Ok, I'll admit this is a knee jerk, panic post...

I have an '06 Megacab 4wd 6spd w/ 53k miles - original owner, always totally stock.

I'm due to fill up and checked the trip odo "just because" and noticed a dramatic decrease. I typically get 450+/- miles between fill ups, today I'm down to ~1/8 of a tank (usual fill up time) and only show 36x miles. Since around 12k miles the truck has consistently averaged 15.5 mpg (hand calculated).

A month ago I changed from the original 265's to some Hankook 295's. I knew I might see a small drop in mpg's but this much?! I've checked via phone GPS and my speedo is now off by 3 mph.

I am due for a fuel filter as I change it around every 10k. I consistently buy my fuel from the same place and have never had any contamination issues.

Is there anything I should look for or check? I'm worried because I've got to take it on a 600 mi trip in a couple of weeks. Help!

 

Brother it ain't the fuel... I put on a new set of 6 Pirelli tires and my mileage dropped almost 3-4 mpg! Yep, I had a set of General Ameri-Trac's on there that had over a 100k miles on them and got great mileage but the extra friction/traction kills your ease of rolling. It'll get better but it'll take some time. Just have to grin and bear it I guess. LOL

 

Well, that's good to hear (sorry for you). I can deal with mpg loss due to the tires. I've read so much about injector failures and older truck lift pump failures I tend to be a little jumpy.

Thanks!

 

Your speedo is off by 3mph at what speed? You can use that to calculate how far off your odometer is to get a true hand-calculated mileage reading.

 

I've checked it at speeds ranging from 35-50mph and it seems consistant across the board. I haven't been on the interstate yet to check it at 70/75mph.

 

Did you take this difference in tire size into account when you figured your mileage? With the taller tires, you drove more miles than your odometer shows.

 

It's easier to check at 70 since you'll see a bigger difference. It definitely won't be consistent across the range. The faster you're driving, the more off it will be.

If you figure 3mph off at 35mph, that's 8.6%. So 360 miles on the odometer would really be 390.6.

But if you're 3mph off at 50mph, that's only 6.0%. So 360 miles would be 381.6.

 

I used my Smarty to adjust the odo not the speedo. Found a slight difference between the 2. With the odo set correctly the speedo reads 60 and your going 63ish.

 

That's the first I've heard of that situation. I thought the odo and speedo were driven from the same source. I use my Smarty to update my tire size which corrects both the odo and speedo.

 

How exactly can you change the odometer with the Smarty? Only thing adjustable on the Jr. is the tire size.