Not quite overheating

[chaseincats]

1 minute ago, Mark Maras said:

 Almost right. Along with spinning the pump and fan faster you're also running the engine faster which means more heat is created in any given length of time than it would at idle. Out of curiosity are you using a fan shroud?

Gotcha, so I shouldn't expect the temp to drop if I do that then?

Yep, I have the shroud

[Mark Maras]

2 hours ago, chaseincats said:

Gotcha, so I shouldn't expect the temp to drop if I do that then?

Yep, I have the shroud

 That depends on coolant flow and air flow. A temp drop isn't a sure thing if either of the others isn't up to snuff.

 A long time ago the fan clutch on my 71 locked up. I ended up replacing it with a flex fan and a spacer to put it about 1/2" from the rad. (Not a popular replacement for most Z owners). I ran it for another 15+ years and found it to be superior to the fan clutch. 

[chaseincats]

Update for you guys.

I spoke with my old Z mechanic and he said (and I've heard from a couple folks on Z forums too) that aftermarket thermostats don't flow as much coolant as an OEM one.  Has anyone else here heard of this or is it more of a wives tale?

I took my old Nissan OEM thermostat and popped it in a pot of water and the 170 degree thermostat didn't start opening until 185ish so I'm guessing that was bad and the new one which is aftermarket isn't large enough to flow enough coolant for a steady temp.  Can anyone recommend a 170 degree thermostat that flows as much coolant as an OEM one?

Currently the thermostat I have is this.

[Zed Head]

Just remove it and see if the system can cool things down.  The engine should never get up to operating temperature without a thermostat.  If it can't keep things cool then it won't matter what thermostat you have in there.

p.s. the thermostat is actually a heating device.  It blocks coolant flow until the coolant reaches desired temperature.

Edited November 18, 2022 by Zed Head

[chaseincats]

On 11/18/2022 at 3:20 PM, Zed Head said:

Just remove it and see if the system can cool things down.  The engine should never get up to operating temperature without a thermostat.  If it can't keep things cool then it won't matter what thermostat you have in there.

p.s. the thermostat is actually a heating device.  It blocks coolant flow until the coolant reaches desired temperature.

I'll give that a shot, thanks!

Has anyone tried this thermostat in a world where the OEM one is NLA?

[Racer X]

50 minutes ago, chaseincats said:

I'll give that a shot, thanks!

Has anyone tried this thermostat in a world where the OEM one is NLA?

Forty five bucks for a thermostat?

Buy one at NAPA. About $10.

I can guarantee that your classic Z won’t know the difference.

Used a NAPA thermostat on engines in my race Z, never had cooling system troubles. (I must say that when running hard, as during a race, the oil system needs a cooler, as the oil also carries heat away from the engine.)

Edited November 20, 2022 by Racer X

[chaseincats]

1 minute ago, Racer X said:

Forty five bucks for a thermostat?

Buy one at NAPA. About $10.

I can guarantee that your classic Z won’t know the difference.

 

I've heard from a bunch of sources that the smaller opening of the aftermarket thermostats compared to the OEM one (and apparently now this) hinders cooling.  That's the case at least (probably) on my car.

[Racer X]

8 minutes ago, chaseincats said:

I've heard from a bunch of sources that the smaller opening of the aftermarket thermostats compared to the OEM one (and apparently now this) hinders cooling.  That's the case at least (probably) on my car.

I saw that comment earlier.

But as Zed pointed out, the thermostat holds coolant flow back until the system reaches operating temperature.

If the engine is running too hot, it is likely a problem with the radiator, the smaller cooling passages in the cylinder head, or the impellers of the water pump eroded from electrolysis. (I have seen water pump impellers eroded to nearly nothing as a result of poor cooling system maintenance.)

 

Edited November 20, 2022 by Racer X

[chaseincats]

1 minute ago, Racer X said:

I saw that comment earlier.

But as Zed pointed out, the thermostat holds coolant flow back until the system reaches operating temperature.

If the engine is running too hot, it is likely a problem with the radiator, the smaller cooling passages in the cylinder head, or the impellers of the water pump eroded from electrolysis. (I have seen water pump impellers eroded to nearly nothing as a result of poor cooling system maintenance.)

 

The car has a new radiator and water pump and before I did that, I flushed out the rust (in theory) with the radiator flush chemical a few times and did the old 'hose in the thermostat housing' routine.

