Elripster,

I don't want to make you feel bad but I just filled my '79 300SD with 197k miles on it. The previous time I filled the tank was 6000+ miles ago and it consumed 217 gallons since. It averaged 28 MPG which is more than my 240D ever got. My 220D, old 190D and 300SDL get even better mileage than 28 MPG.

I don't know what is wrong with yours but you should get better than 20 MPG. I still think the IP should be calibrated and the timing adjusted.

P E H

Elripster,

I'm not an expert at ALDA adjustments since I haven't done one myself. This screw is on top of the injection pump. Folks have made the adjustment, and said they can get more horesepower because more fuel is being injected in the engine. It is possible to over fuel the engine which will result black smoke and no extra horsepower. Turning the screw the other way results in less horsepower since less fuel is being injected into the engine. I suppose the ALDA gets out of adjustment as parts wear but I don't know if that results in more fuel being injected into the engine.

Let's see if anyone else can say anything else about ALDA adjustments and fuel economy.

I adjusted my ALDA after I installed a turbo boost controller. I have the ALDA set at 1.25 full turns counterclockwise with the boost set at 14psi. Everything works well for me and there was a noticeable difference after the modifications.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

Oh I forgot, with regards to the fuel economy, I get about 23 or 24 mpg in mostly city/around town driving. Also, it's important to note that I live in an area where most of the roads are hilly.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

I've read that Chilton's diesel book. Somewhere in that book, it explains the function of the turbo--to get more power or to increase mpg.

To get more power, people increase boost pressure with an increase in fuel delivery.

I have not read about anyone trying to increase mpg with a turbo. Assuming that the turbo is not optimally set up, one could increase the boost pressure without increase fuel delivery. More air would make the fuel burn better, increasing the efficiency of the engine. I think there would come a point where addditional boost would not help because the fuel would be already burning as thoroughly as possible.

This idea would not work on a gasoline engine because a lean fuel mixture would cause the engine to stop. However, diesels run on a very lean fuel mixture.

Has anyone adjusted their turbo for maximum mpg?

This has already been mentioned in this thread, but if I had already done as many things as you have I would pull the precombustion chambers and check them and check the spray pattern of the nozzels and calibrate the injection pump. Your car only has a certain number of parts which can be replaced... I think it is down to these that could easily give you the symptoms you describe, good luck, Greg
I was getting 27 mpg on a 1981 300td turbowagon with 280,000 miles at 65+ out on the road.

Does a '79 300D have an ALDA? It's not turbocharged, so it may not have one. I don't know what MB did for altitude compensation on the late naturally aspirated diesels.

Don't forget that turbodiesels generally get better milage than non-turbos. The difference isn't huge, but accounts for perhaps 1MPG.

Also, no car back in 1979 actually achieved its fuel economy rating. The rating system was tweaked over time - always downward - so that the published numbers reflected what drivers could reasonably expect to see. The car wouldn't do 24/27 when it was new.

My 300D turbo pretty much did 23/24 in suburban commuting use. On the highway I usually got lower milage, due to high speeds and/or bicycle racks on the roof. The 123 chassis is not very aerodynamic, so fuel milage absolultely plummets with increasing speed.

My daughter routinely gets over 25 mpg, and on trips home approaches 30 mpg driving 65 to 70 mph on I90 & I91 in the 1982 240D (280,000 plus miles now). She attends RPI in Troy, New York, which is an old town on the Hudson a little North of Albany. The whole place is hills, so the tanks spent crawling around the town of Troy can get down to 20 to 22 mpg.

I would expect a 300D to do a little worse with an automatic sapping some energy, but not down to the low 20 mpg range.

I agree the car has a poor drag coefficient, and suffers when you get much above the 60 mph range, but no one ever drives that speed anymore even in a posted 55 mph zone. You would cause traffic jams, or get hit by trucks and other cars, so I have no data on what the peak mileage might be.

Anyway, the point is, I think Frank should expect at least a 15% improvement in his actual mileage. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

I'm going to start with the timing issues. The new injectors helped her run better right off the back, but I don't. think they are the big fish as far as mpg goes. They are only about 3 months old so I'll wait to test them since they are so new.

I agree that I should be at least back up to the 23-24 range the car experienced most of its life. I just need to do some more invesigation. You guys have provided me with much good info.

Frank.

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'82 300SD

Oh, about this ALDA, does this have to do with an altitude thing? Or is it a fuel mixture? Do the normally aspirated diesels have them? Mine's a non-turbo.

Frank.

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'82 300SD

Frank:

I believe you have an ALDA, but it is'nt, of course, connected to the manifold to sense boost. It is on the top side of the IP at the rear. If there is no square metal can there, is there a marked knob? The W115 300D had manual altitude compensation, set by a similar knob. Should be marked in meters or feet, from 0 to 4000 or so.

If you have an anaeroid barometer (the working part of the ALDA (= altitude compensator), it can be adjusted with the screw on top -- out for more fuel, in for less (or the reverse, I've never messed with one). Someone will know for sure.

Point is, if you are making heavy black smoke at full throttle, you need less fuel. If you don't have heavy smoke, you don't have excess fuel.

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!

I have very little smoke in this car. I can only tell if there is any an night. I would suspect the mixture is Ok, unless it's too lean.

Frank.

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'82 300SD

Frank:

You should see just a little black smoke at full throttle in 3rd gear at 45-55 mph. Only enough to just see a flicker or two above the trunk in the rearview mirror. You will see much more at night.

I suspect you are too lean, and that the injection timing is late, too, although that usually makes more smoke at high speed.

Has anyone adjusted the pump for smoke output? If so, they may have turned it down to eliminate the smoke, and since the smoke was due to late injection timing, killed the smoke but also the horespower. You will get less milage with the injection timing late.

Have the timing chain checked for stretch, or do it yourself, and if it is getting long, replace it. This will restore the injection timing, too.

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!

How much stretch is acceptable for these cars before it should be replaced? Timing chain, I mean.

ATLD

Consensus here seems to be if the cam is more than 3 degrees late, it is time to replace the timing chain. However, if the chain tensioner is still able to keep the chain tight, an off set woodruff key can be be installed in the cam drive gear to correct the late timing caused by the elongation of the timing chain.

P E H