Coolant Circulation Bypass Line

[Tony D]

This post is of interest to me because my car does not have one and I didn't think the engine had been modified before I got to messing with it.... '83 turbo...

Sure enough does---comes from under the thermostat, thorught the heater block in the throttle body, the heater block under the Cold Start Ari Vavle (whatever it's acronym is) then returns via a 10mm line around the front of the engine to the inlet of the water pump through the fitting that is vertical in the inlet to the pump.

[Tony D]

My two cents worth.

 

In my opinion' date=' the external cooling line from the waterpump inlet (bottom radiator hose) to the back of the engine over to the carbs through the carb thermostat through both carbs and back to the underside of the thermostat housing is NOT a coolant return line for block circulation when the engine thermostat is closed. The purpose of the line is to heat the carbs to more effeiciently atomize the fuel to reduce unburned fuel out the exhaust pipe therefore reduceing tailpipe hydrocarbons. Something the EPA was very woried about in the 70's.[/quote']

 

It is a bypass line, and in the later 73/74 cars, the circuit was modified to two circuits (one which had a thermostat that closed by 170 degrees...curiously the temperature at which the EGR became enabled...) But the other 10mm line remained flowing, thought through an 8mm orifice. The problem was that the cars had a vapor lock problem in those years, and restricting the recirculation on the line helps alleviate this. BTW, the "reverse thermostat" you mention goes to prove the point that the recirculation line is deemed crucial by Nissan, and after the thermostat is opened (the tropical thermostat Nissan has is fully open by 170 degrees, btw!) the line is not necessary.

 

All the cars had a bypass line, and when the SU's were removed, the line was changed to another routing. There is a big consideration for the EPA, to be sure, but even on the JDM engines, there is a 10mm line that goes from the thermostat lower housing, around the front of the block, to the pump inlet---going through nothing on the manifold---this is the way it is on my 78 Fairlady 280Z(X) while the 83 has the routing shown above. The difference between JDM, NON-US, and US Specific Models.

 

It's more of an anti-icing issue, really, and aids in cold start running, the JDM cars had the same circuit, because the SU's don't do a good job when cold. The circuit helps with getting the car off the starter circuit earlier.

 

Which in turn reduces the....

[Tony D]

Tony, I’m not trying to be rude here, but you did jump into this thread sort of “screaming” and posting with a demeaning attitude.

 

I don't think I did that in the least bit. I emphasise certian words, perhaps I should edit it to use italics, but caps on a word actually conveys the way I speak. Anyone who has talked with me, and heard me speak will know that I will emphasise words with a raised tone. Not yelling, but there's no "half caps" unless I type a bunch of HTML in there. Not that I wish the emphasise Hyp...er, 'html in caps'...

 

Oh, wait, this is being P.C. now....

 

Would everyone feel better if I went back and edited my post to italics or bold italics instead of the caps for the individual words? I'm not typing in allcaps, only certian words.

 

And to the point in the post, many of the things you mentioned were mandated by the USEPA (er, acronyms are O.K. to capatalize, right? and O.K. is O.K. to capatalize as well, right?) and Nissan would have loved to run along without them. Matter of fact, in most markets outside the USA (er, USA is O.K. to capatalize, right?) these terrible abominations did not exist on the S30 series.

 

But one thing remained constant: the bypass line from the lower thermostat housing, to the pump inlet to compliment the internal bypass line on the oil filter side of the engine. It was available, and present in every market.

 

Please don't confuse a component designed by the manufacturer, and one dictated or mandated by a govermental agency! Remember the Honda CVCC was required to run a catalyst in 1981, even though the engine, due to superior engineering and design, met all required emissions criteria set forth by the USEPA. The EPA mandated EGR, they did not leave it up to the automakers to come up with their own, unique pollution remedies.

 

So please, remember things on an engine may be there from the manufacturer, or from the government.

 

The Thermostatic Bypass Line is not one of them. It's on SBC's from the 50's...

