal he was experiencing runaway overheating. No hot start issues, but come off a highway and go to an onramp sitting at idle and BOOM! Put in the 160...it goes away. YES, you could put a 24psi cap on there and accomplish the same thing... But at what cost (heater core leaks, radiator leaks, etc.... never know.... lower the temp or boost the pressure cooker's pressure. Lets not address Boston using this analogy.)

 

As for your location and your temperatures, please review my studies on East Coast / West Coast. The aerosols in the atmosphere east of the Rockies (more as you head east) contains progressively more aerosols filtering UV to a greater extent. The thermal layers the radiator passes through on a 90F Toronto Day trucking up the QEW (from my trip through on the way to the Zedaway, 2001) were around 98-103F. Compare this to the 85F day in Baker CA with a 120-130F Thermal Layer. The exchange you get through the radiator from the cooling flow is less. I forget the approach temperature of the radiator...10/20F over cooling medium, you see that on a 90F Toronto day, with a set rise across the engine (or set outlet temperature of XXX) you get interesting results. With a 100F thermal layer, the best you can expect out of the radiator is 110/120 with the given approach. With the median of 125F thermal layer at 85F (less) ambient in CA, the best you will get out of that same radiator is 135/145.... if you have BTU input to get a 30 F rise across the engine, you are fine in Toronto at 90 (120+30=150, plenty of margin), but getting much closer to thermal issues (145+30=175). This assumes stasis, and at that temperature one would have a thermostat closing quite a bit (a 160 180 190 thermostat would not be open at those conditions in Toronto) but in CA you have a 160 thermostat well open and flowing, the 180 or 190s wouldnt be open. Get it a bit hotter and you can see where people got runaway overheating in the desert southwest. 

 

When the engine bay temp starts rising, it affects other things. Fuel in rails can boil (low pressure vapor lock in the 240's and 260's.) Heat soak in later vehicles.

 

"The only thing that I've found that helps my hot start issue is by manually running the radiator fan after shut-down for a few minutes. "

 

Pushing the heat out of the engine bay accumulated there -- others accomplish this by cutting two 3" holes to vent the engine bay to the inner fenders under the battery and the Master Vac. Putting those holes near the firewall to low pressure area evacuates a HUGE air-dam created at speed, and DRAMATICALLY reduces underhood temperatures. As much as you reduce the underhood temperatures from going from 82 to 72 and then some more! And its great if your racing class allows it (mine does not.) Some people would say put some pancake fans on those holes and have them activate above XXX Degrees and issues go away. These cars heat dam under the hood. The 'competition hood vent' was a vapor lock solution because of excess underhood temperatures. Cutting a hole in the hood was a last ditch way to get the heat out. Prior to that... well, read the Flat Top Service Brochures you will see there were several other steps to take before resorting to the hood vent. It's posted online, I'm pretty sure. I'll let you find those "prior steps".

 

Until this time, we were discussing stock vehicles and stock vehicle dynamics (with the reference to KTM hitting that runaway situation since it was posted here and very well documented as opposed to anecdotal comments. A guy with instruments without a solution who tried all the fancy stuff and couldn't get the answer. Tried the basics, and it went away.) If you get into modified engines, then there are myriad of control variables introduced. I know JeffP's car has no hot start issues, nor overheating now, even when making 470HP 5 minute dyno pulls. But that engine is not stock in induction, nor cooling system...it's listed in the cooling sticky.

Edited July 19, 2013 by Tony D

[Pharaohabq]

Well here's an idea I was just thinking of when reading about cutting holes in the fenderwells.  Would a good test of this be to drive around a bit with your hood popped open just locked on the safety latch?  In doing so would allow excess heat to escape and you wouldn't necessarilly  build as much ambient heat in the compartment.  If that made your stalling issue go away, then we'd definitely know it's a heat based issue and could try using a lower temp thermostat.  On the 260Z we're putting in the tropical thermo, but had to have autozone order it since they didn't have it in stock.  I'll let you know what kind of difference it makes once we get it installed and get to run a while.  

 

Now I know the windshield is a HP area, but I'm hoping enough air would be pushed out to make the difference under the hood.

 

If that sounds like a good test, it would certainly be worth trying before making additional mods on the engine, adding fans/changing thermostats/swapping in chipmunks.

[Tony D]

I do that regularly, there is a measurable difference, but in that instance you are venting to high pressure, not as effective as a smaller hole to lower pressure (Like the stock ZXT BOV in #4 Runner).

 

If you can find the 1/4 mile comparo Norm S. did on leaving his hood OFF the latch while drag racing. It's more of an effect of air pressure relief in that instance and it's disconcerting to have the hood halfway open at the big end of the pass doing 12 second passes! But it worked.  I would say the holes into the firewall are more efficient in venting than merely cracking the hood (though I do run cracked in the summer.)

[Pharaohabq]

NewZed, Could you try running with your hood popped on the safety latch a couple days, without using your extra fan and let us know if you experience any heatsoak/vapor locking issues?  I'd really like to know if this is a valid test.  It's only a test,  I want to know if it lowers the ambient underhood temperatures, and also if that in turn affects heat soak from the block.  If removing heat from the compartment makes a big difference then we know there's something of a design issue. (of course, we know there is since Datsun put in the hood vents, and later the injector fans).

