280z Overheating at low speeds

[sugisan]

I did some more testing in warmer weather (90ish deg).

With just the radiator fans, the temps stabilized at 210 deg F. (In hotter weather, the temps have gone past 210 F)

With the 20" box fan in front of the car, the temp slightly decreased to 205 deg F.

With the hood opened, the temp went down to 195 deg F.

So it seems adding a pusher fan may not help as much in hot weather. There was a lot of hot air coming from under the car with the box fan on. My thought is that the decrease in temp came from the box fan helping remove hot air from the engine bay, not really from cooling the radiator. I think Chickenman is spot on about the pusher fans.

I also read that the pusher fan should be mounted on the radiator for best performance. Since my car has the ac condenser in front of the radiator, I would not be able to do this and won't be as effective.

Also played around with increased idle, but didn't seem to do much.

 

For now, I decided to replace my current radiator fans with Spal ones https://www.summitracing.com/parts/SPU-IX-30101522

Youtube comparison videos of Spal fans had me sold. 

Thank you everyone for the help and I will report back once the fans are installed in couple weeks. 

Edited June 22, 2017 by sugisan

[Slowpoke]

Very curious to see how this goes. I have dual ebay fan setup that i converted to after an IC install. I am becoming more skeptical of these ebay fans... Looking forward to your report on the spal setup.

 

Any way you could report on the amperage draw on your current fans vs the spal?

[NewZed]

 

With the hood opened, the temp went down to 195 deg F.

 

So it seems adding a pusher fan may not help as much in hot weather. There was a lot of hot air coming from under the car with the box fan on. My thought is that the decrease in temp came from the box fan helping remove hot air from the engine bay, not really from cooling the radiator.

 

Don't forget that if the air in the engine bay is just recirculating through the radiator it won't do much cooling.  A lowered car with a front air dam might not allow the hot air to leave.  Your observation about what happens with the hood open is a clue.  Maybe focus on getting the air out from under the car, or through the hood, or access panels.  You might be just spinning your fan blades otherwise.

[Chickenman]

One other thing to check, although this helps more at HWY speeds. Do you have the engine splash shield installed? These often get removed and never replaced. They have an important secondary function and that is to create a low pressure area at the rear of the motor to pull air out of the engine bay.

 

Regarding hood propped open and Temperature drops. That was a common tweak when racing Z cars. Road Racers discovered a long time ago that Z cars built up too much air pressure in the engine bays and that restricted air flow through the Rad. We used to space the hood up by 1/2" to 1" at the rear with rubber grommets ( Sway bar link bushings ) on the  Hood pins. That trick will work at both high and low speeds. 

 

77 and later 280Z's also added functional hood scoops in an effort to reduce engine bay temps. That was to reduce Vapor lock in the fuel rails, but it also bled of high pressure air and allowed more air flow through the radiator. 

 

Pontiac GTP hood vents look nice. Here are some on my Autocross Camaro. These were very effective at reducing under hood pressure and venting heat. 

 

 

 

 

 

 

Edited June 23, 2017 by Chickenman

[Chickenman]

More cooling tweaks. Camaro has an open area between nose of car and rad support.  Air could bypass Rad.  Sides of Rad where already " Boxed in from factory and bottom edge has a scoop to direct air upwards from under car. But they left the top wide open. Dumb. 

 

Sealing this area with an aluminium top plate forces all the air to pass through the Rad.

 

The Carb Air Box was sealed to the hood with a functional cowl vent, and yes it worked very well. 

 

Edited June 23, 2017 by Chickenman

[sugisan]

Very curious to see how this goes. I have dual ebay fan setup that i converted to after an IC install. I am becoming more skeptical of these ebay fans... Looking forward to your report on the spal setup.

 

Any way you could report on the amperage draw on your current fans vs the spal?

I don't have a amp meter for DC current. If you know how I can measure DC current with a cheapo multimeter, let me know.

I'm also curious about the amperage draw because I still have the stock 50amp alternator. 

 

 

One other thing to check, although this helps more at HWY speeds. Do you have the engine splash shield installed? These often get removed and never replaced. They have an important secondary function and that is to create a low pressure area at the rear of the motor to pull air out of the engine bay.

Did not know the Zs came with a splash shield. I will put them on my to do list.

 

I need to look into the vented hoods, but for now, will try to add rubber grommets to lift the hood. I guess getting air out is important as getting air in.

 

Got some work done today. Did some rewiring so that one fan will be operated with a switch and the other fan will be temperature controlled. The radiator and the old fans are out and just waiting for the new fans to ship.

I'll try to make a comparison video between the cheap fans vs Spal fans. 

Edited June 26, 2017 by sugisan

[Miles]

Try a 280z hood. My 240z with SBC and headers creates high engine bay temps. With a 3000 cfm fan you can feel the hot air blasting past the driver's door while sitting at a light as air exits the hood vents. Some people have installed fans under the 280z hood vents.

[NewZed]

 

Did not know the Zs came with a splash shield. I will put them on my to do list.

