Re: Gas mileage. The thermostat housing cracked. And I always noticed I thought the temperature of the engine fluctuated way more than it should. So like anytime you have the housing off, I put a new thermostat in. What a difference! It's operates at the same temperature, it does not fluctuate. We were in a 2 hour traffic jam on the 395, near Olancha. It idled for an hour without heating up at all. In hundred degree weather. I think I'm getting at least a gallon or two more mileage. Is that possible? No other changes? Gas mileage is definitely improved.