 

I suppose some kevlar or ceramic insulators under the fuel rail mounts may also help, unless almost all of the soak is through the air, rather than metal to metal contact... 

 

It would be fun to put thermocouples on the intake and return fuel hoses to see exactly how much heat is transfered to the fuel at running temp.

[NewZed]

Sounds interesting but you've basically moved on to basic engine parts cooling.  My main interest was in the pros and cons of the 72 degree thermostat versus the 82 degree.  Basically, is there a trade-off in running one thermostat versus another.  I have a fix for injector heat soak, I'm just trying to learn more other stuff, in general.

 

Sorry I can't help but it bothers me just to see pictures of Z's with the hood cracked, let alone drive around that way (no offense to those who do).  Plus putting up with all of the people trying to signal me that my hood is open as I drive around.

[Nigel]

The Emissions issue is moot, regarding the tropical thermostat. I swear, guys, for the last and final time, OPERATING TEMPERATURE OF THE TROPICAL THERMOSTAT SATISFIES ALL SENSORS ON THE VEHICLE IN REGARD TO ENABLING EGR/CLOSED LOOP ON ZX'S/THERMAL VACUUM SWITCHING....

I never said it didn't.

 

Asked another way: Why is it in the parts catalog if it's not necessary? Why offer three different ranges and designate them? Why? This is EXACTLY what I referred to in KTM's case. No matter what, in SoCal he was experiencing runaway overheating. No hot start issues, but come off a highway and go to an onramp sitting at idle and BOOM! Put in the 160...it goes away. YES, you could put a 24psi cap on there and accomplish the same thing... But at what cost (heater core leaks, radiator leaks, etc.... never know.... lower the temp or boost the pressure cooker's pressure. Lets not address Boston using this analogy.

I never said other thermostats weren't necessary. But we're talking about 30+ year old cars with poor quality oils, inconsistent block and head castings, less efficient radiators, and questionable aerodynamics. So, Nissan offered a few different thermostats to hedge their bets.

 

 

 

NewZed, Could you try running with your hood popped on the safety latch a couple days, without using your extra fan and let us know if you experience any heatsoak/vapor locking issues?  I'd really like to know if this is a valid test.  It's only a test,  I want to know if it lowers the ambient underhood temperatures, and also if that in turn affects heat soak from the block.  If removing heat from the compartment makes a big difference then we know there's something of a design issue. (of course, we know there is since Datsun put in the hood vents, and later the injector fans).

 

I suppose some kevlar or ceramic insulators under the fuel rail mounts may also help, unless almost all of the soak is through the air, rather than metal to metal contact... 

 

It would be fun to put thermocouples on the intake and return fuel hoses to see exactly how much heat is transfered to the fuel at running temp.

I have the competition hood vent and I cut the biggest hole in the hood that I could. It's the length of the block and the width of the hood bulge. I didn't see much of an improvement in hot starts. With out some sort of fan to force the hot air out, it still gets trapped in the engine bay when the car is stationary.

 

I don't believe a hot fuel rail is the real issue. My fuel rail is isolated by rubber, and it only feels warm when I have hot start issues. I believe the issue is with the heat of the injectors themselves. They're right next to the head, and only inches away from the exhaust manifold. I've touched them, and they get scorching hot. This is the inherent problem with a non-cross flow head. I've found that even repeated priming of the rail isn't enough to flush out the hot fuel from the injectors. It only clears out the rail. I've wondered if getting rid of the injector retainers would help, if they're acting like an insulator to keep the heat in.

 

Nigel

Edited July 23, 2013 by Nigel

[NewZed]

I've wondered if getting rid of the injector retainers would help, if they're acting like an insulator to keep the heat in.

 

Nigel

I've wondered about the insulators (retainers) also.  I have the open type on my engine now, the kind with the stand-offs that leave the injector body exposed (might be why the fan works for me).  It sounds like you might have the enclosed type that look like they would retain heat.  One exposes the injector body to radiant heat, the other shields the body from convective cooling.  Which is worse?

 

On the manifolds - I wonder if people with headers have less problem since the mass of the header pipes is less than the mass of the factory cast manifold.

 

 

I am pretty sure it was cgsheen that suggested side-feed injectors would help avoid the problem since they run fuel around or through the body instead of passing it over a supply hose.  With our injectors the fuel passes ~2 inches away from the injector body, only convection mixes cool fuel with hot during a prime.

[RebekahsZ]

Before you do anything else, have a shot of vodka. That's what the Russians use in their radiators, then if your car breaks down you can have a party and all your friends will come over to help.

[Tony D]

"It would be fun to put thermocouples on the intake and return fuel hoses to see exactly how much heat is transfered to the fuel at running temp."

 

Been done, dismissed here as anecdotal, so no need to dig up the numbers again. They were both "on" and "in" during that testing, as well as in the tank.