I recently took a trip, all interstate and at about 80 mph, mostly, the tach registers about 3100 at that speed. I got 22.3 mpg and used a full tank of fuel at about 40 degrees. Does this seem ok? I was hoping for better mileage with the 87 300D.

Thanks.

DS
87 300D

Not sure what average for your model but my W116 300SD widebody gets average of 24mpg and thats with a lot of hills, not open flat highway, even in the city. Woud guess you SHOULD expect better than that.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

You may need to get that checked out. I drove an 87 300 D turbo that was getting 27mpg.

Through my experience with one, the '87 300D shouldn't get less than 29 mpg. Usually its 30 or better.

I recently completed a trip running my '87 300D at speeds of 80 and 90 (3500 RPM at 90 no sweat!) and one blip to 105 on the Interstate I5, I never had it up to that speed and found a long open stretch with fresh new asphalt - what a run and no cops!

I figured I got 25.2 MPG. I believe it gets better mileage at 65 MPH, significantly better than the W123 turbo diesels I drive. It uses less oil too.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Thanks for the feedback. Now where to start looking? It seems to have good power, doesn't smoke much, uses almost no oil.
Any suggestions?

DS
87 300D

First off, the speedo has to be right for mileage tests, but you would probably sense its wrong if it was out more than 5%.
Timing chain stretch or the condition of the injectors are the first things I would look at on the engine if I were suspecting poor mileage. Does it nail much when cold?

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I checked the speedo with GPS and found it off a little, so I used the GPS on the trip to keep track of the miles, it's accurate. I will have to run diesel purge or maybe have the injectors gone through. It nails a little at start up, but I don't think it's excessive. They are known to rattle for a couple of minutes in cold temps, aren't they?
It always starts within a revolution or two even when cold, so I don't think the chain has much stretch.

DS
87 300D

I don't think you necessarily have a problem. I have a notebook in which I log mpg with every fill-up. My '84 300D gets around 26-28 mpg for my regular daily drives (100 miles a day, mostly open freeway driving at 60-70 mph).

Last summer I made two trips of 2,000 miles each on open highway at average speeds of 80-85 mph with the AC on. I got 21-22 mpg. I think once you go above about 65 mpg, the mileage begins to drop off quickly.

Well, if that's the case then too bad, 'cause she just purrs along at 80+mph, seems to really hold the road at that speed. You may be right. My old Honda Accord got 38 mpg at 55-60mph. At 75-80 it was knocked down to about 31mpg.

DS
87 300D

The 123 is a lot less aerodynamic. At 80 mph, it is using a considerable amount of it's power to push away air.

When the 124 is at 80 mph, not only does it have 0.30cd aerodynamics in it's favor, but also taller(2.65 FD) gearing and an engine with a flatter torque curve(at those engine speeds).

If everything is up to snuff, and the fuel isn't poor quality, MPG should be consistently high.

Your fuel economy is way off! My 87 300D is consistant at 30 mpg and with A/C on 28.

You should check your engine timing and timing chain to see if worn and replaced if nescessary. Also, replace fuel filters, and air filter. Have all 6 injectors pop tested and spray pattern adjusted. Worn and Loud lifters will contribute to poor fuel economy as well. If you have some or all of these symtoms, you will not get very good mpgs! BB

No one mentioned the cursed Trap Oxidizer thing. If it still has one in the exhaust line get it out and your mileage score will jump.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

My 87 603/124 gets 27-28 @ 78-80 (AC off) never seems to break over 28. Gets low 20's in the city. (Checked against my GPS, my speed reads a tad over 2mph lower then actual road speed at 60mph, [215 tires,] have yet to check the Odometer, but I expect it is off by 3-5%.)

I think with some tuning as mentioned early in this post I will do a bit better, but other then needing a new head, the car runs well.

Check for worn out rear brakes -- the calipers probably need rebuilding by now anyway, but if the rotors are thin, the backing plate for the pad will hit the antirattle spring and cause the piston to stick, and that will in turn cause the brakes to drag. You will only notice this if you actually measure the 0-60 speed and it's more than 10.5 sec (ack!!!) or if the car jerks while stopping all the time.

The rears were a mess on the TE -- no one every checks rhe rear brakes on these cars because they wear so slowly.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!