Do you get about 4 MPG less during winter ?

[07WYarisRS]

Originally Posted by TheSilkySmooth

Sorry. Almost. After warmup, With the denser mixture you require LESS throttle opening for the same torque. So now you use less throttle and you're back to zero difference AFA air temp goes ( except during cold start enrichment) It's (1) longer warmup time due to COLD ENGINE not ambient air, (2) colder oils causing parasitic drag due to energy expended in shearing the lubricants, (3) higher drag and loss driving in snow.

extended explanation: A Heated air intake at cold start would help speed engine warmup and efficiency but generally the colder and denser the inlet air the more efficient the engine AFTER warmup. Water takes a lot of energy to heat - and your fuel is being expended in heating approx 2 gal H2O additional 40-90 degrees to Op temp in the cold winter days. There goes your fuel.
1 word - Block heater;)

Yes they run more efficiently and also make more HP when temps are colder, thats why guys love running the drag strips when the temps are just perfect, cold air temps but warm track surface is PERFECT. but running more efficiantly does not mean they use less fuel.

regardless the throttle position when the pistons travel from TDC to BDC they draw in the same amount (Volume) of air. In colder weather there is MUCH more oxygen and must be compensated by adding more fuel or the mixture will be lean..
there is no way around it.
Sure there is longer warm ups in colder weather but this is why your engine idles much higer in sub zero temps then a cold start on a hot summer morning. Even at idle when the engine is warm, the engine still uses a lot more fuel when air temps are cold because of the much higher oxygen levels.

So your sayin a HOT ENGINE, I fill up, roads are completely clear but the temps are -10 I'm nopt going to see any changes in fuel economy... BS.
Engine black and water temps are normal, oils hot, tires are hot, no snow, yet a 5 strait hour treck on the highways sees far less mileage then the same trip in the summer.
And that has nothing to do with there being more oxygen in the cold air?

Why is it then older cars with carbs, ATV's motorcycles, outboards run so lean in cold weather.

[TheSilkySmooth]

Originally Posted by 07WYarisRS

... regardless the throttle position when the pistons travel from TDC to BDC they draw in the same amount (Volume) of air.

This is completely incorrect. When the engine is throttled, at a given RPM, it is operating at a vacuum and the cyl is filled with less air mass. BTW the engine does not draw in air - there is no such thing as "sucking". You are confusing displacement with air mass. AFA mileage hits in cold weather, its almost ALL coolant warmup and gear and bearing lubricant shear. In extreme cold you will see additional losses in tyre stress heat loss and oil sump Lubricant heat loss. And dont forget your heater - the energy req'd to heat the air in the cabin.

[Yaris Hilton]

Colder, denser air can burn more fuel and generate more maximum horsepower, no question. There doesn't seem to be a simple, straightforward "one size fits all" answer for the optimal intake air temperature for best cruising fuel mileage. There are many posts with data and discussion on the fuel economy fora.

[TheSilkySmooth]

Originally Posted by 07WYarisRS

. ... Even at idle when the engine is warm, the engine still uses a lot more fuel when air temps are cold because of the much higher oxygen levels.

If you have higher oxygen contenet at given throttle opening, then ECU add fuel to compensate, then you have more heat energy, then the engine idles faster, then the ecu closes the throttle some to lower RPS count. This reduces air flow and reduces fuel utilized. and you are back to stasis.