What could be causing my suddenly lower MPG?

I've got the 2.7L. I used to get around 22 MPG all the time, often a little better. Suddenly I'm getting 19 or so. I did get new tires, but only went from 30.4" to 30.6", and the MPG dropped sometime after that anyway, so I don't think that's it. I'm right at the 53K mile mark. Have been very faithful with oil changes and other maintenance. I haven't changed driving habits and have made no other modifications. What could be causing it?

 

Tire tread? Tire weight? PSI in new tires?

 

Size doesn't matter. The weight does.

 

Was going to ask the same. Are the new tires wider as well? A more aggressive tread pattern? Alignment been checked lately?

 

What tires did you have and what is on now? Highway tire to an AT tire can easily cost 1-2 mpg due to tread design and added weight robs more.

 

Yeah, a more aggressive tread. I went from whatever the stock tires were (can't remember now - Firestone Destination street tire of some kind) to Goodyear Wrangler Territory AT. The new tires are not quite an inch wider than the stock. Regarding alignment, that's what finally gave me the excuse to get new tires. The alignment was a bit off, the tread was down anyway and the front right was unevenly worn, so they fixed that.

I haven't been paying close attention to my PSI. However, the stock tires were filled with nitrogen, and I know there's debate about this but I swear the PSI hardly fluctuated at all, no matter what the temperature. The new tires of course don't have nitrogen and it's winter. I'll have a look at that.

 

Winter fuel sux too

 

I was also thinking this, but wasn’t sure if that’s something they do in Texas. I definitely notice the MPG hit from winter fuel here in the midwest.

All those things are going to add up (taller,wider,more aggressive) are the new tires a LT? they are usually heavier than the P tire that come on the truck. All these might add up to your decrease.

 

Add short trips to that = 15 MPG

 

If new tires are LTs, they require more PSI to support same weight as your stock SL tires. It’s counterintuitive but it’s true.

Can always check out LT tire PSI calculator:

 

My previous tank was barely above 18 with short trips. I have been on freeways more and am holding around 19.5. The number of variables in this mix is large.

 

Just an example:

I’m running 255/80/17 now, and my truck carries 300-550 pounds of constant weight depending on the season.

Stock tire PSI is 29 and my E rated 33s require 35 PSI to support same weight. Currently I’m running 37 rear and 39 front due to towing and my truck being heavier than stock.

 

Going from Michelin ltx m/s2 (before they were Defenders) to Kumho ATs cost me 1.5mpgs in my 1st gen.

 

If it happened that quickly I would think it may be a bad tank of gas. MY not be a bad idea to check your air filter either.

Just my 2 cents

 

Trying so hard not to make a “yo momma” joke…..

 

I don't see LT on them anywhere (that's new to me). And yeah, we do winter down here but not like up there. But I think it's more about the difference between summer temps and winter temps. Our winters aren't as cold as yours, but your summers aren't as hot as ours, and we had a record hot late summer down here. I would imagine the difference between summer and winter temps might wind up being about the same.

 

Hate to sound like a broken record but tires definitely make a difference. Some are softer and more sticky than others. Great for handling, braking, acceleration, grip. Bad for rolling resistance. I'm not a tire scientist for the record.

 

I always fill up at our grocery store. Maybe I'll try Costco.

 

I looked up the tires. The Goodyear weighs 37 lb, where the Firestone weighed 31 lbs. So heavier tire, and more aggressive tread = lower gas milage.

 

tire weight, winter blend fuel. simple math. Ski