 

Now, as to this:

"On modern throttle valves, early ‘80’s and up, Nissan also added a coolant port to the throttle valves thus pumping 185+ degree coolant through and around the throttle valve. In fact, most, if not all auto makers are also doing this. (We tuners prefer to NOT preheat the incoming air charge)."

While you may not like to preheat the charge, the automakers do, due to the litigiousness inherent in the system these days. Throttle Icing---serious throttle icing, is nothing to sneeze at! Having gone through an almost tragic incident involving my throttle plates being blocked 1/4 open due to throttle icing, I tend to run a bit of preheat... This was more of an issue on carburettors, but it can happen at low throttle openings on EFI cars as well. Would I recomend removing the preheat line? Probably... I would also inform the owner why I was doing it, what he could expect in performance gains (er...minimal) and the oft chance that his throttle might stick partially open in some combinations of ambient temperature, humidity, and manifold vacuum situations. Does this have anything to do with water pump cavitation and the bypass line? No. But it does illustrate a point: Know why it's there in the first place before you go disconnecting things willy-nilly because someone on the internet said it was O.K.! Many people have grave misinformation about why some components are on the vehicle in the first place, and they are the dangerous parrots who squawk myths and legends and turn kids round the wrong way when advising them on this great internet medium.

 

Once people know why a component is installed, and what it's function is, then maybe they can make an informed choice about it's removal. But to just cap it, or yank it out....well whatever floats yer boat I guess!

[Tony D]

I mistrust anyone who arrogantly insists they are right and everyone else is wrong all of the time... that is a sure sign they have issues with truth and facts.

 

That's uncalled for bj, and is simply an extension of your ranting elsewhere. I never said everyone else is wrong, nor have I said I am right all the time.

 

Though, you seem to have issues with reading comprehension regarding the other matter. I live in a world where more than one person can be right. But then again I'm not insisting anything. There can be two sets of facts that each are correct. If you fail to see that, or comprehend that, then I feel sorry for you.

 

Hell, I even found Zane's "Lion Rock" comment hilarious! I'm going to use it myself. Probably in response to a post by you in the near future. Lighten up, dude, quit taking yourself so seriously. I do.

[Tony D]

Just an aside, now that we've separated governmental mandates, and equipment that the Z was actually designed to have---I mean, am I totally off base in the arguement? If Nissan could save the money by leaving it off, ask youself the honest question: "wouldn't they?" I mean, EVERY engine designed for passenger car usage has a bypass line to prevent cavitation of the pump and it's pump cavity during times when the thermostat is closed, and the flow from the centrifugal pump is restricted below the flow curve for the impeller used.

That is the real reason for the bypass line---the "piggyback" usages of it for manifold heating, etc etc etc are one of those things that engineers do when they say "well, we have this line here that can be rerouted"...

 

I mean, if you plug off the second bypass, does the internal bypass flow enough water for the pump not to cavitate? You are effectively halving the flow through the pump during the warmup period.

 

This post has gone a long way towards revealing a lot of people's understanding of the workings of the Internal Combustion Engine, that's for sure. Some people even mentioned damaged housings relating to overheating---ever notice a "pockmarked" front cover in the water pump impeller area? An area so erroded it looks like at some time terrible corrosion had occurred, yet there is nothign there when you pull it apart but pockmarks in the diecast?

 

Care to venture a guess what the evidence of pump cavitation looks like?

 

I'm sure it's not the same circular gouging that occurs when an impeller thrashes the casing----but then again you wouldn't notice it if that's what you thought caused it, would you? Or you would simply thinkn "corrosion"...

 

Never "Pump Cavitation During Warmup"---when you know what cavitation looks like, you can identify it. And when you know cavitation is caused by a number of things, including too high incoming fluid temperature, insufficient flow, low NPSH....well you can see how these things can feed off one another. If you halve the flow coming in before the engine is up to temperature, you can get low NPSH while at the same time having an inlet temperature (that, while at a higher flowrate for the impeller would not cause a problem) that is high enough to cavitate the pump.

