W123 coupe is about 17 US gallons, best miles out of a single tank 543 (last fill up). I travel 44 miles round trip to work and back each day using State rural highways and back roads.

results will vary.

2x on gently rocking the car side to side and allowing the foam to settle.

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All gave some, Some gave it all ~ 9-11-2001 Never Forget

People shouldn't fear their Government, The Government should fear its people.

I don't think it matters one way or the other. Does it?

You should always fill your tank when at the 1/2 point - that way, you can always save on your fuel fill bills.

I urge anyone claiming to get 32+mpg to check their odometer/speedmeter....I know I know....most craigslist adds state these cars get 50mpg on average....

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He's figured that his MPGs are 30+ because he thinks that the tank only holds 17 gallons.

I'll be willing to bet that it is actually the most common 21 gallon tank.

543/21 = 25.8

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

Some fuel filler guns are more sensitive than others too.

A few times at the station close to me I fill up and the gun automatically clicks off not even 1 second after I depress the trigger. I made sure it's in fully and the attendant wasn't looking over to shut it off (because it's "diesel going into a sedan" - it happens).

This has usually led me to think the fuel tank is full once it does the final click but when this happens you have to double check the level by looking into the neck.

But from experience I have had the chance to top off with 20.5 gallons. This was the moment the car started sputtering, right as I pulled into the station.

It's actually pretty convenient to have a 21.1 gallon tank, the estimates for the fuel gauge markings are in ~1/4 tank increments. So at 1/4 tank remaining, I could anticipate to fill up with about 15 gallons.

Those with the 17 gallon tank, you can think of it as a 16 gallon tank and each 1/4 increment of the fuel gauge is 4 gallons.

This is of course assuming that the ventilation system works (no collapsed tanks), and the fuel level indicator works.

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"and the attendant wasn't looking over to shut it off (because it's "diesel going into a sedan" - it happens)."

It sure does happen. When I first got my VW Beetle TDI in 2000, tons of people would come running up to warn me I was putting diesel in my car! I would patiently explain to them it was a diesel (and yes the motor is in front). I also made sure to tell them that I got 42 around town and 48-52 on the Interstate.

On the early VW TDI's you had to do a "Ventectomy" in order to completely fill the tank.

Ventectomy: The vent is a leftover (crossover) from the gasoline engines that require "Evaporative Emissions Systems". Since a TDI/Diesel does not utilize this system removing the "Vent" allows for the full capacity of the tank to be utilized allowing you to fit an additional 2-3 gallons into the standard tank. The ventectomy also helps to settle the foam allowing for a quicker and easier filling of the tank.

On your VW TDi unless you did the ventectomy you were never getting a true full-fill. Without removing the vent, you can defeat it by pressing the little button inside the filler neck with the fuel nozzle, you'll hear a pppsssssssss as the air escapes, allowing for more fuel to enter. After I did the ventectomy on my Jetta TDi I was able to get nearly 800 miles on a tank (but I'd get nervous around 750 and chicken out).

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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission.

Same here. If I inflated tires to near max and drove 60-65 on the Interstate I could get a little over 50 mpg. But I never went past 750 on a tank. Also, I did not have the patience back then to stay at 60. I found out the painful way how hard it was to one get my car re-primed after running out of fuel. I swore that would never happen to me again!

Oh, I never made any heroic efforts to get the 45 average I had with that car over 86,000 miles of driving. I drove 80 on the freeway on long trips, and used the AC whenever I wanted, had the tires at 32 psi all around. The ventectomy give you around 1.8 gallons more fuel...but it's true if you did this it was best to drive 40 miles or so after filling up.

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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission.

X2........AND there's no way the mpg figures cited were accurate. The cars weren't capable of returning "32 mpg" ALL the time - there's no way.

From as far back as I can remember (20 something years), my mother has been filling, and stuffing the tank in our '81 300D with no issues. I remember she would use her hip to burp the tank. Such a strange feeling in a carseat with the engine off. There was never any evidence of spills, leaks, explosions, smells, etc.

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1982 300TDT
1991 190D
2022 Metris

CJ with all due respect, i never claimed to be getting that on a normal basis i just stated my last fuel up was 17 gallons and what my trip odometer was reading, i know that my speedo is 5 mph off (60 = 55 mph), i neglected to state that my reserve light on for approx. 21 miles. my norm for a tank is around 430 to 450 miles to a tank. if anything was misconstrued that's my fault.

i too get a chuckle out of the TDi fuel economy claims with these cars.

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All gave some, Some gave it all ~ 9-11-2001 Never Forget

People shouldn't fear their Government, The Government should fear its people.

I feel like the odd one out for simply filling my tank until the hose clicks off.

What are your folks' reasons for topping off?

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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

Nah. Most people just do it that way too.

Craming it in there is a way to get consistency for mpg calculations I guess.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"