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Am I a member of the blown head gasket club?

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New member here. I've got a 98 Outback (2.5l) with 90,000 miles on it. The other day it overheated out of the blue, right after about 10 miles of highway driving. Temp shot up and I ended up with some coolant in the engine compartment. My mechanic took a look for about a day and couldn't find a problem. I did a little internet browsing and found out about the infamous "blown head gasket" on the phase 1 engine. My mechanic says no, there are no external signs of a blown gasket. Here's the way I see it:


1) mysterious overheating with no apparent external cause

2) bubbles in the coolant reservoir after driving

3) exhaust smell in the coolant reservoir


The mechanic sent me home with the car and said to call if it happens again, but I don't want to kill the engine "waiting".


Any thoughts?

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There will be no external evidence of a head gasket leak in the Subaru 2.5L DOHC engine. It is an internal leak from the combustion chamber to the cooling system. The leak will not be detectable with a compression test. If the leak is small, it may not be detectable with a hydrocarbon test on the coolant.


Cheap thing to try first: replace you radiator cap. When old, they no longer hold pressure. Hopefully your mechanic checked that.


Keep an eye on the coolant overflow bottle. Look for bubbling in it, especially after a drive on the highway (car idling, or shortly after shutdown while still hot).


Watch the level in the coolant overflow carfully. It should rise when hot and go back down as the engine cools. If it is not sucking coolant back into the radiator, it is a sign of the dreaded head gasket problem. Gasses displace the coolant, and when it cools, there is not enough vacuum to suck coolant back in.


My headgasket leak wasn't too bad. I drove for a few months with a known leak (bubbles, exhaust smell and blank gunk in the overflow). I checked the coolant level every few days and after every highway drive (after cooldown). When the overflow level rose high enough, I used a turkey baster to move coolant back to the radiator. I kept a jug of 50/50 antifreeze/distilled water in the car and added coolant as needed. Because I kept close watch on it, and my leak was small, it never overheated.


Be aware that overheating the engine (any modern engine) can damage it badly, so watch that temp gauge!

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