Poor fuel mileage

My 16’ doesn’t do that. It gets up to temp (can’t render offhand what actual temperature that is) and then stays perfectly in the middle. Sounds like perhaps an overly sensitive temperature sensing unit? The truck gets up to temperature, then the thermostat opens cooling off the sensor so the needle drops, then goes back up once the coolant has warmed back up after circulating through the system.

 

The point is no matter what it has never come close to the states MPG on any road or any driving style. There are other trucks like it. Those people are probably sick of people telling them it’s their driving style or not stock or blah, blah, blah, just like I was and am again.

 

Reality is that all of those things are factors, in any vehicle, wether or not you acknowledge it.

 

What calculation do you use to correct for tire size and speedo difference when trying to come up with mpg?

 

You can use the tire calculator on here. Multiply the MPG given by your trucks computer by the percentage difference in tire size and then subtract the two. For instance, say the difference is 10% and your truck says you get 20, then in reality you would be getting 18.

 

I found that if the odometer said I traveled 100 miles and with the 265/75/16 tires on my truck I've traveled 2.5 more miles than the odometer indicates. (checked with a stand alone Garmin Zumo 595 GPS) 2.5% more miles with the larger diameter tires I have installed than the odometer indicates.

So when I fill I tank and 300 miles indicates on the odometer. 300 x .025 = 7.5 additional miles traveled.

Then take 307.5 miles divided by the number of gallons to fill the tank (say 15 gl for discussion).

307.5/15 = 20.47 mpg (this is more MPG than indicated on the display)

My testing with a GPS indicates different than what is mentioned above. I found that the speedometer readout increases with a larger tire (265/75-16) to be accurate with GPS speed but the odometer does not reflect the actual distance traveled with a larger tire diameter.

Has anyone else confirmed this with a GPS?

I'm unsure how the distance displayed on the odometer is being calculated by the truck??

 

I recall this topic coming up when I and others bought our third gens in late 2015. Once we switched tires to either 265/70/17 or 265/75/16 we noticed our speedometer was more accurate when compared to a GPS.

As long as your findings were correct you did the math correctly as well. Would have been interesting to see what the original readings were checked via GPS when you had the 265/70/16’s.

I can only assume that the odometer is read via a speed sensor on either the transmission or one of the wheels. Now why the speedometer is correct and the odometer isn’t I’m not sure. My best guess is that it wasn’t calculated/calibrated correctly from the factory, perhaps they make it display a faster speed than it is to avoid customers from speeding?

I will say that the tire calculator says your tires should be a 3.3% difference, and not the 2.5% you are getting. However it also doesn’t account for tire deflection due to the weight of the truck. The difference in 2.5 and 3.3% only equates to around .27” or right around 1/4” of deflection, seems reasonable enough to me to say that your calculations are accurate.

 

I purchased my truck in Salt Lake City and drove it back to the Midwest last fall with the same GPS and with the 265/70-16 tires, the speedometer indicated a faster speed than actual in this pic.

Speedometer was reading 2 to 3 mph fast vs GPS speed..

Here is a pic with only 111 miles on it, while driving back.

 

I get 13.9 according to the computer, but I have a manual and I drive it like an S2000...

I live in TX where gas is cheap, so will continue to drive it like it’s an S2000.

 

Got 21.2 at 70 MPH today on my commute to work

 

My general assumption/theory is that Toyota either planned to install larger 265 series tires and then abandoned the idea, hence the difference in speedometer reading. It could also be that was an easy way for Toyota to cheat the system. Allows the person driving to believe they have the cruise set on 70, but they are really getting 66-67 MPH economy. It’s not a huge difference but for a truck that already struggles with downshifting it could have been the push they needed to be able to broadcast the efficiency they claim.

 

I believe the Michelin Defenders run slightly small for their size.. I run 28 psi cold in them due to the increased load capacity over the stock 265/70-16 load capacity which could impact rolling diameter slightly also.


Both my 2000 and 2006 Tacoma's had optimistic speedometers also with OEM stock tires.

 

I will be towing a trailer tomorrow to the landfill. The trailer weighs around 2,000 lbs dry. I would estimate it has at MOST 2,000 of stuff loaded on it, so a 4,000ish pound total. Will also have a dishwasher and two washing machines in the bed of my truck. I’m not sure what my gas mileage will be when pulling it there, but if I average 12 MPG I’m going to be surprised. Will update tomorrow with the hilarious numbers.

 

Exactly. I have 30 PSI in my 285/75/17’s and if I measure top to bottom they are 33 1/2” and when measuring side to side they are 34”, so I have around 1/2” of deflection, so again I think your numbers are accurate.

 

Well i'm not going to lose sleep over it. From whats been said by the dealer its been noted on some similar tacoma's that year. Asked if getting plenty of heat once the engine fully warms up...i found no problem there. I guess they will double check it on my next service visit.

 

When mine was stock, the only way I got decent MPG was driving at a constant speed of 55MPH. If I drove on the highway and tried 70MPH it would be at best 15MPG.

 

Just got back from the dump. The weight of everything we threw away was just shy of 3,000 lbs. I would estimate perhaps three hundred of that was in the bed and the remaining weight was on the trailer (trailer itself is around 2,000 lbs).

I found essentially the same thing I did when the truck was stock, even pulling a trailer my fuel efficiency is only reduced by around 2-3 MPG. With the trailer full I was averaging 8-10 MPG, and with it empty I was averaging around 9-11 MPG. However I will say that the numbers on the way home were slightly inaccurate as I was sitting at idle for around 10-15 minutes waiting for the scales to empty. The journey home was also on a smoother road, a real highway unlike the road we took to the landfill. The entire time if I kept the speed around 60-70MPH the truck was running around 2,800 RPM, but with my tires that’s nearly what it’s normally at without a trailer.

All in all, not good, but for 34” tires and a loaded 16’ double axle trailer it wasn’t bad. I think this would also disprove the theory some have that a re-gear is required when switching to 285’s or 34’s. Might be a good idea, but if I can tow 5,000 lbs without it straining too hard, then obviously the truck can move itself just fine.

 

I've towed my 2k lb boat, and gear just fine with my bone stock tacoma...hardly know its there most of the time, except for some hills. Even pulling my aluminum 5x10 utility trailer loaded going to the dump, you have to look back to make sure its still hooked up. I don't use ECT for that one, just S5 and its fine. I still get nearly 19 mpg.

 

Mine def got better, I initially was getting 14-16 and thinking i should of just got a tundra the first 6 months but once i got up to around 10-12k miles i started to get an avg around 20 mpg. thats all mixed driving btw

 

That was my experience with my truck when it was stock also. Even with the 16’, I obviously knew it was there, accelerating and braking was different for sure, but once you were going you couldn’t tell the difference, didn’t pull the truck around or anything like that.