 

Curious, slowing the pump down helped prevent overheating...

Could that have been because slowing down the pump speed dropped the flow rates back within the design pump curve, and allowed the pump to operate without cavitating (which causes a flow loss, as well...)

 

I may know what I'm talking about after all. Though feel free to disagree, and do as you will. It makes no whit one way nor t'other to me. I just find it funny to read this stuff sometimes. I really do.

[briann510]

Oh man... 5 in a row Tony!

[Tony D]

Yeah, I go down and read em, and reply.

Each comment has a specific reply, wouldn't want to group them all together, and insult anyone or cause the possibility of cross-talking between who said what when...

Besides, what else do I have to do? It's freakin' LIVERPOOL (and that is shouting!) for gawds' sake! Rainy, dreary, cold....

Eh, it's 9pm now, guess it's time for a couple of Pints 'o Guinness, and the rack...

 

On the upside, I got to take a ride home today in a Lotus Elise! :^)

[BRAAP]

….

Would everyone feel better if I went back and edited my post to italics or bold italics instead of the caps for the individual words? I'm not typing in all caps' date=' only certain words……

 

…..Now, as to this:

"On modern throttle valves, early ‘80’s and up, Nissan also added a coolant port to the throttle valves thus pumping 185+ degree coolant through and around the throttle valve. In fact, most, if not all auto makers are also doing this. (We tuners prefer to NOT preheat the incoming air charge)."

While you may not like to preheat the charge, the automakers do, due to the litigiousness inherent in the system these days. Throttle Icing---serious throttle icing, is nothing to sneeze at! Having gone through an almost tragic incident involving my throttle plates being blocked 1/4 open due to throttle icing, I tend to run a bit of preheat... This was more of an issue on carburetors, but it can happen at low throttle openings on EFI cars as well. Would I recommend removing the preheat line? Probably... I would also inform the owner why I was doing it, what he could expect in performance gains (er...minimal) and the oft chance that his throttle might stick partially open in some combinations of ambient temperature, humidity, and manifold vacuum situations. Does this have anything to do with water pump cavitation and the bypass line? No. But it does illustrate a point: Know [b']why[/b] it's there in the first place before you go disconnecting things willy-nilly because someone on the internet said it was O.K.! Many people have grave misinformation about why some components are on the vehicle in the first place, and they are the dangerous parrots who squawk myths and legends and turn kids round the wrong way when advising them on this great internet medium.

 

Once people know why a component is installed, and what it's function is, then maybe they can make an informed choice about it's removal. But to just cap it, or yank it out....well whatever floats yer boat I guess!......

 

Quoted in another reply…..

 

This post has gone a long way towards revealing a lot of people's understanding of the workings of the Internal Combustion Engine, that's for sure. Some people even mentioned damaged housings relating to overheating---ever notice a "pockmarked" front cover in the water pump impeller area? An area so eroded it looks like at some time terrible corrosion had occurred, yet there is nothing there when you pull it apart but pockmarks in the die cast?

 

Care to venture a guess what the evidence of pump cavitation looks like?

 

I'm sure it's not the same circular gouging that occurs when an impeller thrashes the casing----but then again you wouldn't notice it if that's what you thought caused it, would you? Or you would simply thinkn "corrosion"...

 

 

 

 

 

Tony,

First off, thank you for the informational replies and to me at least, you came across with less attitude.

 

As for the caps and italics for your post, that does help accentuate key aspects within your posts, but I’m not so sure that just adding caps or italics would take the attitude out of your original posts, though all your replies since, (to me any how), have had a much more friendly attitude which is greatly appreciated, thank you.

 

You bring up valid points and seem to be well versed in “how” and “what” the OEM is bound to legally. Curious, what is your educational and practical background in regards to power-plant development, building, and tuning?

