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 (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

How about 594 miles with plenty to spare:

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.