I recently changed 315 75 r 17 tires to 35 x 12.5 x 17 "not much difference in height or weight, but my fuel mileage dropped drastically. I used to get around 200 miles on the odometer on a fresh tank of fuel before the tire change, however now I can only get 150 miles now. The only other change was I changed the oil from Delo to synthetic Delovac. Also now my engine temp has gone from an average of 192 degress on the edge attitude moniter to 203 degress while driving 70 mph on the highway. Can changing to a synthetic oil cause this big change in fuel mileage and engine temperatures. I currently have around 30,000 miles on the truck. Any input is appreciated.

A more aggressive tread pattern would cause this but not likely that much. The synthetic should actually improve your mileage. Maybe your just trying to light the new tires up too much:ro)

temp tells me more load on engine, how did your old tires sit on H2 rims compared to current do they stick out more, large lugs on tread. tread lugs act like dyno fitting air, could try other tires and see what it does.

temp tells me more load on engine, how did your old tires sit on H2 rims compared to current do they stick out more, large lugs on tread. tread lugs act like dyno fitting air, could try other tires and see what it does.

Ya, just go drop another grand for some different tires. Come on, he is trying not to spend all his cash. Thats why this post got started in the first place.
I think you are putting a bigger load for sure, maybe one thing you can check is your tire pressure, put it as high as recommended.

????

?

200 then 150 miles? And I thought 300 miles was weak!

I usually add 22-23 gallons after 390 miles.....

DMAX wanted in TX I was thinking the same thing ...... only 200 miles per tank???? I usually get at least 350 miles out of a tank. my best was 395.

What Should I Do To Improve Mileage?

fuel tank is 34 gallons you can go longer than when fuel light comes on. check computer i usually fill up when it gets to 31 to 32 gallons used

LarryJewel... in all honesty if you are only getting 200 miles to a tank before you did that then something else is wrong... just my opinion on that. Have you thought about taking it in for a checkup??

if my numbers are correct..with a 26 gallon tank you are getting like 7mpg and with a 34 gallon tank you are getting 5mpg...I'd say that is pretty bad. That is towing mpg and damn near a 50% drop in mileage.

Unless you drive WOT all the time then I'd take it in and get it checked.

$.02