 

In regards to the throttle valve pre-heat, in adding to your assessment of the anti-icing capabilities, I also believe it fulfills another function as well and that would be Emissions. By adding a consistent heat to the throttle valve, this helps to “stabilize” inlet air temps, by what little heat it does add to the air stream, thus helping keep tighter reigns on emissions control. As a Certified Aircraft technician, (acquired my A&P certs in ’91), and a private pilot as well, I’m quite aware of the effects of throttle icing and how it forms. On Fuel injected engines throttle icing is “almost” non existent and as such, the “carb heat” control found on all carbureted air craft was eliminated on injected aircraft, that is not say throttle icing doesn’t happen on injected engines, and I do believe when conditions are just right, temps, humidity, throttle position, etc, the temp drop at the butterfly, even without fuel atomizing at the butterflies, can be enough to ice. In a carb application, the heat being removed from the air stream due to the atomization of the fuel exaggerates the temp drop across the butterfly so icing DOES happen and it happens more often then most people realize. I’ve experienced this first hand a couple times while flying around Mt Hood here in the Pacific Northwest on cool humid days. Constant application of Carb heat at regular intervals helps keep the carb clear for optimum performance, i.e. able to remain ABOVE the terrain! As pilots, we are trained that Carb Icing can even happen at ambient temps as high as 70 Degrees F during high humidity etc, though the only times I’ve personally experienced carb ice while flying is when ambient temps were down in the mid to high 30’s at altitude.

 

As for the divots/erosion/corrosion/pock marking found on the front cover behind the impeller, were you eluding to this being caused from cavitation alone? Cavitation, as you stated, is not good on many levels, as coolant flow will, for the most part, become non existent during cavitation, and that a reduction in impeller speed would improve cooling in that situation, which I agree with 100%. I am struggling with the concept that the forces present during cavitation within the Datsun water pump are strong enough to “mine” the aluminum from the front cover itself yet does no damage to the impeller blades, i.e. bent, broken, pockmarked etc. I realize the impellers are made of a harder material, typically mild steel, but most of them are just stamped sheet metal and as such, I would think they would also show some signs of damage as well. At any rate, I “used to be” fairly confident in saying those divots in the front cover under the impeller were caused from Electrolysis as a result of negligent cooling system maintenance, and usually those same engines that had this front cover problem also had the water jacket transfer ports on the deck surface of the cylinder head eaten away as well. Now I am VERY confident in saying the cylinder head coolant port erosion is caused from Electrolysis, but if those pock marks, (little round divots), in the front cover are from cavitation, please help me understand why that is and the physics taking place to cause this? If my original concept of Electrolysis causing those divots is incorrect, I need to know.

 

As you stated, a coolant bypass is a MUST, and how that bypass is implemented is one of those things that not everyone will agree on. When most people eliminate the external water bypass on their engines, they will typically make provisions for a coolant bypass such as drilling the thermostat itself. The coolant bypass is a must for various reasons like Tony stated, such as to help prevent cavitation of the water pump while the thermostat is closed, to help “burp” the cooling system on an initial fill, and to a much greater degree, for the purpose of allowing the heated coolant to flow up to the thermostat itself so that the thermostat can “sense” the heat being generated by the engine and in turn modulate coolant flow accordingly. If no hot water/coolant makes its way to the thermostat, then it is surrounded only with cool water/coolant, i.e. the thermostat has no idea the engine is getting HOT. Being as the thermostat is remotely located in relation to the combustion chambers, i.e. not directly on top of the combustion chambers themselves, “if” there is NO coolant flow whatsoever, the only way the thermostat could sense the heat being generated by the engine is from conduction, which is a slow process. By the time enough heat has been “conducted” up to the thermostat to open it and let cool water to surround the cylinders and combustion chambers, it would be too late. So by allowing the coolant to flow up to, under, and/or thorough, the thermostat itself, the coolant that is being heated by the combustion process gets a chance to cycle up to the thermostat so it can “sense” the heat being produced and fulfill its duties of maintaining a consistent running engine temp. This is a major function of that external coolant bypass that most of us do eliminate, we just need to make sure an alternative bypass has been provided in its place.

