I'd have to imagine that's not a reliable workaround because it would only address an air pocket issue in/around the thermostat. If the air pocket airlocks the water pump, you aren't gonna cool the engine, for isntance.
Another issue is if the leak gets bad tenough, you can get coolant into your engine which quickly destroys your piston rings ability to seal the cylinder, and then you're into a REALLY invasive costly repair to replace rings.
Rebuilding of both heads on my car cost about $1800 at a local independent.
-- Todd H.
2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA
My 97 Legacy GT 2.5 wagon has all the symptoms of a leaking head gasket listed in this article:
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"Common symptoms: Overheating, often when slowing or stopped after extended high load driving. The overheating can be seemingly random and sporadic. Bubbles in coolant overflow reservoir, immediately after running. Sludgy residue in coolant overflow tank. Hydrocarbons in coolant overflow tank, this is tested by a mechanic with specialized equipment and is not evident visually."
According to this additional article:
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it seems that the overheating is caused by combustion gasses in the cooling system:
"When the gaskets are starting to fail, some of the combustion gasses (exhaust usually) are forced past the thin metal head gasket into the cooling system. Little by little these gasses accumulate in the cooling system and begin to create an "air pocket" if you will, inside of the engine cooling system. Depending on where this air pocket circulates to, or how large it is, it can create numerous issues. If it becomes trapped around the water pump or thermostat it can prevent coolant from flowing through the engine, which results in almost immediate overheating."
What I'm wondering is why couldn't I just stick the thermostat open somehow to keep the engine from overheating. As I understand it, the valve in the thermostat stays closed to allow the engine to warm up faster after it's started.
Apart from other reasons, an engine with a thermostat always open will run too cool. This has (at least) the following consequences:
- the engine efficiency will be reduced leading to an increase in fuel consumption.
- the humidity in the oil will not evaporate, so the oil will be degraded. This might damage the engine.
The thermostat also regulates the engine temperature. Without it the temperature would increase when the engine is working harder and decrease when not being pushed.
If your head gasket's JUST started to leak, this might keep you going another week or two, but once the gasket's "blown," the compression pressures will produce gas in the coolant far faster than the cooling system can handle, even w/ the t-stat stuck wide open.
Do you have a good mechanic or radiator shop near you? Many mechanics, and most radiator people, have exhaust gas testers that will verify what you already suspect. W/ Subie head gasket issues being well known, your analysis is probably spot on.
Best to get it fixed properly ASAP. By "properly," I'm suggesting both heads come off, get checked at a good machine shop both for warpage and possible cracks or leakage, and fixed as appropriate (reface the heads for sure!), then the block be checked for warpage (not impossible, but far less likely than head warpage, and everything reassembled w/ new gaskets. You might want to surf a bit to see if any particular aftermarket brands are recommended that you can find locally (I've seen some discussions that indicate there are some aftermarket parts that work better than OEM--I dunno.) Otherwise, OEM gaskets will work.
What you're likely to find is that regardless of the gaskets chosen, once the heads are refaced, you may never have this problem again. My machine shop buddy says aluminum heads are notorious for warping until they're "seasoned" for lack of a better term, then they can be refaced and will hold their "trueness" from then on (assuming you don't overheat the engine in the future from some other cause.)
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