[Diesel_Dave]

IMO, in a turbodiesel lower intake temps generally increase engine efficiency. That being said, I think there may be a point where it can go so low that it hurts. You have to keep in mind that temperature affects many things in different ways. It affects your combustion effeciency (both air temp and fuel temp). It affects your heat losses. It affects your frictional losses (both engine and drivetrain). It affects your tires and rolling resistance, and it also affects your aero (cold air is more dense). Keep in mind as well that some of those factors affect you differently depending on your trip. For example, if you have a short trip the time it takes everything to warm up (coolant, oil) is really going to hurt you. If you drive at high speeds the aero effect is going to play a bigger role, etc.

Anyway, I'm still keeping records and I'll try to update eveyone later when I have more data.