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      12-19-2016, 05:07 PM   #1
spuntyb
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Overall mileage dropped on very cold start

Last Thursday here in N jersey, I had a long shift and parked my car around 6:30am and went out to drive home around 9:30pm. I was at a satellite building that doesn't have garage parking, just an open lot. It was a cold snap that day and it felt near 0. When I parked the car, my overall mileage (which shows up on the dash in the extended display), was 21.8. When I got in the car, it turned over easily, but the engine barely wanted to idle, and the extended display showed an overall mileage of 18.0. Took about 5 minutes for the car to even blow anything but freezing air from the vents, and engine to 'wake up' and sound like an engine.

So, I lived in manhattan before this and street parked for years, including this car. Had to chisel it out of plenty of ice and snow cocoons after spending the weekend (or more) in freezing temps. Never did anything like this. I wouldn't think *too* much of the engine lagging in such cold temps, but I've parked this same car overnight in colder temps and never experienced this. The odd thing is the mileage read out.

I also know I'm running winter gas, but the mileage shouldn't change while the car is parked, and certainly not by > 5 mpg. Weird thing is, I've only been able to get it back up to 18.8 or so. I'm watching the tank closely to get an idea of actual range, but I just finished that same tank and filled up this morning so we'll see. She otherwise runs fine.

Does the mileage display changing like that seem normal? Did the sensor freeze? Is that even a thing? Not sure if there's a better subforum to post in.

Thanks for any thought!

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      12-20-2016, 02:50 PM   #2
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I'm near by in Eastern PA (near the P-Burg bridge) and my MPG dropped as well but not nearly as much as yours. I was at 26-28 before the cold and have since dropped to 23-24 overall. (mostly suburban roads, 5% HWY) How long are you letting it warm up or are you just driving from start? I find these heated seats to be nothing short of amazing as they generate lots of heat in under 2 minutes and this is just starting and going. As for the vents, it takes mine about 4-5 mins to get "going" normally if you will. I'm not used to this car as every other I've owned (as of late) has had a car starter, lol. I know why BMW doesn't offer it but damn the NE man.
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      12-20-2016, 03:37 PM   #3
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Did you happen to reset your average mpg recently or have a software upgrade that would have reset it? The more recently it had been since the average mpg was reset the more easily your short term conditions will show up in the average calculation. On very cold starts I've noticed the engine usually revs up a bit to 1000-1500 for about 15s before going down to normal idle and thats going to be a bit of extra fuel consumption.
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      12-20-2016, 05:41 PM   #4
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cold starts are a waste of fuel so the MPG decrease is normal. you're not doing anything good to your car by sitting there and letting it idle. best way to warm your car up is by starting to drive it right away.
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      12-20-2016, 06:20 PM   #5
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Quote:
Originally Posted by 6IX-F10-N52 View Post
cold starts are a waste of fuel so the MPG decrease is normal. you're not doing anything good to your car by sitting there and letting it idle. best way to warm your car up is by starting to drive it right away.
I don't idle. I start the engine, wait 20-30 seconds, and drive off. If this kind of drop in mileage is normal, I must have been in an alternate universe for the past 25 years of driving. :
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      12-20-2016, 06:37 PM   #6
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The drop is only 3.8 mpg, seems normal to me in very cold weather. I wouldn't worry about it.
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      12-20-2016, 06:47 PM   #7
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Quote:
Originally Posted by tuco44 View Post
The drop is only 3.8 mpg, seems normal to me in very cold weather. I wouldn't worry about it.
Not worried. The car is fine. I expect a drop after driving the car for some time with winter gas. This was a drop in the average mileage on starting the engine though - after having driven the car 30k miles. It wouldn't even be mathematically possible to go from 21.8 to 18 that quickly.

Oh well. I was more curious what the cause might be and if it had happened to anyone else. I still think the sensor reset somehow. Again, we went from 40-50f to somewhere in the teens before the windchill all in the span of about 12 hours. I thought the car was going to die after turning the engine over - it was very odd. Also, no recent software updates that I know of, but who knows...

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      12-20-2016, 09:00 PM   #8
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Quote:
Originally Posted by spuntyb View Post
Not worried. The car is fine. I expect a drop after driving the car for some time with winter gas. This was a drop in the average mileage on starting the engine though - after having driven the car 30k miles. It wouldn't even be mathematically possible to go from 21.8 to 18 that quickly.

Oh well. I was more curious what the cause might be and if it had happened to anyone else. I still think the sensor reset somehow. Again, we went from 40-50f to somewhere in the teens before the windchill all in the span of about 12 hours. I thought the car was going to die after turning the engine over - it was very odd. Also, no recent software updates that I know of, but who knows...

my inline 6 sounds cammed during cold starts

the drop in fuel economy isnt just because of the winter blend. fuel is less likely to vaporize in cold weather, therefore making it less efficient and causing your ECU to dump extra fuel into the engine and make it run rich.
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      12-20-2016, 09:16 PM   #9
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As a single data point, I filled 89 gas last week after having run 93 continuously for the past 8-9 months, and contrary to my expectation of an mpg drop, I saw none. This is after having the car sit in the cold (avg temp ranging from high teens to mid-30s) for 3 weeks while I was away on travel. I'm also in NJ btw...
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      01-04-2017, 08:56 PM   #10
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FWIW, the mileage reading corrected itself after going through that tank of gas. It's back to about 21 now. I still suspect it was the battery, but it hasn't happened again.

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      01-06-2017, 10:48 AM   #11
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Keep in mind when driving in really cold weather, all the oil, drivetrain, etc is cold and has more drag as well. Differential oil is really thick when the weather is hot, and it close to molasses when cold.
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      01-06-2017, 04:28 PM   #12
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MPG drop in colder weather is normal
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