Trying to figure out cause of intermittent/apparent overheating on a 97 Outback 2.5L 5spd with 89000 miles. Any input is greatly appreciated!

 

A few weeks ago, i started getting frequent indications of temporary engine overheating (temp gauge would go up, then go back to normal over a few tens of seconds). Noticed coolant drop only once. Dealer said cooling system was fine and told me it was a headgasket leak (they did the "sniff" test, i.e. used the emissions tester to check for hydocarbons vapor coming from the coolant). I asked them to change the thermostat, but that didn't help.

 

Another mechanic disagreed and changed the water pump and the thermostat again, saying coolant was not circulating properly (excessive temp variations at two ends of the radiator). The problem did not disappear completely but occurs a lot less frequently (only happened 4-5 times over 600 miles of driving, same thing, temp goes up then down over 10-30 seconds). It usually happens after at least 15 minutes of driving.

 

Other clues:

Fans are operating properly, there is no sign of water in the oil, and I am not losing coolant. A chemical test looking for hydrocarbons in the coolant came back negative. On a compression test, the same mechanic that said it wasn't the head gasket eventually detected a leak on the left side.

 

I am not sure what to make of all this anymore... Anybody knows how reliable the "sniff test" is? Is a chemical test on the coolant more accurate? I would prefer to be sure that I have a gasket leak before spending $1800 on new head gaskets. Could a temp sending unit failure be causing all this?

Do more checking / investigating as required, but sorry to say, this is all classic Phase I head gasket failure.

 

I first noticed bubbles coming up in my coolant expansion tank. Along with a sludge build up in there. (97 OB)

 

Are you 'pushing' the engine when it happens? Eg - highway driving, hill, towing?

 

Commuter

Not particularly. Some highway driving, but not too fast. AC was running in some cases. Usually happens after at least 15 minutes of driving.

 

Do more checking / investigating as required, but sorry to say, this is all classic Phase I head gasket failure.

 

I first noticed bubbles coming up in my coolant expansion tank. Along with a sludge build up in there. (97 OB)

 

Are you 'pushing' the engine when it happens? Eg - highway driving, hill, towing?

 

Commuter

failed to reveal head gasket failure on phase 1s until they get pretty bad.

They seem to be even able to fool the sniffer.

If it were mine I would change the gaskets and check the valves while it was apart.