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How much does outside temp alter fuel mileage?

We have been noticing our fuel mileage dropping and the only real difference is the temps we have been running in... Sometimes all the way down to -30!! Would putting a barrier up in front of the radiator (to maintain a warmer engine temp) help? Or does engine running temp make much difference?

Thanks in advance for any answers!

Update

Well I think we found the problem... We ended up getting some codes (check engine lights) and it turned out to have a problem with the DEF stuff.. Husband can explain it better... But that is ow fixed, and our fuel mileage is getting back where it should be, or at least was running before...

Thanks for all the replies!!

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Well we put some small amount of cardboard in front of the radiator to try to have the engine run warmer... Looks like almost a full 1/2 mpg difference (6.6-7.2) !! But that was only one tank of fuel, and temps only in the teens, instead of negative numbers... We will see how it goes :)

Just by this one tank though, I would guess that the outside temp DOES make a difference, if only because it cools the engine down.

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If your engine has a problem maintaining operating temperature in cold weather than a winter front will help. The warmer your motor the better the fuel burns. In cold weather your fuel mileage will drop mainly because of the winter fuel blend plus a few minor factors.

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My truck pulls just a little harder on a cold, damp day, than it does on a hot, dry day. However, I think the MPG loss you are asking about is due to the winterized diesel fuel.

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The cold affects your mileage in several ways like everyone has said so far winterized fuel cause you lose BTU's with winter fuel, then you lose mileage cause transmission & diff oil is so cold and thick. Then you have outside temp that the colder it is the closer the molecules become which in turn is going to make it much harder and require more power in order to pull the truck and trailer thru the air.

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In addition to all of the above, don't forget how much the cold effects tire pressure. My tires went from 95 psi @ 30deg. F. to 85 psi @ 10deg. F. (Checked cold.) They do warm as they roll, however the road is usually somewhere close to ambient temperature, especially at night, constantly cooling them. One good thing, is, because of the cold, your tires wear very little. I know, not much consolation.

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That is one thing we didn't think of...

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Colder the temperature the more dense the air is. Therefore making it more difficult and more resistance to go through thicker air rather than warmer air. Winterblend fuel is another factor, as well as the roads might be wet or snow packed or slushy

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Gary & Paula will be eternally grateful.
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