a friend of mine has a 1994 wrx, which recently had a rebuild due to a knackered big end shell.
the car has covered approx 2000 miles since the rebuild.
the problem hes having is that the cooling system is pressurising and coolant is back flowing to the coolant reservior in the nearside inner wing.
hes replaced the thermostat and coolant cap to see if they were at fault but its still doing the same thing.
incidently he recently fitted a bleed valve to the turbo a few weeks ago, and i was wondering if upping the boost on a worn turbo could cause the symptoms that hes experiencing?
any advice would be appreciated, thanks.

 

was a new water pump fitted at rebuild? due to age it could very well be worn. Just recently changed mine a few weeks back as mine was worn so badly that the wheel in the pump was hitting the housing so therefore no pumping and pressurizing the system

 

i checked the water pump it seems ok.
does anyone else have any ideas?
thanks.

 

I have recently had the same problem

Turned out when i had a new rad fitted the garage put the return pipe from rad to the header tank and the pipe to the reservior in the nearside inner wing were the wrong way round.

The return from the rad should be the slightly bigger hose of the 2 and it returns into the top of the header tank behind the filler cap.

 

Always recommend to change the water pump when doing rebuilds, my garage (they build full spec rally cars) asked me to include this in the build saying it was a must for a "new" engine.

You could have heat problems from the pump not working correctly which is then causing temps to rise and the cap will then open and fill the overflow tank. It could be another reason for temp problems, but without knowing your engine temps as they are, you're kinda guessing a bit - you cant tell from the oe gauge as its scale for reading hot is a crazy figure, ie its not very accurate. Is there any oil in the coolant?

 

Could be a partially blocked rad

 

Curious to no how much you raised the boost ?