Hi all, I was hoping someone could give me a second opinion on whether my head gasket has failed as the symptoms seem inconclusive.

I've got a 2003 GD WRX that I've owned from new (yes really). The car started blowing cool air rather than warm whilst in traffic and then over heat. My local Subaru guy tested the head gasket but it was inconclusive and there is no white smoke, milky oil etc however he did see bubbles in the expansion tank. The car was flushed through and sealant added, and the thermostat replaced along with the header and radiator caps.

I've just taken it for 2 test drives. The first was the same as before i.e. the temperature gauge was fine whilst moving but started going up on the way home when sat at lights. After a bit of googling I did an experiment and did the same drive again but with the AC on and max fans and temp. This time the temperature remained fine however as soon as I turned off the AC (but left the fans and temp on max) the temperature started rising. The coolant seems stable but I've only done about 20 miles.

I'm not sure a HG replacement will be financially viable however after 22 years of ownership I feel I owe the car every chance of redemption before I have to take drastic action. Does anyone have any thoughts on potential solutions aside from HG replacement?

Thanks

 

I'd be checking radiator cooling fans: A/C overrides cooling fans. Turning off A/C will rely on them triggered by coolant temp alone.

Also I would not use the factory gauge to verify temperature: They have a huge dead band (as in big temperature difference =no gauge movement). Live data from the OBD port is far better. Failing that a laser thermometer on the engine block and heads, heater hoses etc. (beware chinese ones aren't that accurate).

How specifically did garage check the HG? Gas analyser for combustion gases? Indicator Dye tester (Uview tester)?

HGs usually rarely cause oil/water mixing or smoke in this day and age. They are more likely to go porous due to corrosion (old coolant+time, especially if not routinely changed) or very slightly lift/weep between the combustion chamber and water jacket when under load; First signs are indeed air locks and intermittent loss of heater output. It's only when they've been cooked in a major way (i.e overheat, then carry on driving whilst overheating )do they pop and mix fluids and smoke.

 

Thanks for the reply.

If it is the fans then I see 2 potential possibilities. 1/ The sensor is broken and the fans are not turning on when hot. 2/ The sensor is OK but some other issue (air lock due to HG) means it stays cool and so never activates.

For 2 is it possible that an air lock prevents the coolant around the sensor heating up?

Also, I think they used a gas analyser to test the HG but not sure, will check.