Hey guys, I just got my car back from the shop where they installed a new Koyo radiator. The problem is that when the car is sitting or stopped at a stop light the heat blows cold air. When I start going again the heat starts to warm up again, but when I stop it goes back to cold. Is it supposed to do this or do i have a problem with my heater core?

Thanks,
Vince

 

sounds like you are going to have to change thermostats. that one too cool since the radiator replacement ..

not positive but what it sound like to me

 

Really? Its the stock thermostat. I didn't replace it with the Nismo one. Maybe its just cause I live in the armpit of the world here in Cincy. So I guess I just might have to live with this crap.

 

now that i look at your post again i dont think that what i stated is the problem. i mis-read what you were saying. im not sure what the problem is

 

Anyone else care to take a whack at what the problem could be?

 

you probably have air in your cooling system. need to bleed out the air.

 

I would bet that the problem is that the coolant is too low.

 

+1. The cooling system for the VQ35 is notorious for being a biatch to bleed. You think it has no air pockets and two weeks later the chit comes back. You can take it to the dealer. They have some special tool or something. It is like $80 though.

 

Its probably going to be your thermostat. Mine started by doing that, we bled the system then eventually the thermostat wouldn't open. Watch the engine temp and make sure it doesn't get to high if it does change the thermostat. Im on my 4th one.

I had a stock before turbo kit.
Changed to Nismo on turbo kit.
18k miles on turbo kit bought another nismo
Just yesterday I replaced it with another stock one. We'll see how it goes.

 

that sucks! I replaced my stock with the Nismo after installing my PE radiator. About two months later it overheated and I thought I had bubbles. Never investaged the termostat cause I had other problems with the motor.

This is not the 1st time I hear of someone having to replace several thermostats. I think I am just going to remove mine. It doesn't get that cold in Miami anyway.

How do you test the thermostat to see if it is not working?

 

Im not a mechanic but i'd assume by what the OP said. That may be a sign but not tell tale. Or if your engine temp gets really hot and then eventually it opens up and you see the temp fall real quick i'd say thats a sign. Cool air coming out when engine temp is already normal. Those are at least the signs i saw, also it wanted to stall a lot more.

 

So the general consensus is that I either have air in the cooling system or my thermostat is a POS. Well at least I have something to go check. Thanks for the help guys, I will let you know what the outcome is.

 

it's likely an air issue- it can very often mask itself as a thermostat issue

 

My water temp gauge functions just like normally, no fluctuations. I am taking it back to the shop on Friday under the assumption that their is air in the cooling system that needs to be bled out. Thanks for everyone's help!

Vince

 

It is true that the z33 can be a ***** to bleed the cooling system. In order to get all the air out of the system, fill up the radiator and cap it off. Then take the plastic bleeder screw out of the heater hose and fill from there as well. Get in the car and start the engine, run the heater full blast and hold the rpms at 3000 until the engine is up to temp and the heater blows hot. Wait for it to cool down and repeat as necessary.

 

It is true that the z33 can be a ***** to bleed the cooling system. In order to get all the air out of the system, fill up the radiator and cap it off. Then take the plastic bleeder screw out of the heater hose and fill from there as well. Get in the car and start the engine, run the heater full blast and hold the rpms at 3000 until the engine is up to temp and the heater blows hot. Wait for it to cool down and repeat as necessary.

A dead giveaway for a bad thermostat is when the engine is up to temp and one radiator hose is not hot.

 

The thermostats on this car suck. Both stock and Nismo. I had a similar issue to barthelb. Had stock one...it stopped opening. Replaced with another stock. 2 months laters..same thing...I finally just pulled it completely. Haven't run a thermostat in 10k miles now. My water temps went from 195-200 when cruising to 180-190. Under hard driving water temps is around 195-200. Highest it ever got with no thermostat was at Cal Speedway running the car HARD it was 105 outside and my water temp was 205.

 

Holy crap! Is that safe? Could it damage the engine doing that?

 

It hasn't on my last two cars but people will say it could potentially cause damage to the water pump due to less restriction not preventing cavitation at the pump, or that the water will not cool as well cause its flowing faster (obviously not true), but "they" say a lot...it works for me..

 

Just got back from the shop and the problem is fixed....i hope. Heat works now and the temp gauge is steady. They called nissan to find out how to get the air out of the system and it goes a little something like this......

Lift front end of car (very important)
remove radiator cap (make sure car is cool or you get spewage)
start car
run at 1500rpm for 10-15 mins with full heat blowing
replace radiator cap
lower vehicle
your done!

I believe this is exactally how he explained it to me. He also said that nissan did not have a special tool to do this, they just follow the procedure above.

Thanks,
Vince