KosherBenz

Ive noticed that you get bad mpg until the car warms up. No brainer, But it seems like even when its cold out (like 30's or colder)I am not getting the best mileage. Anyone else notice this?

sosh

This is true with all gasoline powered cars. Why have you just noticed it now with an MB.

lkchris

Of course, his is a diesel and the reason is different.

sosh

Diesels are even more prone to reduced mileage when cold. I had a pair of Detroit diesels in my boat. In the summer at 2400 RPM they burned 34 Gal per hour, in the cold (below 40 degrees F) they both burned 39 GPH at the same RPM and the same boat speed. They also smoked a lot until they warmed up to 170 degrees but with the colder ambient temp the fuel consumption stayed at the higher figure.

Hattaresguy

Winter fuel, when they switch to winter fuel at the pumps you should notice about a 10% drop in mileage. No worries come April or so you will notice it going back up.

This applies only to diesels of course.

khaug

Actually, the same thing, more or less, happens to gasoline. In cold weather, refineries adjust a gasoline parameter called Reid Vapor Pressure to facilitate starting and running. This costs a small increment of fuel efficiency, although not nearly as much as the drop with "winter" diesel fuel.

Winter diesel fuel contains a higher percentage of lighter distillates which have a lower energy content per unit volume. This change in blending is done to lower the gel point of the fuel so it'll still flow at winter temperatures.

Fastbuck

It takes my CDI about 11 miles to get to full operating temp when its below freezing.