Odometers Not Agreeing - PeachParts Mercedes-Benz Forum

Diseasel300 · #1 09-20-2017, 08:44 PM

So this pertains to a 1986 300SDL and I haven't found any info with the same symptoms I'm having.

Last year I replaced the odometer gears due to the famous crumbled gear issue and the odometer has been working normally as far as I can tell ever since. I've always noticed very poor fuel economy in this car and chalked it up to being poorly tuned, however I'm not so sure that's the full story anymore.

Recently I did several fuel economy runs with short fills in the tank. Typically 75 miles or so before refilling to see if my tuning was doing any good. I recorded anywhere from 24.5-26.5mpg over 4 fillups, telling me that the fuel consumption is relatively normal.

Now here's where it gets weird. Once the trip odometer crosses 100 miles, it becomes slow. Really slow. Normally I wouldn't have noticed this, but I've been paying attention to the fuel economy like a hawk since doing the tuning. Now I have 135 miles shown on the trip odometer, while using over 1/3 tank of fuel. The problem with this reading: There's actually closer to 180 miles done at this point according to the main odometer! The discrepancy would explain the typical poor economy I log since I tend to fill up around 1/4 tank (usually around 325 miles on the trip odometer)

To confirm the difference, I ran a trip that I know is exactly 6.8 miles. The main odometer showed I did somewhere between 6 and 7 miles. The trip odometer showed I did 3.4 miles.

What on earth? Aren't the odometers geared together? How is this even possible?! I reset the trip odometer and ran the same trip backwards and came up with 6.6 miles. That's quite a difference from 3.4 or the known 6.8!

Has this ever happened to anyone else? Is something in there loose that can be tightened up? I can understand the entire odometer system being slow or failing, but having the main odometer working and the trip odometer slowing as the miles increase is weird!