The thermostat is isolated in the cooling system. It runs around 15 PSI while oil pressure runs around 60-80PSI. So it takes a heavily torqued gasket to seal out the oil from the thermostat.
The thermostat gasket is just to keep anti-freeze from leaking out of engine.
In the head and water jacket passages of the engine, are areas where the 2 fluid circuits come close to each other. If a head gasket fails near the oil circuti it tends to either leak into the anti-freeze circuit, which can over-pressurize it and you may notice extra coolant in the overflow, or in the cylinder where it will make the exhasut have a burnt oil smell. If the Anti-freeze circuit leaks it leaks down into the oil pan by way of return passages that are under residual pressure.
If anti-freeze gets in the cylinder the exhaust smells sweet like anti-freeze and is generally white.
So, I think from what you are desribing, and the reason I mention the above, is that the only way to have cross contamination is to have a crack in the engine block or to have a bad head gasket. The thermostat seal has nothing to do with sealing either fluid circuit from each other.
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Monday, October 3rd, 2011 AT 10:32 AM