Recently, my Mini S went from sucking 100 degree air in traffic to 75 degree air. I have noticed a marked increase in mileage. More so than any other car that I have ever driven. It makes sense to me that the oxygen content of cooler air would be greater than warmer air and maybe that explains the difference. Are their any other factors that would cause the increase in temperature to affect mileage? I.e. are the turbos effected etc. Conversely, I would guess that once the temperature drops below a certain point, mileage may begin to suffer due to cooler running temperature/thicker oil etc. I also would assume that the computerized injection/oxygen sensor system may account for temperature difference and serve to counterbalance changes in fuel economy. Any thoughts?

 

Yes, I have noticed a remarkable butt dyno appeal now that fall temperatures have taken place. Usually more butt dyno = more MPG if not used for butt dyno reasons.

Also I cleaned my engine which equalls favorable butt dyno #'s.

 

Uhhm, I have been drinking, so...only pay marginal attention to what I said before.

 

All factors remaining the same, yes your MPG would increase if the temperature dropped. Your engine's efficiency would rise with the denser air charge .

 

I'm just waiting for those cooler days. Still 95 today as we experimented with a fun-drive course...

 

Other potential factors:

My guess is that you might be running the A/C much less during 75 degree days than when it's 100 -- if so, it's a big difference maker.

The temperature affects air pressure in tires. Particularly in cold temps, lower pressures could hurt mileage.

When it gets into the early to late autumn months (depending on your local latitude) most of the fuel suppliers shift over to a winter fuel blend. Many posts in various threads have reported ~3 mpg decrease with the winter blend fuel.

 

your MPG would increase if the temperature dropped

The colder the temperatures, the worse the mpg, not the better

The EPA has added a cold cycle to the EPA mpg testing. Real life. See http://www.epa.gov/fueleconomy/420f06069.htm and http://www.usatoday.com/money/autos/...stimates_x.htm

Why worse?

• As the temperature gets colder and colder, the longer it takes for the engine to get up to normal operating temperature and economy is worse
• The colder it is, the more dense the gas. More dense the gas, the harder it is to vaporize
• Winter blends of gas get less mpg, at least from first hand observation in the East
• The colder the air, the more denser the air. Great for more HP, terrible for fuel economy. MINI is a flying brick as it is. Add more air resistance means less mpg

 

I'd say yes, to a point....

 

This one's easy! The cooler charge has a pretty dramatic effect on intercooled forced-induction engines.

1) You're getting more oxygen in the engine faster, meaning more power for lower throttle openings.
2) Forced induction engines have to retard spark to avoid detonation when it's warmer, and can run more advanced spark when it's cooler
3) You're not into "cold" weather, so the "cold weather" cycle mentioned above doesn't apply... you're talking 75 deg vs. 100 deg... not cold enough to result in delayed catalyst activation, harder tire rubber, or significantly thicker fluids (oil, trans).

...and your butt-dyno WILL notice!

My forced induction cars have REALLY come alive when it hits about 40-50 F. Just wait...

 

Yeah thats always a tough question. Traditional engines always get worse gas mileage in the cold. The turbo will get better efficiency in the cold, but usually this means more power and i wouldnt think it would overcome the engine being less efficient, but ill wait and see how my car does.