Originally Posted by carnut

Just because you stabilize the temp 10 degrees higher with a different thermostat does not mean you've increased the pressure in the system. The pressure is determined by the radiator cap. The engine and oiling systems wont care if they're 10 degrees warmer. The mechanical fan clutch only works when the air flow is less over the radiator. So I wouldn't worry about it either. Running any engine hotter allows for less friction thus a slight potential mileage improvement. Removal of the fan clutch and installing an electric fan allows you to set the on temperature which means the engine will heat up quicker which MAY improve overall mileage.