KA OVERHEATS

[Romeo_rus]

Hi! Definately need some help, I'm a mechanic, but I do not understand what happens and I need some help... So I recently bought a 240sx stock, auto.. and It didn't have a thermostat in it, so I assume the previous owner of this car fought with the same problem.. well lets begin with description
1. I installed a new water pump, new (autozone) thermostat, new 12'' electric fans
2. When the did not have thermostat - IT DID NOT OVERHEAT
3. Fans work fine
4. The car overheats ONLY after some driving (40 miles to work) at stops... So when the car moves it does not overheat, when I stop - starts overheating
5. Did radiator cleaning, radiator flushes - I know how to do it (this is my 10th 240...raise 240's nose up, unscrew the bolt on top of upper hose ect)
6. after it starts boiling I shut my car off let it cool down/or after work I let my car idle for an hour - does not overheat, drive around a block, stop/idle - overheats
7. compression test - 135psi all cylinders
8. leak down test - no leaks, no pressure drops
9. when the is boiling - the lower rad hose is cold
10. no water/coolant in oil
11. no oil in coolant
IF you dont have any suggestions, by the next week I call exorcist...

[moso]

get rid of the cheap thermostat and use a genuine nissan one. the opening is almost always bigger on the nissan one than the cheapies, even stant thermostat openings are smaller. i cant guarantee that is gonna fix the problem but its a good start.

[scotty-2-forty]

Are you certain the electric fans are working and/or hooked up properly? I had a similar problem with my twin Flex-a-lites whereas in my case the motors burnt out. The car was fine on the highway with a good flow of cool air, but when coming to a stand-still or an idle the temp went up and I had to shut it down. Ditched the elecs and went back to the clutch fan ... no problems. Just a thought on top of the thermostat comment.

Also, you might have a blockage in the coolant passage somewhere and/or air pockets. I know you said you flushed it, but blockage might not break-up in a flush.

[hoffmanestates]

lol. i am in the same boat. world is small i see. but i dont have electric fans. i just purchased a OEM thermostat paid 25$ and getting a OEM water pump its $100 im sticker shocked but w.e it seems like a symptom of thermostat. unless the last owner used raiator sealant and thats bad.im going to run shop air through my passages and see if i get anything out the other end along with the radiator.

[JKL1031]

could be a leak at the head?

[Romeo_rus]

I started guessing that it might be a head gasket, because when I open a bleeding bolt when the car is running only bubbles are coming out, when the car is turned off - clean and pure coolant... I guess it might be exhaust gases... (((( if I won't find a solution there will be 2 choices KA reBIULD or rb20 swap ((((

[JKL1031]

yeah to think of it, when i gave it gas, the steam was rev related. I know at the same time the water pump is turning faster, but the height and flow of the steam column coming out was proportional to the engine speed.

[OutToWinPAHC]

1 - Stop driving it
2 - Rent a cooling system pressure tester from a loan a tool. Test the system at 1.3 bar and see if it holds pressure.
If it holds pressure, or you find a leak and repair it then...
3 - Replace T-stat with the hole facing up, replace radiator cap with a Nissan cap.
4- Properly bleed the cooling system

[hoffmanestates]

good idea or find a guy with a coolant refill tool. you will need an air compressor as it use's a venturi way to put your coolant system under a vacum. it puts your whole coolant system under a vacum like 13lbs as the rad cap says you disconnect air and wait for like 5min to see if the vacumm is diminishing. if not stick the refill tube into bucket of premix and prime the tool. put a vacum on again for 13lbs disconnect air and flip the switches and the vacum sucks in the coolant. removing the dam :air pocket: behind the T-stat. i know it works on semi diesel, anything from cummins detriots ect.... excepet those are abour 15lb systems . anyway i have one locally in chicagoland if need be., with compressor.