My 603 is tuned pretty well, I think it is just the way you drive. These are heavy cars with little engines they work pretty hard around town. On the highway they get moving and diesels like to run at high constant rpm's.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

My 1981 300SD gets about 22-24 around town and 26-28 highway.
HOWEVER:
My boost is upped to 12psi
ALDA is adjusted (no more too the floor to get going...just touch and go)
Fully functioning EGR (yeah right)
Decent tires
Very Little Extra Weight

Do you have additional weight in your car and/or crappy tires?
Hows your transmission doing?
Tight or slippy?
Might be due for a change of fluid and filter

I carry about 70 pounds of stuff in my trunk all the time. Then about 30 pounds in my car. So just 100 pounds on the car, not even enough weight to consider it to be an additional passenger on board. My tires are brand new (less than 2,000 miles on them) and as far as I know they're in good shape. Transmission is tight. Converted it to synthetic fluid lately. Only "defect" in tranny is a thump when downshifting into slower speeds -- normally happens when I get right off the main road which has a 50mph speed limit, into the road leading into my neighborhood with a 25mph limit. I understand this has to do with the vacuum adjustments, but for now it will just have to stay as it is till I get the time to attend to it.

I admit I have never checked my ALDA for adjustments, or my EGR. But I believe that if any of those two items were off, I would have felt their effects some other way, such as through inadequate power.

My mechanic will check my brakes for dragging tomorrow. After that if all is well, then I know I am getting what I should be getting.

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver

How do you calculate MPG???
Never trust your odometer...
Tire size has drastic effect on MPG, are yours the correct size??

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ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

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