Hello, We have a 1990 F250 (460 if it's helpful) and it has developed a peculiar issue: Odometer is going up without being driven. By up, I mean it has almost doubled its odo reading; and by not driven, I mean we haven't moved it in two years.

Long story: bought it in 09 with 240000 on it. Drove it for 9 mos or so and added probably another 40k. Then it stopped running and we didn't get around to fixing it until this summer (fuel line issue). really going to miss this truck, it is way too much fun to drive, but hubby really has no use for a gas guzzler and so we've decided to sell it. I glanced at the odometer in this time and almost have a heart attack - it's reading out in excess of 550k miles! Now, Mike doesn't want to roll the thing back, but who's going to believe us? I don't think I would. So the search has been on to find some rhyme or reason as to how this could happen. At least we might be able to stop it from getting worse?

Any help is much appreciated!!

 

Wow!!! Wish I could offer an explanation, but if you hang on to a few more years, I'm sure Ford might be interested in throwing you a party for a million miles.

Maybe a wiser member here will be able to help you. This has happen in the past, but was small increments on a 460. Two tenths every few days.

Have you Binged or Googled this strange occurrence for 1987-1996 Ford trucks?

 

yes, yet without any success. It's good to know that they can tick forward in small increments on their own. Do you have any idea how? I assume this happens normally when the truck is driven, due to an inaccuracy in the odometer?

 

In 1990 these trucks have a mechanical cable driven speedometer. I believe the ODO probly has a broken gear in it and it slipped one of the number dial's while moving it(vibrations).

I have seen this happen before on older vehicles. Got to love dried out plastic gears....

 

That makes perfect sense. Thank you! I guess there is no real fix to this, right?

 

Your odometer is 6 digits.
The far right digit is the least significant digit and displays tenths of a mile.
The other 5 digits display miles.

So the maximum miles that can be displayed is 99,999.9 miles.

If you say the odometer originally read 240000 that would be 24,000.0 miles

You can't tell what the true mileage is. After 99999.9 the odometer goes back to
00000.0 miles.

On a truck that old, most inspection stations will say mileage exceeds mechanical limit.
True mileage unknown.

 

Despite the humble pie I am eating right now, I have learned something. It all makes perfect sense now. Thank you sir.