Odometer Inaccuracies Anyone? - PeachParts Mercedes-Benz Forum

gmercoleza · #1 05-23-2006, 04:32 PM

1985 380SE excellent condition - can't even tell the engine's running. Just over 121K (I think...keep reading).

Long story short. I became suspicious of my odometer as a result of very poor average calculations of 12mpg. This was for mostly city driving, accelerating V - E - R - Y slowly (economy gauge out of the red) and using cruise control almost all the time (even on 30mph roads).

I used Microsoft Streets and Trips to measure actual miles covered over the last couple of days. My odometer reported 31.8 miles but I actually travelled 46.7 miles. So the odometer appears to be reporting roughly 68 percent of actual miles travelled.

I went back and re-calculated my mileage figures (I keep a very meticulous log) and if the odometer behavior has been the same over the last month then I actually average 17 to 18 mpg in mixed driving which sounds more consistent with my 380SE experience.

I will of course closely monitor my routes and mileage for the next month to confirm my calculations. Has anyone else experienced this? Any thoughts? What causes this and can it be corrected?

t walgamuth · #2 05-23-2006, 08:18 PM

it will only get worse til it doesnt work at all.

it can be reglued. slipping odo gears are one of the most common problems. it is the vdo instrument. .. not made by mb.

tom w

Hatterasguy · #3 05-24-2006, 12:13 AM

Pretty commen part of owning an older MB. Pre 85 models seem to be extremly prone to this.

MTI · #4 05-24-2006, 01:05 AM

Not just pre-85 . . . every car (MB, Volvo, Porsche) that has the mechanical VDO odometer has the same problem with the pot metal gear and supports. There's a problem when drivers reset the trip odo when the car is in motion as well.

t walgamuth · #5 05-24-2006, 07:12 AM

it is one of the few parts on a benz that is just ordinary. so it stands our, especially on a 123 or 126 which are extremely durable in general.

tom w

gmercoleza · #6 05-24-2006, 09:34 AM

I have now driven exactly 142 miles and odometer is only reporting 93.5 which comes out to only 65.8% - looks like the "slipping" can vary randomly. Using an average of 67.2% I have retrocalculated my mileage figures. It looks like in very conservative mixed driving (i.e. slow acceleration and cruise) I am averaging 19 mpg! That's nearly as good as my 300E! And to think I thought I was getting only 12 mpg... I did some research and the 85 380SE is supposedly EPA rated at 17/21 - can anyone out there confirm this?

This also brings up a sad story. About a year ago my dad donated his restored 79 450SEL with about 120K to a local charity. At the time, he felt it was not a practical vehicle because it was only getting about 10 mpg. I wonder if his odo was also inaccurate - if so, what a shame... It was in great condition, definitely an 8 or 9 out of 10. Anyone know typical gas mileage for a W116 450?

Mismost · #7 05-24-2006, 01:18 PM

You could call Rick Borth, Overseas Speedometer, 800 444 0292. He is Austin and does great work.

www.speedometer.com

If I can't fix it with a bigger hammer, I find someone who can!

Hatterasguy · #8 05-24-2006, 09:49 PM

Quote:

Originally Posted by MTI

Not just pre-85 . . . every car (MB, Volvo, Porsche) that has the mechanical VDO odometer has the same problem with the pot metal gear and supports. There's a problem when drivers reset the trip odo when the car is in motion as well.

This is the thing I don't remember about the W126 since it has been a couple of years since I have had a guage cluster apart. The odo is wire driven off a sending unit on the trans. So where are the gears that slip? Their is no cable on the W126's yet still slippage happens.

t walgamuth · #9 05-24-2006, 10:35 PM

Quote:

Originally Posted by gmercoleza

I have now driven exactly 142 miles and odometer is only reporting 93.5 which comes out to only 65.8% - looks like the "slipping" can vary randomly. Using an average of 67.2% I have retrocalculated my mileage figures. It looks like in very conservative mixed driving (i.e. slow acceleration and cruise) I am averaging 19 mpg! That's nearly as good as my 300E! And to think I thought I was getting only 12 mpg... I did some research and the 85 380SE is supposedly EPA rated at 17/21 - can anyone out there confirm this?

This also brings up a sad story. About a year ago my dad donated his restored 79 450SEL with about 120K to a local charity. At the time, he felt it was not a practical vehicle because it was only getting about 10 mpg. I wonder if his odo was also inaccurate - if so, what a shame... It was in great condition, definitely an 8 or 9 out of 10. Anyone know typical gas mileage for a W116 450?

i dont know from experience, but i wouldnt be surprised if that is normal mileage around town.

tom w

gmercoleza · #10 05-25-2006, 08:55 AM

Quote:

Originally Posted by buckwheat

You said 68% in an earlier post, and 67.2% in a latter. That's pretty consistent.

You didn't mention speed accuracy. Is it obvious you're going 100/68, or 47% faster than everyone else? Are you watching your speedo while the car is supposedly not coming up to speed?

My guess is you put 18+" wheels and even larger OD tires on the car - when the speedo was originally calibrated for factory tires?

67.2% is what I used as an average, since I measured as high as 68% and as low as 65.8%. But I figure if the percentages can swing by 2.2% just over a couple of days, who knows what it has been doing for the last month? Speedometer is 100% accurate with my wife following me in a brand new minivan. Stock 14" bundt rims with 205/70R14 Pirellis.