01 Tundra sudden mpg decrease

Hey guys I’m new to this forum here. I just wanted to see if anyone would have an explanation for my truck. So when I’m driving around town I can average about 15-16 mpg but when I get on the highway last I checked I only averaged 13 that’s at 75 turning 2500 rpm no wind no hills just flat straight road. I used to be able to get 21.5mpg all day long at 75 mph with my old tires but now I have all terrains but I don’t think a different tread pattern would mess with it that much. I’m truly stumped on this no check engine light or anything either. Thanks

 

WELCOME

 

Thank you!

 

Did you change the size when you got the at’s? Also, which tires did you have before and what at’s did you get?

 

Welcome aboard from AZ!
A change in tires can impact more than tread differences. Did you get different load rated tires? If so, what is the weight difference per tire? Rims still the same?

 

I stuck with the same size tire a 265/70r16 and still running the stock rims. honestly I don’t remember what the last tires were they were on the truck when I bought it some kinda highway terrains is all I know. Now I have Nitto Terra grapplers. The absolute best I’ve seen with the old tires was 24.5 mpg at 75 mph and now the absolute best I’ve seen lately with these new tires is just under 15 at 75 mph so I lost almost 10 mpg. To me that just doesn’t seem right.

 

Terra grapplers are definitely heavier than any highway tire, especially if you got the LT tire. The added weight would hurt your city mpg’s more than highway. An almost 10 mpg difference is substantial. You might have a warped rotor or two that is creating drag. I would check if the rotor is rubbing on the pads.

 

Thank you I did the brakes not too long ago. maybe 12k miles ago but I will check on that. actually for what I get in the city it’s about the same as they were before.

 

Terra grapplers are heavy. When I went to General AT2 LT tire I'm getting 11-12 at 75. But, they're way over sized and it makes the speedo off. I'm going 75 by the speedo but in reality and every GPS speedo I've used says I'm going 80. So, I slow down, LOL!!!

 

I've had my 2001 since new, currently at 87k miles, and I get about 18 mpg on the open road @ 65 mph and 15-16 mpg in town. 13 mpg is too low on the highway i think. I never have seen 21 plus mpg on my truck. How many miles? Proper maintenance? Chunk.

 

I'd be looking at O2 sensors and doing plugs, air filter, pcv, and cleaning the MAF.

 

This is about what I’m getting as far as MPG’s (16/18) even with 285/75/r16’s LTX Michelins. My mechanic said a bad o2 sensor will decrease mpg by 1 mile. Also, who knows what your maintenance looks like? Spark plugs, MAF clean, throttle body clean, air filter, wrong oil viscosity etc? Try unplugging your battery for a reset and do a fresh gas fill up with some STP gold label fuel additive to start cleaning your fuel injectors (easy beginning). Then tick all the other boxes everyone else mentioned above.

 

I don't think my 03 would ever get 24.5mpg. Even going down hill with the wind.

 

Thanks for the replies everyone. the truck has just under 218,000 miles on it she runs like new I did the spark plugs about 5k miles ago. I change the oil every 5k miles too with the recommended oil every time as for the Air filter, it looks good I haven’t looked into the maf or throttle body yet I’m hoping I can get around to that sometime soon and as for the o2 sennsors wouldn’t the check engine light come on?

 

Haha I was in disbelief when I saw 24.5 at first too. I have heard of a few guys getting around the same but not too often. Everyone I tell seems to be amazed that a 17 year old v8 pickup truck could do that.

 

O2 sensors won't necessarily throw a light. They can get slow to respond but still be within an "acceptable" range. Basically keeping it running rich enough to burn through fuel but still within what might be normal for a cold start.

 

Any luck on solving the mileage issue?

 

Basically it seems like at 65 mph the fuel burn isn’t bad I’d even say it’s pretty good but anything above 65 and it’s burning way more gas than it used to. I did get to rev it out for the first time in a while and that did seem to help a little but not enough to solve the problem

 

Do you have one of the bluetooth OBDII interfaces? It would be interesting to see what your Long Term Fuel Trim (LTFT) and Short Term Fuel Trim (STFT) numbers are per bank of cylinders. That fuel is going somewhere... and I'd start with a peek at the fuel trim numbers.

 

The rpm tells the story if you in the sixed gear you should run it under 2000rpm 2500 way too high rpm.Make sure you in the sixed gear.Also if you haven't replaced your differential oil at about and every 30000 miles.your mpg will drops.

 

The truck is a first gen with the 4 speed and the 3.92 rear end 2500 at that speed is normal. The engine is back to normal fuel consumption though the injectors were a little clogged. I should change the differential fluid though hopefully get it up even higher.

 

Did you remove and have your injectors cleaned?

 

Never seen higher than 18mpg in my 06 with 265/70r16 Goodyear Wrangler ATs

 

Thats the same here highway driving with the 02’ on 285/75/r16.

City is more like 10-12 mpg.

 

Good to know. That's what size I plan to do after I lift it. Not sure if I want ATs or MTs yet.

Bow that I think about it I've yet to go more than 30nmiles or so at a time in my truck since I bought it a about 5 weeks ago

 

Tread and rolling resistance of tires can make a tremendous difference in MPG. If you research many of the tire companies different options of tires within each brand, then you it will make sense.

Sounds like you recently changed to all terrains? And now have worse mileage?