grometsc said:
actually your logic is backwards on the air....Being the air is less dense when warm, your engine is taking in less air, and thus needs LESS fuel to combust said air. As you mentioned due to the fluids being hotter as well engine/tranny oils, they have less friction on them. The tires are running hotter, and have less roll resistance in summer months compared to winter months.
If you need less air and fuel then you just open the throttle body less, so you get less, so it just takes less pedal with denser air. Fuel combusts, and needs the O2/air to do that, so the more work your engine has to do the more you open the throttle, to make air entry easier. All I said though was performance, and I meant better throttle response with denser colder air. Also, less throttle opening means you can maintain higher vacuum levels with the same amount of O2, and all other factors the same can achieve better fuel economy with more dense air.
A big factor though is that the hotter an engine can run the greater efficiency it can achieve. Lets say at 180F the engine makes use of 30% of the available energy in the fuel, but at 210F it may reach 33% efficiency. We limit the temperature to the limits of the materials, and sometimes even lower for long term reliability. Also, the higher the Tstat, the less work the water pump has to do and take energy from the engine to reject heat.
Hotter tires also stick to the road better, so increase resistance, thats why racers will light up their track slicks and may zig zag when behind the pace car. Now because the air expands when hot, the tire pressure can be better maintained to help your rolling resistance. Or use nitrogen to prevent as large of swings in pressure from cold to hot.
