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- - 39 MPG. A fluke? (http://www.peachparts.com/shopforum/diesel-discussion/312776-39-mpg-fluke.html)

This just hit me on the back of the head like a sledgehammer. I'm not under my car now and am going on memory, but someone help me out here...

The level of the filler neck rises to just above the level of the bumper of my W115. It therefore obviously rises above the top of the tank. The vent lines are at the top of the tank and also near or below the top of the filler neck.

On my 240, then, it would seem that when I'm filling to the top of the filler neck, at least some of that fuel could get into the vents lines.

Until recently, I had a fuel leak from those vent hoses. New rubber and clamps took care of it.

How was that fuel leaking well above the level of the tank? Now I know. I'm also adding fuel to the vent system!

This might also explain some of the "burps and gurgles" we get when we top off. That fuel has to go somewhere and, given the small diameter of the vents, takes some time to work it's way up into the system. Or not...just a thought.

Makes a difference between your W115 and a W123. your tank is flat under the car, and the 123 is verticle inside the trunk.

Charlie

Well, technicaly, the fuel tank is inside the cab, but not really. It is right behind the rearseats.:eek: Since mine is a diesel, I am not worried about a fire, diesel doesn't burn unless really compressed.

INTERESTING FACT: If you pour diesel in a pan and then throw a burning match in it, the match will go out!!

The above poster has a 74 240D which is not the same as your 83 W123. you are correct, your tank is right behind the rear seat, but there is a metal wall dividing it from the passenger compartment.

Diesel is a safer fuel than gasoline. The lighter the fuel, the easier to get it to burn, the heavier the petrolium product, the more difficult it is to get it to start burning. With gas, it is the vapors that are explosive. on the other hand, get Diesel sprayed in a fine mist, and there is a flame, it will ignite really fast.

Interesting fact:

Diesel is like a Woman, you have to work at it to create enough heat to get the fire going. then watch out, you will have a hand full.

On the other hand. Gasoline is like a Man. Doesn`t take much to ignite the fire.

Charlie

Quote:

Originally Posted by Renntag (Post 2885099)

I have added ATF, ND30, MMO and used Kerosene in most of my diesels.
I can hardly see how 1 qt of anything is going to greatly effect the math providing 39mpg.
With gently driving and ideal conditions, I do not see how it is impossible to believe. No one asked about ambient temp or relative humidity. Cool moist air would also contribute to better efficiency.

Try to duplicate the mileage you found thus substantiating your finding.

273 miles divided by 7 gallons = 39 MPG.
272 miles divided by 7.25 gallons = 37.6 MPG.

Also OP says he filled and it took just OVER 7 gallons.......I am wondering what exactly "just over" means?

If it meant .1 gallon then 273 divided by 7.35 gallons = 37.14 MPG.

Well, you know it is not a huge thing but 37.6 is less than 39.

To the OP have you checked your odo against the mile markers? What size tires you running? Undersize will make it look like you are getting better mileage than you are unless it happens to offset an inaccurate odo.