I have an 05 Dakota quad cab V8 4x4 with 79000 miles on it. Up until the last 3-4 months I averaged about 16-17 mpg in the summer and around 15 in the winter. I put new, more aggressive stock size tires on it a year ago and those numbers dropped about 1mpg. This winter I am getting 12-13. I took it on a 180 mile round trip and got 14.6. Before I would get 17 to 19.5 depending weather on the same trip. Any ideas or things to look for with this drop? Thanks.

 

Well now, you say you replaced the tires with "stock size" rubber. Mine came with the bigger P265/70R16's from the factory so I'm assuming my odometer is correct from the factory. If you varied from the original factory size tires your math will be wrong if you figured the same as before, as in miles driven divided by gallons put in.

Forget what that damned computer says as I've yet to see one that is accurate. I have the same 2005 V8 4X4 and my mileage drops 3 to 4 mpg average in the winter. I get 16 in town driving on a good day during summer driving. Only had it on the highway once since I bought it and got a best of 20.4 driving 70 mph.

I wouldn't worry to much about it, but that's just me. I have 34,000 miles on my truck.

 

Yes, mine came stock with 265/70/16's too and I put general grabber AT2's on it.

I normally calculate mpg's by hand as well.

I hope it goes back up 3-4 mpg this spring but I have never had one drop this bad during the winter. It has been at least upper 30's for temp here on my last tank and it was 12mpg. No real idling, no 4x4, mostly just back and forth from work which is about 6 miles freeway and 2 miles in town.

 

I would start with checking simple things like air filter, pull the easiest to get to spark plug and check the gap/condition of the plug, clean your throttle body. All vehicles get bad millage in the winter is normal due to the winter gas and cold weather. Also if you are using your defroster a lot the A/C pump runs and sucks up the mpg. If you let your fuel tank run 1/4 the fuel pump and filter are not being cooled by the gas so the filter may be clogged, and the pump can start to fail. Since you have 70,000 miles might be time for a good tune up anyways and check the fuel injectors.

 

if you haven't done it yet do a full 60000 mile tune up: plugs, trans flush and filter, dif oil change. depending on what size tire you are running check or air i have 265/75/16 and run 34psi. another good thing to check is your air filter.

 

Another thing to check, did your state recently increase the amount of ethanol required to be mixed into the regular gasoline? Higher ethanol content will decrease your mileage, the energy density of ethanol is lower than gas.