My son just bought his first car, a '90 Legacy L wagon w/EJ22, 180k. Purchased from Subaru mechanic, who claimed to have recently replaced head gaskets and water pump.

 

Car now overheats, but only when driven. It can idle in 100-deg. heat with a/c on for half hour and temp gauge never rises above 1/2 way. Take it out on the street and it overheats within 5 minutes.

 

Have replaced radiator and hoses and I believe we've bled air from coolant correctly. No apparent leaks while car is running, no noticeable smoke from tailpipe. Both fans work. Upper hose is warm to touch, but not overly hot. Radiator cap (also new) is warm as well. Bottom hose feels cooler, but not "cold" after car idles 10 min or so.

 

There does appear to be some condensation in oil, which I know can be bad news. I've read that EJ22s don't typically leak coolant into engine oil..so I'm curious how any liquid would get in there.

 

What would cause car to overheat when driven, but not with extended idle?

 

Any expert recs on what this could be - if not HGs?

You have a few possibilities - clogged radiator, bad thermostat, head gaskets or air in the system - though air usually results in a cold upper radiator hose and tank. Start with the thermostat - replace it with an OEM one or a Stant XACT stat (also OEM). DO NOT use an aftermarket thermostat. That could be part of the problem.

 

GD

Thanks, GD. i have replaced radiator, thermostat and hoses. Bled air from the cooling system (run vehicle until coolant starts to overflow from the bleed valve). CHanged oil and didn't see any signs of water in it. I'm stumped. Hoping not head gaskets, but testing for that is my next step.

i have replaced radiator, thermostat and hoses.

 

So did you install an OEM thermostat?

also, when filling the radiator, try to park with the radiator on the high end of an incline. crack the bleeder screw and fill it until coolant comes out. ENGINE OFF. try burping the hose with your thumb over bleeder screw hole and see if the coolant goes down. do this all with the car cold.

Thanks, Ricearu. I think I've done that correctly, but maybe not. I'll try again. Appreciate your help.

the only reason i repeated it is because you said you ran it while filling until it came out of the bleeder screw, but with the car on, it can push out coolant and fool you.

Ricearu, you are a genius. Took the car to mechanic this morning. He found a "Large air pocket" in the system, removed it. Car runs fine....for now.

 

Thanks all for your assistance!