i have a 07 sti 32k i had a head gasket fail before so i got the engine rebuild and forged with upgraded heard studs and cosworth head gasket and the blocked pinned 3 years ago cars running 420bhp and 420lbft mapped by jgm a few weeks ago now it has started overheating again then the car running the heater in the car is running cold i bled the system for air locks then i was bleeding the car started to overheat i rev the car to 3.5k and the temp dropped and the heating started to work need help working this out if i need a rebuild or it has a air lock or need a thermostat please help thanks

 

May we'll be HG failure but I'd rule out the obvious first. Airlock is a common one but easy to resolve. Make sure there are no leaks & check the thermostat too, water pumps don't usually go but worth checking too. Everyone goes on about doing a block test with the blue dye, worth a go I suppose but in my experience they rarely work on impreza engines, both times my HG failed the dye stayed blue telling me all was OK when it wasn't.

 

What's the best way to remove an airlock? Burp it from the header tank nearest the turbo? Fast idle?

 

I'd empty the system & start again filling very slowly while squeezing the bottom hose. Once full leave on tick over while squeezing the bottom hose again. Top up header & expansion tanks refit caps & gently drive until up to temp, then park up until totally cold & top up again as the level often drops.

 

Have to ask yourself why it developed an air lock in the first place.

You either have a leak or the HG have gone again, in my layman's opinion.

I would pick up the phone to the engine builder as three years and 32k (less if you include the mileage when it first went pop) is not within the kind of time frame you'd expect to have issues again.

 

But that could all depend on the head gasket used more so as its been mapped a few weeks ago and as i assume it may have had the boost upped alittle and brought forward an underlying problem with the quality of the head gasket itself (not at all putting simon to blame as his knowledge is A1)

 

What uprated headstuds?

 

+1

 

Water pump,thermostat?.

 

Check for leaks, maybe there is a leak and you where low on water...
I regularly check the water, oil and other fluids in my WRX after a HG failure when top rad hose gone.

 

Did you sort it?.