Better Gas Mileage w/ lower temps

K

kimboy

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During my 25 mile commute to work in the North-East I usually set the heat at 82 and drive with the fan off.

The air is directed towards my feet, and I'm taking in fresh air...but I don't think that matters.

To my surprise, I've noticed that my mpg has gone down quite a lot. (The computer reads a whopping 18.9mpg) While I've had my car serviced recently I began to wonder why the mileage was so low.

After resetting the temp to 68 degrees and turning the fan off again my MPG went back to normal.

Can anyone explain this? What do you think the optimal temp is to gain the best mpg. What do you set your temps to when you drive?
 
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gas laws...colder temps equal more dense intake charge...more dense equals more air into the cyl. per stroke and hence you get more power as you are getting more air in there...with relativly the same amount of fuel being added.

cold temps to about freezing would be best...too cold and then the engine actually has to make heat just to warm up the air comming in to make it prime for combustion.
 
The inside temp setting should have very little affect on your gas mileage. The only time there should be any change is when the A/C compressor is engaged. So if you don't have a problem with window fogging make sure the A/C compressor is switched off. Just remember when using the defrost mode the compressor will come on no matter what.

Koz
 
I think the wintertime decrease in gas mileage is due to a longer period of fuel enrichment during warm-up and the fact that you're plowing your big ol' SUV through denser air. The second issue goes double for interstate commuters (like me). I notice a 3 MPG drop from Summer to Winter.

I'm going to have to respectfully disagree with Casper's assessment. The throttle plate and A/F ratio controls should take of the air density issues for the engine.
 
Koz said:
The inside temp setting should have very little affect on your gas mileage. The only time there should be any change is when the A/C compressor is engaged. So if you don't have a problem with window fogging make sure the A/C compressor is switched off. Just remember when using the defrost mode the compressor will come on no matter what.

Koz
Click to expand...

The compressor comes on when I push the defrost button?!?!?! I haven't noticed, then again I haven't been paying attention. Any explanation why this happens??
 
To effectively defrost the windows all systems have the a/c help remove moisture in the air.

Koz
 
Iowa4Runner said:
I think the wintertime decrease in gas mileage is due to a longer period of fuel enrichment during warm-up

This is right. Also, there are different blends of gasoline still floating around out there. The energy bill was supposed to get rid of the crazy EPA blends, but I don't know how long it takes to get rid of the ones that provide for worse mileage.

Here is the upcoming gas change that will affect all of us. MTBE is at long last going away. The question is how will it be replaced. You might recall that when MTBE was the darling of the EPA, and the gas companies said they needed a price increase to pay for it? Well, now the same gas companies say that since MTBE is going away they will have to increase gas prices to compensate.

If you burn an ethanol blend, your mileage will suffer. Higher octane, but less energy.

What ever happened to the
Click to expand...
 
I have also noticed a slight mpg decrease since the onset on colder weather, from 18+ mpg down to high 17 mpg.

Thanks for the plausible explanations.

Steve
 

I have noticed a slight decrease in fuel mileage, too. Could it have to do with the shorter days? It seems as though there are more people on the road (Christmas shopping -- Ack!) and the average speed is slower because of traffic congestion. It burns up a lot more fuel when you have to stop & start for traffic lights instead of being able to catch them all green.

For some reason, rush hour takes longer after the sun goes down (5pm to 6pm area here) than it does during the warmer months when folks drive home while it is still daylight. Perhaps some people just cannot drive after dark!
~ :bash: ~

As for the temperature, that theory might work as well. People tend to idle the car longer when warming it up, and most folks are likely to keep the car running during short errands - so as to keep the interior warm. Maybe other people drive very short distances instead of walking to the corner store. I just don't know.

I believe that cooler, denser air is good for a racing engine (the reason for above-the-hood 'grabber' air scoops on those old muscle cars), but the effect might be different on more modern vehicles. Perhaps today's computer-controlled ignitions have rendered the difference in climate moot.

During recent driving, my mileage has gone from about 18 down to 16.5 or somwhere in that vicinity. Makes me more likely to take my 4-banger Nissan Sentra to work more often than the 4Runnner.
:(

MERRY CHRISTMAS TO ALL OF YOU!!!!
 
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Good thread here... I'm glad I found it. I was curious if my rig was doing something squirrely as I've recently noticed that my 19.5 MPG in the summer as dropped to 16.8 right now.

16+ still seems a too low though.... ?!
 
After filling up at the gas station one day, I decided to do an experiment. I reset the mpg meter and went for a drive on the highway going 55-62 mph at most. Offsetting the 10% accuracy from the reported 26 mpg leaves me with an estimated 23.4 mpg.

This was all performed with my inside temp listed at 68 degrees on a warm 45 degree day.

I still think that having a warm cabin effects the cars performance, regardless of fan speed.

BTW, my .02 cents went to pay for gas.
 
Ive noticed a slight increase in gas mileage (1.5-2mpg) from summer to winter. I assumed it was from not running the ac compressor at all. I just keep my temp on automatic at 69deg. with the defrost on and the ac light off. I never have any trouble with the windows fogging up.
 
Not long... I've been resetting it about every two weeks (or evey 3-4 fillups) since I noticed it going down steadily the last month or two.
 
Check your tire pressure. this sounds crazy to me and it's very anecdotal but....my wife is always after me to check the tire pressure on her Rx 300 Lexus. I check it and it's always 30lbs. She mentioned this past month that her gas mileage was noticeably lower as stated on her computer. I first checked for a dirty air filter but it looked fine. I then grudgingly checked her tires. To my surprise they were all 28lbs. I put them back to 30-31lbs and she says the mileage is now back to what it used to be. Go figure!
 
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