[Racer X]

12 minutes ago, chaseincats said:

The car has a new radiator and water pump and before I did that, I flushed out the rust (in theory) with the radiator flush chemical a few times and did the old 'hose in the thermostat housing' routine.

I just went through the whole thread, and see all the stuff you have done. The only two things that I don’t see that haven’t been done, and should have been done first, is a system pressure test, and check the radiator cap for pressure.
 

Use a cooling system pressure tester to pressurize the system and then watch to see if it holds pressure. It can also be used to check the radiator cap. Local parts stores rent them if you don’t wish to purchase one. I have found two at garage sales for a couple of bucks.

If there is a loss of pressure, the cause needs to be found and corrected. Sometimes it is simply a loose hose clamp, but it could also be a failing head gasket.

There has been discussion about the boiling point of water, and the boiling point of the coolant mixture, but no one has mentioned that the boiling point is raised buy increasing pressure in the cooling system. I forget the precise numbers, but that is the function of the radiator cap, to increase pressure and raise the boiling point. This helps the coolant to carry the heat to the radiator, which then dissipates the heat befor the coolant is returned to the engine to collect more heat.

Also, are you using ordinary tap water, or distilled water. Tap water will have minerals, and even worse in your area, iron. This leads to excess scale and rust in the cooling passages, and contributes to electrolysis.

[chaseincats]

8 hours ago, Racer X said:

I just went through the whole thread, and see all the stuff you have done. The only two things that I don’t see that haven’t been done, and should have been done first, is a system pressure test, and check the radiator cap for pressure.
 

Use a cooling system pressure tester to pressurize the system and then watch to see if it holds pressure. It can also be used to check the radiator cap. Local parts stores rent them if you don’t wish to purchase one. I have found two at garage sales for a couple of bucks.

If there is a loss of pressure, the cause needs to be found and corrected. Sometimes it is simply a loose hose clamp, but it could also be a failing head gasket.

There has been discussion about the boiling point of water, and the boiling point of the coolant mixture, but no one has mentioned that the boiling point is raised buy increasing pressure in the cooling system. I forget the precise numbers, but that is the function of the radiator cap, to increase pressure and raise the boiling point. This helps the coolant to carry the heat to the radiator, which then dissipates the heat befor the coolant is returned to the engine to collect more heat.

Also, are you using ordinary tap water, or distilled water. Tap water will have minerals, and even worse in your area, iron. This leads to excess scale and rust in the cooling passages, and contributes to electrolysis.

 

Good catch, I should have added that I did pressure test the cooling system and radiator cap when I installed all of that new hardware a few months ago.  I also did a leak-down test yesterday and besides finding out I have a few tired piston rings, I confirmed there isn't any combustion gas leaking into the coolant.

[chaseincats]

UPDATE: I spoke with my old Z mechanic to see where he got the OEM thermostat that was in the car before my changeover to the new aftermarket one earlier this year since OEM ones are supposedly NLA.  It turns out Nissan still makes a thermostat that works but is not the original one designated for the car.  This thermostat is a Nissan part (part number 21200-F3190) but works in a bunch of their engines (L-series included).  This is the thermostat that held the car's temperature at 170 from 2015-2020 before I started having cooling issues.

I threw the old and new OEM thermostats as well as the aftermarket one in a pot of water.  The old OEM thermostat started opening at 185 (unlike the new OEM one which opened around 170) and after continuing to heat the pot, the old OEM thermostat only ended up opening about 2/3's as much as the new OEM thermostat so the old OEM thermostat was indeed bad.

The aftermarket one opened and closed at the same temperatures as the new OEM thermostat but the opening indeed is about 30% smaller than the OEM thermostat and the amount of travel the plunger can physically move is again maybe 30% less due to it being physically shorter.

I have not tried the new thermostat in the car because driving it around in this cold weather won't give me a definitive answer, but I am feeling confident that my old worn-out OEM thermostat not opening at the right temperature (and not to the right amount) started this issue, and installing an aftermarket thermostat that physically can't move as much coolant as an OEM one kept me heating up, but for for a different reason entirely.  With the new OEM thermostat correcting both issues, we should be all set come spring time.

Here are pictures of the OEM one (right side) next to the aftermarket one (left side).  You can see the opening is considerably smaller and plunger's travel is considerably shorter on the aftermarket unit.  I will update you guys in the spring.  I don't understand how/why they sell this design...

Edited December 12, 2022 by chaseincats