 

I need to look into the vented hoods, but for now, will try to add rubber grommets to lift the hood. I guess getting air out is important as getting air in.

 

 

 

Seems like you're acting on maybes instead of figuring out the cause first.  You can leave the hood half-latched to do an air evacuation experiment, before installing grommets or getting a vented hood.  And why do they call it a splash shield?  And if Chickenman is right about highway speeds how is it going to help your problem?

 

Don't spend on random possibilities if there's still some simple things you can do to get closer to the true cause.

[Miles]

CFM in = CFM out

[Chickenman]

CFM in = CFM out

 

Exactly.. 

[sugisan]

I'm not sure if this is helpful, but I measured the fans with an cheap energy meter. 

The fans are running off the battery only. Car is not on.

 

Old fan rated at 870 CFM and 10 amps

 

 

Spal Fan rated at 1328 CFM and 13 amps

 

When I test with a multimeter, I'm getting 11.7V at the fans and 12V at the battery. 

I also didn't make the comparison video of the fans... 

Edited June 29, 2017 by sugisan

[TimZ]

It looks like you have a stock engine from your sig - does this mean stock distributor and EFI?  Timing and fuel at low load can make a huge difference in how much heat your engine creates as well.  What is your timing at idle/cruise?

[Tony D]

I got to mention on the Engine Masters that they don't discount the slippage on the Nissan unit. The fan blades are at a governed speed. That is why they come up with a whirr and then stablize flat in pitch and noise. Unless the engine is uphill in the summer towing a load and radiator temps get hot enough to reengage the slip clutch it will not take over a given horsepower....

That said....

Do you still have the 160F thermostat in it? If you are reaching 195, where is this measured and on what kind of gauge?

What PSI is your radiator cap, and what is your glycol/water mix percentage?

In short, with a 3.36 rear  gear, in fifth gear WITH NO FAN WHATSOEVER, running 30 mph, on a 110F Palm Springs Day, your engine  should run 165-170F with a 160 thermostat. If it doesn't your  system is deficient in heat rejection or circulation.

Do NOT loop the heater core. Plug it. Do not let the external bypass line stay open in hot weather.

You  should be able to cool a stock or even hot rodded engine of 250 hp with a standard three core copper and brass radiator. The biggest thing you can to to suppress nucleate boiling is to run a higher pressure cap. 16 is a minimum, but a 24 or 30# cap will keep the steam from forming pockets and causing a runaway overheating issue.

Now, you state 'overheating' but 220 is warm...not necessarily overheated. You need to specify which thermostat you have as the temperature at the back of the head will be 15-20F higher than  what you sense at the thermostat outlet at the front of the engine. This is why the back cylinders detonate so often.

Most curious on where the temperatures are coming from...either I missed it in reading the thread, or it hasn't been mentioned. 

[Tony D]

Oh, and if the thermal switch is turning your fan on later than 175F, its likely too late. If you have read my prior posts on e-fan setup, the above test to determine slowest speed stable temp you get on a hot day dictates where your fan turns on so it's  not running while going down the freeway or even in city streets. It will only come on in  stop and go and come on early enough to prevent nucleate boiling from starting and becoming a problem. I set mine to turn on 10F above where my temperature  stabilized  on that 110F day, right around 175. I could see the temp rise on the stock gauge, hear the fan kick on and watch it go back to lower temperature then shut back off. Cycled nicely in stop and go, and has since 1990!

[sugisan]

Small update after installing the Spal fans: Been driving in 90 deg weather with some stop and go traffic and the fans are doing a better job at cooling the car. When the fans kick in, the temperature actually comes down even when idling and with the AC blasting. Previously, the temps kept climbing with the fans on and no AC. So far so good. I have yet to test in 100+ weather and I have an autocross coming up in couple weeks so I'll update again after that. 

 

 

Do you still have the 160F thermostat in it? If you are reaching 195, where is this measured and on what kind of gauge?

What PSI is your radiator cap, and what is your glycol/water mix percentage?

In short, with a 3.36 rear  gear, in fifth gear WITH NO FAN WHATSOEVER, running 30 mph, on a 110F Palm Springs Day, your engine  should run 165-170F with a 160 thermostat. If it doesn't your  system is deficient in heat rejection or circulation.

Do NOT loop the heater core. Plug it. Do not let the external bypass line stay open in hot weather.

You  should be able to cool a stock or even hot rodded engine of 250 hp with a standard three core copper and brass radiator. The biggest thing you can to to suppress nucleate boiling is to run a higher pressure cap. 16 is a minimum, but a 24 or 30# cap will keep the steam from forming pockets and causing a runaway overheating issue.

Now, you state 'overheating' but 220 is warm...not necessarily overheated. You need to specify which thermostat you have as the temperature at the back of the head will be 15-20F higher than  what you sense at the thermostat outlet at the front of the engine. This is why the back cylinders detonate so often.

Most curious on where the temperatures are coming from...either I missed it in reading the thread, or it hasn't been mentioned. 

