I'm stumped!

I had the cooling system pressure tested and was told there was no signs of combustion in the cooling system but they did notice some bubbles.

The issue: Only after boost, my car will overheat. Trying to diagnose this issue, I've removed the coolant lines I had going to the turbo and put back to stock heater hose configuration. Removed the rest of my a/c stuff and switched my fans to "pushers". Water pump was new when I built the motor and probably has no more than 10k miles. I also recently installed a N1 water pump pulley (from Gspec) and a turbo blanket.

I notice that, after boosting, the car tends to push coolant out the overflow tank and an air pocket will eventually make it's way behind the thermostat. I can stay out of boost and it doesn't seem to overheat...drove for 2hrs with no issues w/o boost.

There are no visible leaks and no oil in the coolant or vice-versa.

I can't figure out why coolant is getting pushed out or where the source of air is coming from.

Any help is greatly appreciated. Car is a '91 SE-R with an extensive mod list.

sounds like a head gasket.....

if you take the rad cap off and jerk on the throttle cable does it shoot a lot of coolant out?

That's what I originally thought but when the cooling system was pressure tested a die was added to check for combustion in the system...none found.

I dunno.

That's what I originally thought but when the cooling system was pressure tested a die was added to check for combustion in the system...none found.

I dunno.

Just for luck... Have you tried changing your radiator cap for a new one? Sometimes they came a little bit loose on their sealing part and you get also those kind of results--

this might be a long shot but i would take a look at the coolant temp sensor or thermostat also do you have a upgraded radiator

Just for luck... Have you tried changing your radiator cap for a new one? Sometimes they came a little bit loose on their sealing part and you get also those kind of results--

this is very true upgrade to a z32 rad cap

The die tests aren't always truthful. It usually has a little canister you sit on top of the radiator and you add the die and if it changes color while the car is idling there are combustion gases present. Sometimes the car has to be under a load and that's hard to do when standing still.

A new radiator cap is a whole lot cheaper and easier than a head gasket.

Head gasket.

I've tried three different caps...car has the NISMO radiator which I believe is just a 2 row vs 1 row stock, and replaced the t-stat trying to diagnose this issue...old stat is still good.

this might be a long shot but i would take a look at the coolant temp sensor or thermostat also do you have a upgraded radiator

What would I be looking for at the coolant temp sensor?

The die tests aren't always truthful. It usually has a little canister you sit on top of the radiator and you add the die and if it changes color while the car is idling there are combustion gases present. Sometimes the car has to be under a load and that's hard to do when standing still.

A new radiator cap is a whole lot cheaper and easier than a head gasket.


I wondered about this....bubbles at idle could very easily be much more air at higher boost levels (12-18psi)...I need to revisit the 'leak down'.

Are you using stock head bolts or studs? If you have studs, you might try retorquing them. That solved a pretty much identical issue for Cliff:

http://www.sr20-forum.com/turbo/28198-general-consensus-lifted-head.html

I have OE head bolts...and am considering switching to studs...mainly b/c I'm second guessing myself on the OE head bolts. I'm feel sure I would've used brand new head bolts but for the life of me can't remember.

I have OE head bolts...and am considering switching to studs...mainly b/c I'm second guessing myself on the OE head bolts. I'm feel sure I would've used brand new head bolts but for the life of me can't remember.

Because of related problems in the past, I switch to ARP head bolts.. no problems so far.. now I am installing rod bolts :P

bolts? not studs?

I'm gonna just try and retorque them to the high side first.

sounds like a leak from the head gasket

i had the SAME exact problem.. headgasket lol

I'm feel sure I would've used brand new head bolts but for the life of me can't remember.

You did use new head bolts.

I had the same problem, head gasket