Since the winter, I've noticed that my mpg's have been going down. This past weekend I drove 350 miles (95% highway) in temps that ranged from 2 to 12 F. When I calculated my gas mileage, it was about 22.5 mpg !!! Highway driving!!!

Has anyone else observed poor gas mileage when the weather gets really cold? Or do I have another problem. (I'm due for my 10,000 mile service soon.)

 

A couple things are working against you. First, the gas in the winter is formulated a bit differently, and it seems to me makes the mileage a bit worse.

Second, on cold starts, the car will run rich longer, which uses more fuel. You also have more dense air, and a colder intake charge, which will cause the computer to use more fuel to keep the ratio correct. (technically, the car should be making more power as well!)

Lastly, double check your tire pressures. In really cold weather, you can see several PSI of pressure drop, which will also affect gas mileage.

 

ditto, real cold temps mean rich running engine, and also decrease in tyre pressure. Tyres you can fix, but the low temps are kind of tough. I would suggest only motoring south .

 

Thanks. I've been meaning to check the tire pressure but, with temps hovering in the single digits, I haven't been able to motivate myself sufficiently!

 

I have seen my MPG drop by 1-2 MPG during the cold weather

 

It's a lot of things...

You're running a bunch of accessories (lights, heater fan, defroster), the engine is running cold (thick oil) longer, the aerodynamic-brick-of-a-mini is pushing colder denser air out of the way, rolling resistance increases as tire pressure goes down, traction stinks so we spend time spinning tires or pushing snow out of the way, pushing RAIN out of the way takes energy (every raindrop you hit is a quantity of water you accelerate instantly to the speed you're going...), and the list goes on...

Also, cold dense air makes more power, especially in forced-induction cars, so we *may* be more likely to exploit that power - a heavy throttle foot (or a shivering one!) can use more gas too!

 

Seems under 20 the denser colder charge out does the befits of the colder air and the car that usally runs a little rich goes even further, very similar to how the ECU make the car go extremely rich above 4.5k but cooler air above that seems to be good at keeping the enigne running more efficent for me. Guess its all a matter of being closer to that ideal temperature.

While the other statements hold true; ECU programming seems like the omly factor that will have such an exponetial effect on MPG.

 

We just had a few nights of -40C and I can assure you as the temp goes down so does the mpg. Very normal for us northern folk. It takes almost 15 mins of driving in the dead of winter to get the engine temp to the 'normal' summer temp, so naturally it will burn more fuel.

 

Yes and it happens with more than just MINI

 

I am at 22.5 mpg as well. Down from 26 on average. The car does go like stink right now.

RR

 

Yesterday was the first time in about 2 weeks that we had temps above 20. So I braved the elements and checked my tire pressure. It was down to 29 psi. I had to go to 5 gas stations before I found one that had a working air pump!

For this last tank, I was down to 19.5 mpg! That was with about 20-25% highway driving --but temps were down in the single digits during that period of time, so my tire pressure might have been even lower.

 

I'm noticing the same drop in mpg right now, also having lots of days in a row of sub zero nights and days. I think it was 15 days in a row of nights below zero. Days haven't been a whole lot better. Yesterday the heat wave: 23 degrees! I'll check my tire pressure when my fingers defrost.

Sir M.

 

Rule of thumb is:
1psi drop per 10 degrees (F) drop
1psi drop per month due to seepage through the rubber

Personal thought: That's conservative. Slightly greater losses can be expected.