Overheating after exactly 12 miles

Hi all,

It's been a while since I posted here but thought you all might be able to help.

Subject car is a 98 Subaru Legacy. Three days ago it overheated after approx 12 miles of driving. Car had warmed up and was running fine with good heat/defrost, holding engine coolant temp(t-stat working?) just fine. All of a sudden the temp gauge went up - fast. Heater/defrost went cold and it boiled out all the coolant into the overflow. As it cooled it sucked the overflow bottle contents back into the radiator. I topped it off and made it the remaining 3 miles home. I had the thermostat replaced, but the problem is still there. It has repeated this overheating scenario three times now pretty much exactly as described. I haven't done a pressure check or dye check yet but am now suspecting a possible blown head gasket over-pressurizing the system and boiling out the coolant.

Any thoughts would be appreciated.

Thanks,
foureyedbuzzard

So once it heated up it stayed at steddy temp untill it all of a sudden shot up?

So once it heated up it stayed at steddy temp untill it all of a sudden shot up?

First, thanks for the reply. I need all the help I can get. :)

Yes. It warms up quickly, within say three miles or so(small capacity system) and holds steady at normal operating temp as though everything is fine(behaves as though t-stat, water pump, radiator not clogged, electric fans are kicking in fine etc. etc) and then all of a sudden it just goes from mid gauge to pegged in less than a minute and blows all the coolant out through the cap into the overflow bottle. I originally figured it was just a sticking t-stat so I had it replaced. I believe that I'm getting all the air pockets out of the system too when filling it and the fact that it runs fine for approx 10 miles at normal temp seems to eliminate air pockets, cap, etc. I'd expect to see it overheat sooner and blow cold sooner through the heater/defrost if air pockets were the problem. The "weird" thing is that it happens like clockwork. I work seveteen miles from my house and I've pulled over in the EXACT same place off the road each time it happens.

edit: Moving 5 miles closer to work isn't an option(trying to maintain a sense of humor over all this) ;)

I think you have a cracked or warped head, which only opens up the warp or crack when its warmed up, and the metal in the head thermally expands.

Head it by a rad or repair shop and have them run a block check chemical test for head gasket leakage.
It will show any exhust gas in coolant system that can be caused by a cracked head or block or bad head gasket.