I drive a 94 dak with a 5spd trans and the 3.9 engine. In the summer i averaged 20mpg but now that its cold out i'm only getting around 15mpg! I dont understand how it can drop 5mpg just because of cold weather. My check engine light isn't on and it seems to drive the same as it always has. Air filter is clean, oil is good, tire pressure is fine, etc..... How can this be happening? Anyone else see big drops in mpg in the winter?

ugh... Wisconsin winters are harsh.....

 

Winter gas?
But, they should have started using winter gas at the pumps a while ago up north.

Do you find yourself idling more?
Is there a difference in your driving habits (driving more city)?

For a mix (city and highway), for an auto transmission at least, 15MPG isn't bad.

The colder temps will cause more use of fuel, yes.
It will also lead to a longer time to reach closed-loop cycle (meaning, it won't take readings from the oxygen sensors, and other inputs, into determination for a longer period of time)

 

I drive the same routes and drive the same way as I usually do. I usually only let the truck warm up for about 5mins in the morning too. Maybe its the ideling thats doing it.... but since I purchased the truck I've had some issues with my O2 sensor so maybe that has something to do with it. My check engine light comes on once in awhile when I'm driving at a consistant speed (usually around 55mph). I'm pretty sure its my O2 sensor. The weird thing is that once the light comes on if I throw the truck in nuetral and turn the truck off and on the check engine light goes away. Thats the only reason I haven't changed the sensor. Maybe its time I change it....

Any ideas?

 

i wondered about the same thing. but with the below average temps we've been getting around here i'm not surprised. my dad told me our trucks have a winter setting in pcm that adjust the motor to the colder temps and thats what could be causing the change. he's had to take his truck in for the last 2 springs because it won't go back to summer mode. don't quote me on that though. your lucky though, mine dropped significantly. i now get almost 275m to the tank.

not sure what area your in but by my work in west allis peoples cars have been getting stolen because they leave them running to warm them up. just a warning..lol

 

common issue in colder areas... you let your truck warm up longer.
my V8 went from around 15mpg to almost 11mpg

 

Haha I know west allis pretty good, its pretty crazy compared to whitewater where I live(about an hour away from west allis, and 15mins away from jainsvile).

Winter sucks.... hopefully I can bring my mpg up by not letting it idel so much

 

i actually have to be out in whitewater in a few daysbecause my insurance premium is about to expire(the agent has taken care of my family for over 15yrs). i'm glad though i work for a home remodeling company. we're putting a huge garage addition on my house and i haven't had to really drive anywhere for the last 2 weeks(except for the coolant the other day and gas). its just been up and down the driveway. but i digress, just be glad you don't have my friends truck which only gets a whopping 10mpg on the highway right now lol

 

I wouldn't let it idle so much. I've done that a few times in the winter, when it gets really cold, so I don't have to drive a truck in sub 0 degree Fahrenheit weather, waiting 10 min for it to warm up. My gas mileage will drop from 16 to 14 just from letting it idle for 5 minutes. You only need to let it idle for about 15 seconds before driving off.

 

i once let my truck idle while i was shoveling it out, and by the time i got in and tried to go to work the needle was on "e". that was the last time i let it idle for a half hour.

 

ok, so where to start... vehicles dont have a winter or summer mode set into the pcm. theres no such thing. the only thing that changes in the pcm from winter to summer is how long it stays in the open loop cycle. your mechanic is raping you for fixing nothing....

second, if you dont want your motor to burn oil, you'll wanna let it warm up for at least 10 min, and not drive it hard until its fully warmed up (ie. hard acceleration). the intake plenum was not designed properly and has a huge oil burning defect.

third, what was your gas gauge at when you started it and let it idle for 30 min shadowthedakota? couldnt have been too far off the e line to begin with. ive idled mine for an hr because i locked the keys in by accident and the gauge didnt budge. in all reality, you have about 3 and a half days before you run outta gas at idle from a full tank..