hey, MPG question
 

As some of you all already know, I'm new to the whole MB and car deal. So i was wondering how to find your cars mpg. Thanks for any input

Ali
1981 300 SD

Fill your fuel tank. When you do, reset your tripmeter on the dash. The next time you put fuel in your tank pay attention to how much you fuel you put in. Then record the mileage on your tripmeter.

Example:
10 gallons to refill tank
200 miles on tripmeter

200 divided by 10= 20 mpg

For most accurate and consistant results, fill all the way to the top of the neck. You'll also go further per tank...

I was always told not to fill it after the nozzle stops on it's own.

I get about 20mpg right now. I record mileage every time I fill up. Always have.
Timing, injector pump timing, Wheel bearings and brakes are on my short list of things to check.

Danny

How else are you sure the tank was filkled up to the same level each time....diesel foams differently at times and can kick the pump off at different times.

I drive two diesel cars and always brim both of 'em. Diesel fuel doesn't expand like gas. Just wait till the foam fades -- and top off.

I live in hot SoCal and have never had problems with either one. I also religiously record my mileage, and prefer the accuracy of full fill-ups.

record fuel at each fillup and don't worry about topping up
 

If you consistently record fuel amount at each fill-up, then small variations in level at end of fillup are immaterial. ANy one fillup may vary quite a bit depending of the fillup level, is car on a slant etc. But such small variations will average out. One easy way to detect changes is to track fuel usage over the last five(or any other number) of fillups. If you see a change that is not weather related or explained by other reasons then items that affect fuel usage should be checked.

That caution is applicable to gasoline vehicles that route fuel tank fumes to a canister.

I couldn't have said it better myself. I spent the better part of a day trying to explain to someone on another forum the merits of keeping a running average and they never did get it. I could never see why people were so anal about getting that last gallon in their tank, when if you just keep a running tally it is a mute point. Of course it isn't that difficult to top off the Mercedes, but to get the tank completely full on my Chevy pickup would take 15 minutes or more.

I too fill my diesel to the neck. It does not have a spring loaded overfill flap. I fill it until the pump stops automatically and then get out my flashlight and top off the tank until the foam fades and then "burp" the tank by pushing down on the bumper a few times. That seems to be quite consistent with the fuel gauge markings and it adds another 0.75 gallons to the tank too.

You've got the right of it!

A small spiral notebook (and pen) in the glove box are perfect for logging this. I don't bother carrying a calculator, but I can perform a rough reckoning in my head, and the real numbers (odometer reading and amount of fuel added) are there for future reference.

I think that routinely logging this information is a great habit to cultivate. Some folks just don't get it, though. That's fine with me until someone starts going off about how big an "improvement" some particular change made to his fuel economy... based on one tankful... figured to three places past the decimal... compared to some vague notion of what he "used to get" as opposed to real records. :eek:

Others understand perfectly well how it works. In my experience, those folks also seem less prone to realizing huge improvements due to fuel line magnets, "Tornado fuel savers", etc. :D

The little notebook is also a handy place to record date and odo readings when repair and maintenance have been performed.

On my car, I get about 3-4 gals into the tank after shutoff by jyst playing with it till I see fuel at the neck.

AFAIK, the only problems with that are for gas cars because of the evaporative canister or something to do with emmissopns.

To iron out the differences between tanks, calculate the cumulative MPG using the cumulative mileage yu have driven and the cumulative gallons you have bought. If you do not do a full refill, the incremental (for that fillup) MPG for that refill is not accurate, but in the long run the cumulative will absorb that inconsistency. Of course if you rarely fill to the top, you canot calculate MPG reliably at all.

A simple spreadsheet works well to do these numbers. You can also create a historic graph of gas prices so you can yearn for the good old days....

I would say it is easier to zero the mileage whenever you fill it to the rim with Brim (can't get that phrase out of mu mind although I never drink Brim.) Calculate the mpg and log that down. This long run is kinda difficult to do. I just make a note of what the mileage should be and if it is in that range, fine. If not, I try find out why if it does it again. For instance, if I am usually getting between 30-32 and I get 28, I start to wonder why. If not, I forget about it. Nothing to see here, folks. Just move on. Mental note. No paper and pencil or PDA.

Why bother with that? Do you yearn for the good old days where you were paid less too? Besides, that day is gone. nothing can bring it back.

How can you tell?
 

How do you tell how much fuel is already in your tank when you want to measure mpg?