[briann510]

I figured you (Tony), was in some 3rd world country with nothing else to do while off work. I mean how many burro shows can a person actually go watch....LOL

[thehelix112]

But one thing remained constant: the bypass line from the lower thermostat housing, to the pump inlet to compliment the internal bypass line on the oil filter side of the engine. It was available, and present in every[/i'] market.

 

From the lower side of the thermostat housing you say? My engine doesn't have one, and neither does my old L24. That being said I'm with zguy36, I am eager to learn about overheating problems as I'm getting really sick of changing head gaskets and am getting ready to start pushing a little over 500hp from mine.

 

One bloke here in Melbourne (Australia) has `drilled the back of the head' to improve the coolant flow stuff. TO be honest I don't fully understand it all. I need pictures.

 

Does the water flow into the engine down the.. err.. spark plug side, past all the cylinders, then around, then back down the manifold side to the thermostat. If thermostat closed then how does it circulate? Through the heater? I have the heater outlet at the rear spark plug side of the head diverting straight back to water pump. :S Stupid coolant.

 

Dave

[Tony D]

"I am struggling with the concept that the forces present during cavitation within the Datsun water pump are strong enough to “mine” the aluminum from the front cover itself yet does no damage to the impeller blades, i.e. bent, broken, pockmarked etc."

 

 

I have seen cylinder liner failures from ductile spuncast iron due to cavitation damage! I could take some photos if I wasn't like 7000 miles from my "example liner" (now a convienient trash can!).

 

Many times the cast iron blades will be cavitated and erroded as well. Errosion due to electroylisis is a concern, but steam pocket formation within the head can ruin it for sure. It just has to happen consistently enough. in the head it happens at a different time than in the waterpump.

 

In higher-pressure applications, water erosion channelling can eat a stainless steel hardened impeller win less than 18 hours of operation significatnly affecting flow!

 

As for an L24 without a secondary external bypass line---no such animal! You may be missing it, but it's there! Even forklifts have it. Some engines are designed with a totally enclosed bypass hole----but the Nissan L-Series, like the Mercedes engine it was originally licensed from, both have dual circuit bypasses. When the secondary line is removed, the only way to insure no cavitation is to slow the pump at idle (larger pulley on pump) and keep the revs low until the thermostat is opened enough to accomodate that flow.

Braap, your observation of the 1/4" hole in the thermostate is probably about the minimum flow requirement so there isn't any problems. (Done by the racing team you mentioned above) this is another method for keeping the minimum flowrate through the pump while the thermostat is closed. Makes the engine slightly slower to warm up, but provides the required minimum flow to allow operation of the engine when cold, and the thermostat is closed.

 

Remember on a racing engine, people aren't starting it cold, and then driving away revving it to 3000 rpms 30 seceonds after the car is started! They will start it, idle it, maybe run it at fast idle to warm it faster, but no revving of any consequence takes place before the engine is at least moderately warmed. The street in this instance is far moreabusive than the track will ever be! Someone starting their car, then driving off and up to freeway speeds within 2 minutes is a prim canidate for cavitation for 30-90 seconds every morning he does it. Now it may take 1000hours of this cavitation to actually perforate a block, or other cast iron component, but a mazak die-casting will get eaten up quite handily under those conditions.

