Overheats after EXACTLY 12 miles every time

Also posted in "Cars in General" forum

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.
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.

Any thoughts would be appreciated.

Thanks,
foureyedbuzzard

What's coming out the exhaust, any excessive moisture?

Definitely check the head gaskets, it sounds like you could have a blown gasket, better check now while it's a 'minor' issue.

I agree with the blown head gasket. Had the very same thing happen on my Legacy. I never checked the miles but 12 sounds about right. No water ever showed in the oil. Had the head gasket replaced and the car's been running fine ever since.

What's coming out the exhaust, any excessive moisture?

Definitely check the head gaskets, it sounds like you could have a blown gasket, better check now while it's a 'minor' issue.

Thanks for the reply. Seems to be a bit excess water vapor while running on a cold day.

How should a head gasket job be? Is it normal to replace all of them and timing belt/ seals etc at the same time?

I agree with the blown head gasket. Had the very same thing happen on my Legacy. I never checked the miles but 12 sounds about right. No water ever showed in the oil. Had the head gasket replaced and the car's been running fine ever since.

Thanks for replying. Yeah, I have no water in the oil or oil in the coolant either. As noted above there does seem to be just a bit too much condesation/vapor on a cold day though.

How much was the head gasket job? Is it normal to replace all of them and timing belt/ seals etc at the same time?

I can't remember the exact cost but if memory serves me right,which a lot of times it doesn't, it was in the $400 range. But it was done at a dealer so other sources might be cheaper. I don't recall, exactly, if the other things were done but I don't believe they were because I didn't drive the car long enough to fry them. I almost forgot. I had the same excessive exhaust moisture when I blew a head gasket on a Dodge I once owned.

I've done the job myself ,. Check out this page :
http://home.comcast.net/~skipnospam/
When changing the head gaskets , change the tbelt and tensioners , oil and water pump ( don't cost that much ) . The cost of everything : around 1500$