10 degree C change and no MPG change?

[jayliu1984]

Can anyone with experience tell me how much does temperature affect MPG?

My car has drove through winter with virtually no change in fuel comsumption. Though the winter is mild here, so how much % will 10 degree C affect fuel comsumption?

[CigaR007]

Here's an interesting discussion on the matter.

http://ecomodder.com/forum/showthrea...cts-20561.html

[Miller88]

This week commuting to and from work, I'm averaging 37MPG ... which is pretty on par with what I usually get out of the Focus during summer commuting.

In the winter with winter blend fuel, colder temperatures and snow tires I struggle to get above 31MPG.

[MetroMPG]

Keep in mind jayliu's location: Vancouver, BC has a temperate climate: mild summers, and doesn't see very many days below freezing in the winter.

So the seasonal fuel economy variation due to ambient temperature won't be as extreme as most other places.

[Diesel_Dave]

We've had several threads on the topic. My data, as well as several others, has yeilded a rough rule of thumb: 1% FE change per 2 deg F temperature change (roughly 1% per 1 deg C).

[riva2model64]

Hm, so according to ecomodder's averages, you should be seeing a 10% change in MPG.

However, the general FE rule may still apply for you. In my area, traffic goes up when the weather is nice (when its warm out), so the higher MPG in warmer weather may be counter-acted by increased traffic.

Anyone know why FE goes up when its warm? I assume cold weather most affects the car while its warming up. A colder car takes longer to warm up and a car is least efficient when its cold (not to mention bad for the engine). Regular tires also perform worse when cold. That part makes sense to me.

However, isn't air denser when its cold? Isn't this the same effect as forced induction, jut without turbo or supercharger drag? Therefore wouldn't FE increase in cold weather, assuming the car is fully warmed-up? (By this logic, cold weather should increase FE for longer drives?)

[Diesel_Dave]

There are several effects of the cold:

1) Increased rolling resistance. Tires absorb more energy when cold, so it takes more energy to roll. Also, cold lubricants in differentials, transmissions, etc. are also more viscous which hurts FE.

2) Increased drag. Increased air density means more aero drag. A 10 deg C decrease in temp means ~4% denser air, which means 4% more drag.

3) Slower warm-up. The engine looses more heat to the ambient when cold. Also, the cold engine & transmission oil make it more viscous and cause more friction

4) Cooler, more dense intake air. This typically hurts a typical gasoline engine. The reasons are the same as why a warm air intake helps a gasser. Colder air means the throttle closes down more and pumping losses go up. Also fuel doesn't evaporate asnd mix as well, and flame speed goes down. On a diesel, cooler air typically has a slight benefit, at least to a point. Very cold air can delay the combustion and hurt FE.