 

My "P" for the "A&P" was completed in 1986, but never finished the second phase of thetraining to get the Airframe certification---so much for "Military Training Opportunities" But afterwards there was more time to do things related to Powerplant Maintenance since I was lead at a 5MW (6.6MW Gross)LFG Recovery Site---when the Steam Turbine end of that project fell through I decided that being in Management and having your project pulled out from underyou was not a position I wanted to be in, so in 93 I traded off to OEM Field Engineering dealing with large stationary Air and Gas Compressors. My SAE subscription lapsed long ago, I really enjoyed the papers to keep up to date with technology and mandates, so that probably answers the rest of the question pretty much, eh? Having grown up in Michigan, and gone to school there, I know many classmates who went to GMI, or ended upworking for hte Big Three, and we kept in touch regarding a lot of stuff---since we all "tread the same water" as OEM reps in many cases, war stories and "inside tales" invariably get brought up. We all laugh at our collective human stupidity (or, probably more correctly, some customer's stupidity! I mean, when I have to field a call from a "Degreed Engineer" who goes off the handle because _this is an actual quote_ "Pump? Pump? WHAT PUMP? NOBODY TOLD US WE NEEDED A PUMP!" Er, Is it a Thermal Siphon? "Huh?" Er, yes, sir, er...you need a pump to provide 2.8 GPM for the heat rejection requirements of the Oil Cooler!)

 

But I digress...

 

Your last paragraph is probably what sums it up the best. As I said above, the drilling of the thermostat is an alternate function of the same thing. Something must allow not only minimum flow for the impeller, but must also allow the thermostat to get sensing the actual heat of the engine. This is one of the reasons I get so upset when people cap that bypass line off---exactly as you stated, if there is only flow through the backside internal orifice, the only way the thermostat gets hot water flowing over it is through conduction! This leads to a bad temp spike on initial startup internally---but rarely shows on the gauge due to reaction time issues. And once the thermostat gets opened, it slams open because of the rush of superheated coolant rushing past it that was resident in the head being recirced...

 

I would venture to guess that 95% of the people who are posting on the topic saying they have no bypass, have made on alternate provision like drilling the thermostat. That your engine builder did this says loads about his understanding about the functions and importance of the minimum flow, and what's required for a quick reacting thermostat.

 

Now, if you want to get into something really interesting, do some research on reverse-flow cooling! Where the coolant flows into the head first, then down the cylinders. Greatly decreases heat temperature, helps with cylinder bore sealing because there is a more even heating of the block, and the thermostat is continually bathed in hot coolant. I was involved in a reverse flow Pontiac Trans Am when I was in School, very intersting results. And curiously Chevy changed the coolant flow in their latest SBC Design. This was based on testing and R&D done back in the late 50's and early 60's, but wasnot widely known or publicized until the mid-late 70's.

 

But again, I digress...

[bjhines]

you have to be kidding.... ALL the front covers I have seen ruined.... were OBVIOUSLY ruined by the ailling/failing waterpumps...

 

cavitation is not what I have seen at work....

 

Funny how a common problem that is obvious to anyone who looks.... is now some sort of astrophysical anomaly caused by removing a useless hose barb.

[Tony D]

Please make constructive commentary from your observations, bj, or make no commentary at all. If you would have read the posts, you would have seen I deliniated the difference between an impeller thrust failure---which is so obvious any moron could diagnose it (case in point)---from cavitation damage which most people do not know about.

 

Nobody said every failure was caused by cavitation damage. Though you seem to imply that the most common cause of overheating is cover damage from failure of the pump bearings "catastrophically" -- causing impeller contact... Funny, I have never had any of my L-Powered vehicles do that---so that says a lot about your maintenance powers of observation compared to mine. (Just something to think about...)

 

Man, you have issues, please sort them out before posting usless barbs and counterproductive things like that last swarf.

[bjhines]

OK... I inspected a couple of front covers.... Tony may be on to something... or it may just be extreme age...

 

There is definitely a possibility of substantial erosion in the raised ring that the blades follow closely.... I found one that shows significant erosion damage... pics to follow......

 

I also have an E31 head that blew through the water jacket into an exhaust port... Which would be a boiling point... I am not entirely sure of the state that some of these parts were run in... stock or not....

