Odometer Accuracy on our cars.

[Rolf-Dieter ✝︎]

I just completed a zirka 640 KM round trip (398 Miles) I used a 2 year old top of the line TomTom GPS since where wanted to make sure I find my final destination north/east from Toronto, where I meet 4 other Pagoda Owners. Some photos here on Post 190 at this link ----> http://www.sl113.org/forums/index.php?topic=15847.175

I encountered 3 problems.

A) I cannot really tell when the gas tank is full or not (since I like to use the actual quantity used to calculate miles/US Gallon).

B) When I stopped for gas (engine hot) the RPM was very low and stalled the car. I was only able to engage my automatic 4th gear and drive off when revving the engine and then holding at around 200 RMP.

C) When driving at 70 MPH as read on my odometer I checked my TomTom and it showed a speed of 94 KM (where it should have read somewhere around 112 KM since 70 Miles = 112.6 KM).

My questions are if some of you can please comment ...

1) How do you accurately tell you filled your tank to full, i.e. what system do you use? I hate to spill gas and the pump does stop prematurely.

2) Have you encountered this sort of problem when RPM was too low to engage gear with engine hot (however no problem to start and go with engine cold)?

3) Could the difference in actual speed feedback between the odometer and TomTom be tire size related or is the TomTom right and the odometer needs to be calibrated?

Have any of you encountered similar problems? Love to hear your views on this. Thanks in advance.

 

[Larry & Norma]

To answer one of your questions, I have original size wheels and tyres when comparing
the speed with my Garmin the car is spot on, much more accurate than my 2005 C Class!

[Jordan]

Rolf-Dieter, it was great meeting you and getting to see your car this past weekend at Mosport.  Congratulations on your win. 

To answer some of your questions, you don't say what size tire you have on the car.  If they are not correct, that would certainly influence differences between your speedo and TomTom.  That said, my speedo is about 3% off and the tire size I believe is as original as you can get them.  When doing 100kph based on my Garmin, the speedo is reading 97kph.  My fuel gauge is also not all that accurate.  It shows full when full but the needle drops faster than the tank empties.  When the gauge shows half full I know I am still about 60% full.  The longer you own the car and with each fill up you get an idea how full the tank actually is based on where the needle sits on your gauge.  WRT filling up I can usually hear when the tank is almost full.  That is if its not too noisy.  I also don't put it on maximum (depress the handle fully) when filling up because if not sitting correctly in the tank it was froth and cause the pump to stop prematurely.  While most of the stations around where I live are full service, I always do my own fill ups.  Hope some of this helps.

[JamesL]

Not "calibrated" mine for a while but it used to be about 10% low on distance but not far off on speed!

As for fuel, I calculate a rolling average so rarely do I get a 100% accurate reading per tank.

[Rolf-Dieter ✝︎]

Thank you everyone ... your replies helped me out ... my tires are stock have not been changed as far as size is concerned.

Thanks again everyone

[Rolf-Dieter ✝︎]

Actually I'm still looking for some input from you fellows for this item "B" on my original post. Should any of you have encountered this? Might it be that the throttle linkage is binding?

B) When I stopped for gas (engine hot) the RPM was very low and stalled the car as I engaged the gear. I was only able to engage my automatic 4th gear and drive off when revving the engine and then holding at around 200+ RPM.

My question here is if some of you can please comment ...

2) Have you encountered this sort of problem when RPM was too low to engage gear with engine hot (however no problem to start and go with engine cold)?

Have any of you encountered a similar problem? Love to hear your views on this. Thanks in advance.

 

[Larry & Norma]

Doing the linkage tour in the 'technical manual' might be a good place to start.
A CO meter is also useful in setting up the IP fuel mixture.

[Rodolfo]

just a thought:

if you are not so sure that your tank is each time fully filled, you could do this:

instead of measuring over 1 time tank filling, you keep a tabel of miles or kms adding up and all the tanking you did.
In that case you will have after for instance 5 tankfillings a "floating average". It takes out the influence of one time filling accuracy.

Compare it to measuring with a clock an event of  app. 1 second: Better take 20 events and divide the time by 20. (engineering experience)

regards, Rudy

[66andBlue]

Actually I'm still looking for some input from you fellows for this item "B" on my original post. .....

You might get better responses if you would not put three unrelated questions under the same Subject header.
Why would someone who knows how to fill the gas tank even read "Odometer accuracy.." ?
Staying focused on one subject has its virtues. 

[Rolf-Dieter ✝︎]

Larry & Norma ... Thank you so much I should have researched this great Technical Manual before asking the question.

Rudy ... thanks point well taken ... only I'm a kind of perfectonist  I've taken too many assumptions in my business life, sometimes they worked other times not so well, therefore I like to be very accurate in this respect. I will use both method in future when the pump stops (record the milage and the volume) also your recommendation of say 20 fill ups and a running average. Not that it matters as far as the gas is concerned, I like to have this feedback to keep me informed how the engines health is

66and Blue .... you are right ... my bad

[hands_aus]

 B    If the car is an automatic , then check to see if the constant speed solenoid on the top of the manifold is working.