1990 Toyota Celica GT4, Coolant is boiling and spurting out, Temp gauge is normal

[ciron56]

Hi All,

I recently got a GT4 Celica and have encountered an annoying issue.
Whenever you push the car a little bit and boost, when you stop the car and take out the keys, the radiator and the overflow is boiling (bubbling) and spilling out.
Driving the car without boosting, the issue doesnt seem to happen.
The temperature gauge is saying that the car is not overheating .
I am pretty sure the temp gauge is working as the car did overheat when i first got it because the rad was empty (had no water or coolant in it).
The radiator is aftermarket (im not sure what brand or anything) and was put in by the last owner. The thing has all custom piping and is so large that the battery was relocated to the boot.
Im pretty sure it is not a head gasket issue as the coolant coming out is really clean, there is no gunk on the radiator cap and the car drives perfect other then this issue.
Does anyone have any suggestions on what it can be or any tests i can do?
I have tested the water pump and that appears to be working.
Im going to get a new radiator cap and thermo to see if that fixes it and try to do a coolant flush incase there is any air in the loop causing the issue.
Thanks so much!

Ciaran

[masterofsinanju]

Hate to say it but sounds like head gasket. It is possible if you a running standard bolts in the head, that boost is lifting the head enough to pressurise your coolant. Heag gaskets can fail in a number of ways that do not necessarily allow mixing of oil and coolant.

Try a tk test. That will tell you if exhaust gases are passing into the coolant.

[Cuts]

Sounds like a head gasket. I had a similar issue in my 205. Basically it's not blown you just get some leaking of combustion into the coolant system, it pressurises it and blows coolant out the overflow. But it doesn't let coolant back in so you don't get the cheese under the cap.
Head off, check head for flatness and deck if necessary, screw it back down tight and you're done.

[ciron56]

Great, thanks so much for the help!
Ill get it tested asap!