Summer time my 83 300D does 30 mpg in my 44 mile trip to work confirmed with gps. In the winter I get 26 mpg

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1977 300D Lost coolant while someone else was driving
1983 300D Can't run without oil
1985 300SD (gone but not forgotten)
1990 300TE 4matic Sold
1991 Yamaha Venture
1975 Kawsaki 250 triple
1974 Honda 200CL
1951 8N Ford
2008 Wildfire 650C

I can't help re: 300D fuel economy, but I wonder if perhaps tire pressure is more of a factor in winter than the diesel blend?

Given that you lose a few psi due to contraction in colder temps, I'm inclined to think this will play a pretty significant role in lowering winter mpg figures.

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1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

Good point.

I bump up my tire pressures when the cold weather sets in. I see a lot of other cars running on tires with low pressure (sidewall collapsed in varying stages) driving around when it gets cold out.

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

OEM spec from MB is 33 MPG highway per MB documentation openly available.

No ethanol imposed on diesel, so no mileage loss besides out of spec, 30yo stuff.

Whether anyone ever got that is another story.

But I have gotten well over 500 miles in a tank in a w123, but not 600.

Ill bet economic point on this kind of a body style is 35-55 MPH.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

How about 594 miles with plenty to spare:

OK update. 600 is not possible.
After. 6 months of driving only in the city.
I got the best ever MPG. Was 528 miles. Car was filles to the brim. Iam a grandpaw LOL. I run out of fuel .and coasted into the gas station. It took the whole 21.5 gals.
That's only 24.55 MPG and my AC was not working at all leaking compressor.

On avg I get 24.5 everytime. That's in the city even with the Ac fixed.?
I drive with a 2 gallons of fuel in the trunk.I have run it down to emtpy a number of times. On avg.456 miles everytime.

This is in the city.
I never took it on a road trip all interstate yet.
Should I get more MPG on the highway? Or less due to increased rpms for extended time?

Thanks for all the input its.treaty appreciated.

Mine could probably hit 600 with cruise set at 55 and no A/C during moderate spring/fall temperatures. I've got to about 550 before but I've never kept it an honest 55 for the whole tank.

Right now with 50% A/C use my reserve light comes on at about 460-480 miles. In the winter it comes on closer to 400-420 miles. This is with mixed driving.

There is no way to get 600 miles to a tank under normal conditions. You would have to try really hard under the right conditions.

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1984 300 SD 384,000 Miles

you'll get at least 2 mpg more on the highway, at least. I found the AC costs about 2 mpg when running.

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1983 300D, the "Avocado"
1976 240D, 4-spd the "Pumpkin", SOLD to Pierre
1984 190D, 2.2L, 5-spd, my intro to MBZ diesels, crashed into in 2002

Ive gotten >500 in my 83 300D on long trips. Im not sure 600 is doable, but better than you are getting is...

Id make sure youre running a 90wt diff oil and dex VI or a lower viscosity ATF of youre really trying...

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Impressive. Is this with a 2.88 or 3.07 diff?

Back in '85 I had a 'fresh' '83 SD that routinely did 32mpg. The current '85 does maybe 30 mpg and the '84 with the 3.07 does around 27 mpg. Tired vehicles and fuel changes most likely...

BTW, does your SD always run that hot?

That's about where my SD sits for temps. It is routinely over 100F out right now.

I have been getting about 17-20MPG lately driving mixed city and highway. I have a new set of Monarks installed as well. I also mix in some cetane boost from Diesel Kleen.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

This is the 2.88.

I've done well with the Power Service and the speed limit of 62mph for most driving.

The temperature gauge, I'm quite convinced, suffers from a fluctuating sending unit. Sometimes it runs right at 90°C...........sometimes it climbs to 105°C. The infrared gun always shows a maximum of 93°C at cylinder #5.

I've got a new sending unit. Hopefully, that cures it. A new clutch fan, radiator, thermostat and relatively new water pump certainly made no difference.

17-20 mpg sucks. There's something seriously wrong.

............odometer slipping............


The SD was doing about 24 mpg for a period of six months before it finally quit. $125. later and it was back to the expected 29.

My speedometer assembly was from a gas model but I recently purchased a working speedometer assembly from a member here. I verified the speed was correct with my GPS but I'm not sure I remember verifying the mileage. The gears looked intact. The top 6-digit meter is a little off from the lower trip meter. When the 10ths place rolls around, it gets to about 1-2 tenths before the top meter clicks over. I'll check it against the GPS on the ride home.

I filled up yesterday and the odometer was at just under 250 miles and I put just under 14 gallons in to top it off. I added 1.5 gallons of UMO at 1/2 tank when I changed the oil last Friday. I was just under 20MPG without considering the UMO. With considering the UMO, I am just over 16MPG. Driving conditions this last tank were harder than usual, though.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge