HELP: Random overheating making me get crazy

[THUNDA]

hi all

my new subi started overheating yesturday - (ARRRGG PHUK!)

so i ripped into it

Lower radiator main hose was leaking - so i Replaced it

Car ran fine for about 20mins of driving

Then car starts overheating again

Radiator Resivour starts leaking from around the sides (i know these resirvoirs suck from previous experiences) - so I replaced it (with the BD5 metal one)

Can ran fine for about 20mins of driving

then car starts overheating again

Look for the leak- find its under the intake manifold, some plastic 3way joiner pipe is leaking - cant get to it but dont think there is much point in replacing it if its just gonna pop another pipe - car doesnt overheat at idle either, it happens when the turbo is being used / your pushing the engine.

i replaced thermostat

Checked waterpump is cycling (it is)

Checked radiator for blockage (its not)

My guess is head gasket is leaking between combustion chamber and water galleries - forcing alot of pressure into the cooling system thus popping pipes

what are your guys thoughts?

ive had this happen before - but i could tell it was this because with the radiator cap off the car wouldn't overheat and you could see the steem pulsing out of the reserviour at the same rate as the "bop bop bop" subi noise at idle. but this time it doesnt do this...

[Drunkenmonkey]

is it fulling up the over flow, when my head gasket went it was pushing all the water out the over flow

[Swindog]

Have you bled it?? Maybe an airlock.

[Max Headroom]

It might sound weird, but if the heater matrix is blocked, it can cause the thermostat to stay closed and give the symptoms of HG problems. Happened to me. Easy way to check is to place a hand on each end of the radiator next time it overheats. If the thermostat is still closed, the radiator will be cold at the thermostat end and hot at the other.

Either replace the heater matrix (big job) or fit a bypass hose between the heater hoses to allow the coolant to circulate around the heater matrix.

It's worth checking, could save you a lot of grief and expense . . .