Fuel and Engines
Oil and Oil Filters
Ford Expedition

Would the thermostat or O2 sensor cause an engine to run rich if there is fuel in the oil?

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Wiki User
August 22, 2007 6:26AM

If fuel is in the oil then you may have a head gasket or a piston sleeve is crack to rule this do a compression test and check for cracks and leaks on the outside of the car or truck.