 

I do have the 160 deg F thermostat. The temperature was taken with a cheap infrared thermometer at the base of the external bypass line. It was where I was measuring the highest temp in that area so all the temps were taken from there during testing.

The radiator caps has a 0.9 stamped on it, so I'm assuming 0.9 bar or 13 psi. Currently using the premixed 50/50 anti-freeze (have not added any distilled water). I did add a bottle of water wetter several months ago.

Where should the coolant level be in the radiator? It is currently at about 1" below the top of the radiator (top of the actual radiator, not the cap).

Can you explain why I should plug the heater core. 

For the external bypass line, are you saying to completely plug it in hot weather or have some sort of valve to close the line when the water temp gets hot.

If you have already explained this in a different post, I can search it.

 

I'm not sure about 110 F and 30 mph, but at around 95 F and 40 mph, the temp gauge stays right in the middle and the fans do not turn on. I know 95 F / 40 mph is not even close to 110 F / 30 mph, but that's what I have been able to examine so far.

 

Oh, and if the thermal switch is turning your fan on later than 175F, its likely too late. If you have read my prior posts on e-fan setup, the above test to determine slowest speed stable temp you get on a hot day dictates where your fan turns on so it's  not running while going down the freeway or even in city streets. It will only come on in  stop and go and come on early enough to prevent nucleate boiling from starting and becoming a problem. I set mine to turn on 10F above where my temperature  stabilized  on that 110F day, right around 175. I could see the temp rise on the stock gauge, hear the fan kick on and watch it go back to lower temperature then shut back off. Cycled nicely in stop and go, and has since 1990!

The thermo switch I'm using now is 185F on/175F off. 

 

It looks like you have a stock engine from your sig - does this mean stock distributor and EFI?  Timing and fuel at low load can make a huge difference in how much heat your engine creates as well.  What is your timing at idle/cruise?

I replaced the stock distributor with one from Autozone (direct replacement of stock) and modified the trigger to work with the MSD ignition (previous PO modified the ignition system so I'm not very familiar with it). The timing is set stock timing according to the manual.

Edited July 12, 2017 by sugisan

[Chickenman]

Sounds like you've got things handled nicely. 

 

Question on AC. Did you find that the new fans made the AC blow any cooler when stopped and at idle, compared to old electric fans?

 

That's the only issue I have with my stock 1976 280Z fan setup and my AC. No Air flow through condenser at idle. Water temp stays fine, but AC starts blowing luke warm. As soon as I start moving, AC blows freezy cold.   

[sugisan]

My car is the same. Half of it is probably because the AC compressor isn't turning fast enough to adequately compress the refrigerant. My idle drops 200 rpm to 600 when AC is on. I just gas it to around 1500 rpm when I'm stopped at a light for colder air.

I can't say that the new fans help because I used to turn off AC during idle with my old fans to help with overheating. Stop lights weren't fun...

My old civic and my current 2013 Mazda2 also blows warmer air at idle. I'm just happy I have AC in the Z

[Chickenman]

 

Where should the coolant level be in the radiator? It is currently at about 1" below the top of the radiator (top of the actual radiator, not the cap).

Can you explain why I should plug the heater core. 

 

A 280Z should have a factory Coolant recovery tank. Coolant level should be all the way to the very top. Otherwise the recovery Tank will not work. Coolant recovery tanks help reduce over heating by eliminating air pockets or steam pockets. 

[Powerglide]

Not braggin... And I can't tell you why. But my 76 EFI Z has cheap eBay radiator. 180 degree thermostat, a header (under stock Heat shield), a/c with a Sanden 709 compressor that's always running in our south Florida July heat STRUGGLES to get over 185. That's even after a 15 mile cruise at 80 mph and stopped at a traffic light for 4-5 minutes. It's got the ORIGINAL Paraut fan clutch and a 50/50 ratio of regular old yellow Preston. Thing is...the hotter it runs---the better it runs! I've run 190 thermostat, even here in summertime. But it doesn't seem right, and the extra latent heat inside the car is a REAL challenge to cool. Even with R12. And a 3 or 4 hour heat soak after a hot shutdown will WORK any cooling system or A/C system.

 

Oh, and prior to installing it in my garage. I sprayed it with a light coat of Krylon semi-flat black purely for the cosmetic value. That should REDUCE heat transfer somewhat.

Edited July 14, 2017 by Powerglide

[TimZ]

Can you explain why I should plug the heater core. 

 

Some people remove/disconnect the heater core, usually in an attempt to make a lightweight race car, or to remedy a malfunctioning/leaking heater core or leaking interior hoses.  For some reason many who do this decide that it would be a really good idea to connect the two water lines for the now missing heater core together to make a loop.  To make a long story short it isn't a good idea.  

 

Tony and JeffP actually went to the trouble of proving this via instrumented, controlled testing on an engine dyno, and STILL the idea won't die and people loop the heater core lines.

 

If you still have the heater core in the system, then this should not apply to you.

Edited July 22, 2017 by TimZ