Truck: 4runner '01 SR5 2wd

Info:

I had the truck BRAND NEW with only 3 miles on it, now it has around +85k and I've been averaging 19mpg until now.

I just had a major service for 85k at toyota. They did the whole deal +changed my timing belt. And I noticed that I was only getting 17mpg after the service. By the way I also cleaned the throttle body out myself (They were going to charge me +$100 for that service). Continuing on... I changed my tires from a 265/65/16or17, I forget, to the A/T Revos 265/75/16or17. I saw my gas mileage average drop dramatically. My last tank I got 14.65mpg. Somethings wrong? or the revo's really eat gas? My driving habits are good comparable to my grandma's.

 

1. You are now running a larger, heavier tire that requires more power to turn.
2. Your speedo is probably off, making your MPG calculation wrong.

Compensate for the increased diameter and it won't be as shocking, but it will still be worse than before.

 

15mpg aint bad. I have a 4popper and get around 14 to 18 depending on if I'm in the mountains or not.

 

When I changed from the P265/70-16 to P265/75-16 my CALCULATED fuel mileage dropped about 1-1.5 mpg. But I DID notice that the speedometer, which used to read about 2 mph low prior to the tire size change, is now reading dead-on at 60 mph using a calibrated radar gun. So, was I really getting better gas mileage before the tire change? If you think about it, you may be using a bit more fuel to turn the tire 1 revolution but you're also going a bit farther with each revolution with the 75's. The bottom line is that your REAL fuel mileage has probably not suffered.

Regardless, I'll bet the truck looks better with the 75's than your old tires.

 

Yes my speedo is probably off. That's a good point so my calculations probably off. But I dunno from 19mpg to 14.65mpg seems to be a big change. Is it possible that my speedo is off that much. You think it maybe that the 02 sensor should be changed already? I've been running on the same one. Would the check engine light come on if that was the case?

 

Well i went from 265/70-16 to 265/75-16 and that is a 1" difference resulring in a ~3.5% error. So if I go like 300 miles, that is about 10.5 miles I have to add on. So if I fill up 15 gallons that means I should add around 0.7 mpg to my caluculated milage.

Not a whole lot, but tire size DOES make a difference... plus they are usually better tires when upgrading (softer compound than stock rugged trails), heavier and require more to run.

Well yes your CEL would come on, but the o2 should be preventative IMO. I like to change mine every 75k. As for our trucks, I would ONLY change the rear though as its the only one that really makes a difference...

 

I always thought it was the pre-cat sensor that makes a big difference?

 

My pre-cat O2 sensor crapped the bed about 4 months ago and threw 2 codes with the CEL. I had about 94K on it when it went. Other than the CEL, I'd never had realized it. Not only was the truck running just fine, my tank-to-tank fuel mileage had actually improved slightly. Go figure...

I'll probably pick up a spare O2 sensor and wait until it craps out again rather than replace it as a PM item since it didn't cause any driveability problems.

 

It is. The rear is only there to validate that the cat is doing something.

 

I have the plus 1 size tires too and my mileage is always around 15.5-16.5 and I thought something was up since my mom's '99 Limited gets about 30 more miles per tank (over 17mpg) than mine but then I got a hold of her truck for the last two weeks and I lowered her MPGs too so it's actually my driving style which is slightly aggressive so my truck has no issues I guess.

 

Ya that is what I meant, honestly ...