I've noticed quite a few things about my car since I've gotten it. Being an old diesel I've sorta be scrutinizing the MPG. I can take it on a state highway (99, 10, etc) halfway down the state of Washington on just a few gallons no problem. The problem comes when it's on the freeway. It eats fuels and oil as well as if it was an appetizer; I find myself putting more oil in it the more I push the engine (not surprisingly...).

Is it because it's only a 4-speed? Or is there something else I should be considering?

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- 1979 W123 240D 4-speed, 390k miles

What kind of mileage are you seeing? Have you changed all your filters, and adjusted the valves recently? Also check that your brakes aren't dragging and that the tires are filled properly.
Pushing much passed 60mph you are starting to near the top end of a 240. So you're going to be pushing the car pretty hard. Also if you've got AC and it's on that will pull your mileage down.

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My 1980 240D automatic gets around 32MPG, with AC off, and keeping it around 55-57. I got above 60, and it's the same thing. To maintain that speed, or maintain ANY speed with AC running, will pull me closer to 25MPG.

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1987 300SDL #1, 1987 300SDL #2, 1980 240D, 1982 300SD, 1994 S350, 1990 350SDL, 1991 350SD, 1985 300D, 2005 E320CDI

Gone, but not forgotten: 1981 300SD, 1982 300SD, 1987 300SDL, 1983 300TD, 1980 300CD, 1981 300SD #2, 1987 300D, 1987 300TDT, 1980 300D

Also make sure you have no leaks, which often get worse at higher engine/highway speeds.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Oil rings do not seem to scrape as well at high rpms with the 616 engine. Those engines are reving much higher in comparison to the five cylinder ones at a given speed. I suspect even when new there was a differance in oil consumption. That is between town and highway use.

Overall oil consumption is the figure you want. I would almost say increased consumption is normal at those higher rpms. Does not hurt the engine just check the oil level perhaps still more frequently when using the car on the highway. As a general rule anything more than a thousand miles per quart would be good in my opinion. In warmer weather using straight 40 diesel oil if available will reduce consumption as well signifigantly. At 305 K if true and perhaps the oil was not changed properly all the time or even normal wear is possibly present. In those cases.

To make members well aware of how much consumption of oil can be reduced with straight 40 grade post your results. I have seen oil consumption drop to about half on gas engines by doing this. You just cannot use this approach in really cold weather.

Do you have a bike rack or other appendages that increase frontal area of the car?

Sixto
87 300D^2

Most of our vehicles produce the most power per unit fuel at around 2400 rpm (also where peak torque occurs). Because of the 4 speed transmissions, their rpms are quite a bit above that at high speed. In addition, drag increases so dramatically with velocity. It is the combination of these effects that you are probably noticing. I guess a third observation may be that everything you read on CL or Ebay suggests our cars get 35-40 mpg, but reality is less for many (most?) of us.

So that begs the question, what is the low mpg that you are observing?

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

My 240D would get as high as 28 when I kept my speed down on rural roads. However, this driving situation rarely happened and if I wasn't in town I was usually doing 70+ (or slower but floored climbing a grade). 22-23 mpg was my usual under these conditions.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

These cars were built during the 55 mph law.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

my all around average is 30 mpg, that is short trips to town as well as highway Highway speeds I generally stay around 70.

thought peak torque was around 3200? forgot were I saw that.

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1977 240D turbo

I have found the sweet spot on my 240D for cruising is right at 65 MPH. If I go much higher the MPG will drop dramatically and the car feels as though its not "happy" going that fast.