 

But these are known issues with these parts under normal high mileage operation.... I would not attribute these to changes in stock cooling flow(more like lack of maintenance)... the E31s are thinwalled compared to other models and this one is full of orange rust and deposites...the eroded front cover is also rusty and caked with grit.

[MikeJTR]

I once bought a Datsun 510 for very little money because of an overheating problem. The owner of the car told me that if the car sat overnight, it would overheat within 10 minutes. But after it overheated the first time, the car would run at normal temperatures for the rest of the day.

The cause of the problem was that the thermostat bypass hose was plugged, and since there was no circulation to the thermostat when the thermostat was closed, the coolant would boil over before the thermostat sensed the hot coolant. After the first boil-over of the morning, the thermostat would open enough to allow circulation, and the car would run fine, until the next morning.

This is an example of temperature spikes that occur in engines before the thermostat opens, and allows circulation through the engine and radiator.

In the older engines, the bypass hose allowed coolant to flow to the thermostat housing so that hot coolant would open the thermostat. Drilling a hole in the thermostat, to allow bypass flow (through the radiator) can eliminate the problem, but the engine takes longer to warm up.

 

Older engines had temperature spikes that would go up and down, until the thermostat stabilized.

If you have a radiator with large tanks that hold a lot of coolant, the temperature spikes of the large volume of coolant going through the engine when the thermostat opens, can cause large temperature spikes, until the thermostat stabilizes.

Modern engines reduce the temperature spikes by using inlet sensing thermostats and small radiator tanks (would hold less coolant).

[JMortensen]

There is another reason behind drilling a hole in the thermostat. I don't think this is a common problem on the L series, but on my Toyota P/U with a 22RE there is a fairly common phenomenon where the temp gets REALLY high, then suddenly drops back down to normal. The problem apparently is that the pressure of the coolant will prevent the thermostat from opening. When it gets really hot, the spring eventually overcomes the pressure, and once the thermostat opens just a crack then it suddenly is able to open all the way, and the temp drops back to normal. The "fix" for this is a double thermostat which has a tiny thermostat facing backwards and then the normal size thermostat in the correct direction. The tiny one doesn't have the coolant pressure fighting it, so it can open, thus relieving the pressure on the normal sized thermostat. OR... drill a hole.

 

So owning the Toy is where I picked up the hole drilling trick. At this point I still have the bypass hose on my Z, but I had intended to remove it. I'll make sure to drill the hole...

[savageskaterkid]

There is another reason behind drilling a hole in the thermostat. I don't think this is a common problem on the L series, but on my Toyota P/U with a 22RE there is a fairly common phenomenon where the temp gets REALLY high, then suddenly drops back down to normal.

 

This used to happen on my old 280zx, then I changed the thermostat and the problem was gone. But back to the topic.

 

Is this bypass you speak of underneath the intake? From how you guys say it, I believe this is it. And with my n/a turbo it seems as though that outlet is hitting the turbo outlet and causing me to not be able to hook up the j-pipe. I was so close, but now I have to take off the manifold again to plug it.

[TONY C]

ok. so the bypass hose is needed or a 1/4" hole has to be drilled in the thermostat.

 

What about the heater hoses? If I wanted no more heater can I simply put a plug in place of the hose connection on the head and in the lower rad hose outlet.

OR.

do I need to route the hose from the lower rad hose outlet to the outlet on the back of the head. simply bypassing the heater core?

what is better?

[DATZ]

On 3/7/2006 at 8:10 PM, briann510 said:

Well I wouldnt argue with Tony on this as for the most part it is there for a reason as he pointed out quite clearly and factually and probably for the average owner should be left intact.

 

I recall asking Tony for advise on this a couple years ago when I bought our Z and it was plugged off because it leaked.

The bypass is there to supply coolant to the intake manifold during cold start ups.   Nissan never installed them in Z’s shipped to Australia.  
 

Tony is wrong and doesn’t know what he’s talking about.