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2001 Subaru Forester Overheats after Mechanic added head gasket fixer

I recently brought my car to a mechanic because I noticed my coolant was emptying from the reservoir every time I drove the vehicle. It never overheated. Took it to a mechanic to get it checked out. I was specific that I only wanted them to look into it and let me know what needs to be done. The mechanic added Bars Leak head gasket sealer without asking, told me I had a tiny head gasket leak and “it’s very minor, shouldn’t be a problem”, holding pressure, tested for external leaks and found none. I drove my car for about 30 minutes and now the thermostat , slowly, goes all the way to hot. It now does this every time I start it (I have test driven it a few times. The engine heats up to normal, and after about 15 minutes of driving it overheats). Wasn’t overheating before the “fix”, now it does. I’m taking it back first thing when they open Monday. Any possible ideas?

  1. Make sure there’s a full cooling system. 2. Don’t let it overheat - stop and sit. 3. Assess how they deal with the situation, and whether you’ll trust them for more extensive work.

This might be as simple as cleaning a clogged thermostat, but anything with cooling systems, especially on Subarus, can have bad consequences. Yours may have a head gasket leak, and on Subies there are 2 head gaskets to deal with.

I’m hoping it’s just that clogged thermostat. The coolant is full, I’ve checked it a few times. I just tried to “burp” the system for air, and the coolant level never decreased even after the engine heated up to threshold temperature. Keeping my fingers crossed. And thank you.

Either there is an air pocket in the cooling system that’s causing an overheat, the cooling fan isn’t working properly, the Bars Leaks has plugged the radiator or thermostat (not likely in my opinion), or the head gasket has become worse and is causing the overheat by allowing small amount of combustion gas into the cooling system.

Either way, it’s probably time for head gaskets, a common issue for those cars. Why your mechanic wouldn’t just offer to repair them instead of adding a chemical sealer is a good question. But if, as you say, the coolant reservoir was going low every time you drove the car, the car was broken anyway before it ever got to the mechanic.

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I was afraid of that. The reason I’m hoping that it’s the thermostat being stuck is because there was no overheating prior to my visit to the mechanic, and when I burped the radiator today, the coolant never moved, even when the car was up to normal operating temperature. Thanks for responding though. Learning all sort of fun life lessons.

Could be the thermostat, definitely worth pulling it out, if it looks even slightly warped, replace. Be sure to water-bath test whatever thermostat you decide to install to verify it opens at the correct temperature the correct opening dimension of course. Getting all the air out of the cooling system is a good idea too, inexpensive job. I expect however you need to replace the head gaskets and the relationship to the recent work is just a coincidence.

I’ll add that if my mechanic tried a “miracle fix” product without asking me if that’s what I wanted prior, I wouldn’t use them again. Whether your mechanic should have done so depends on the content & nature of your conversations about this problem. If you told them for example “I just want to get some use from this vehicle until spring” then the miracle treatment approach might make some sense.

I’ll go further than you on this, George, but you are nicer than I am. I’d knock the mechanic’s teeth down his throat. Yes, I know I have what some call anger issues ( I simply call it a bad temper). And yes, I know if I didn’t have my brass knuckles on, I’d hurt my hand.