Some of you know me from the ctg N.J. 2005 I have a 84 300d turbo now with 262k miles.
We are all in the middle of the highest fuel prices ever recorded in the us. All of us diesel owners drive diesels for the fun of owning a quality auto with the best reliability bar none and of coarse in most cases, almost all diesel vehicals get better mpg than their gasoline equals. I have been on a personal qwest to get even higher mpg as I do not like supporting imported oil and the fat rich american ceo's of this country.
I would like to dwell on a finding that I noticed on both of my round trips to Denver Colorado, one trip in 2002 and the second just this past oct. 2005.
I have owned my 300d since 1997 and have always gotten 23,24 mpg around town, and 26,27 onthe high way before any work. the engine ran ok but had a bad idle. In 2000, I decided, after several attempts of different parts and settings, that my ip needed to be calibrated. Could not be calibrated because all of the delivery valves were worn at 199,000 miles. Ok, new rebuilt pump, engine runs ok, no bad miss off the highway ramp ,, problem solved.
Before 2002 trip to Denver, new rebuilt nozzels, my tips were mushroomed, and new nozzels cut down on smoke alittle. Trip to denver, no problems, I am getting my usual 26,27 mpg and sometimes almost hitting 28 mpg all while doing 70-75 mph 50% use of a/c.
Now comes the kicker. Leave Limon Co., fill up at the flying J and head to denver to stay for 4 days and leave sunday am to head back to ny. I drive in and around dever, drive up to ft. collins, back to denver, over to boulder, back to denver, over to golden back to denver. I was driving 50% city and highway. Fill up at the flying j in aurora near the airport, this cannot be right I get 30. something mpg almost 31 mpg in the high altitude of colorado and I made sure I sqeezed it in.
I was never able to duplicate this higher than usual mpg again until I went back in 2005.
I did speak to a diesel owner out in denver in 2004 at a station and told him of my findings, and he said it was the altitude and that the alda was cutting back on the fuel because of the thin air. Ok seems logical, well if the thin air of the rockies can get you better mpg, could we here at sea level trick are alda's into high altitude and cut back on air into the engine to get better mpg.
My engine ran fine out in co. with really no power loss. So is there a way to replicate this as we could not only save fuel, money and less pollution, be of only the few to realize an added benifit to owning a mb diesel.
Any suggestion guys, as I think this is a worth while subject to follow.

Peter
1984 300d 262k miles

no problem, just find a very large tank to store thin air in and you can pull it behind your car.

seriously, i dont think you can.

installing a higher gear will help some. the later cars came with a 288 gear and the gas v8s had a 247. the taller gears will compromise your takeoff from a stop but will deliver higher mpg reliably. there is debate as to how much but it if you drop the highway rpm 10% for example you will get from 5 to 10% increase in economy. some folks think it will be closer to 5 i personally have changed rear ends about 6 times and i believe you will get close to the 10% for a 10% gear change.

as they say "results may vary".

but everyone agrees it is about the cheapest way to increase economy in an already good running car.

and your numbers look pretty good btw.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

With the goals and reasons stated, I think you need to look into making your own biodiesel or converting to WVO. The other option is a 190D 2.2 with a 5 speed which seems to be reliable for 40MPG on the highway. Also, my 240D manual gives a steady 28 MPG in the city. I wish I could tell you more about the 190D but mine is still on a transport truck that is meandering through the southeast according to the handy dandy tracking function provided by the shipper.

Kevin
240D
190D

You can turn the ALDA clockwise to lower the boost enrichment, but power will drop some as well. I would imagine it would help MPG since its not enriching as much on the highway while in the turbo range.

I'm getting 23 city, 27 highway with a gallon or 2 of filtered motor oil in the tank. I see no difference in smoke / drivability at that concentration. Remember with diesel around $3 a gallon, one gallon drops my fuel price by 20-30 cents per gallon. Last tank I got the equivalent of 28 mpg city by adding roughly a gallon once my tank got down to 3/4 (i fill it to the top at the pump).

__________________
Adam Lumsden
(83) 300D
Vice-President of the MBCA International Stars Section

WVO
number of cold startups not MPG.
I am at 1700 miles w/ over 1/2 tank of petro diesel remaining.

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82 300D....went to MB heaven
90 350 SDL....excercising con rods

Peter, I don't believe that the reduction of the air density created the increase in fuel economy. The engine would reduce the available fuel, in similar fashion to adjusting the ALDA clockwise, to compensate for the reduced air density. The ALDA is hardly a precision device, so the reduction in fuel may be more than......or less than required for the reduction in air density. In any case, the ratio of fuel to air is different at the increased altitude. It might be richer or leaner than what you have at sea level.

Therefore, to duplicate such a situation would require an adjustment of the ALDA.......either richer or leaner.........the direction is unknown. You'll need to experiment and determine which direction the engine prefers. I'll take a guess and say that it should be adjusted richer (counterclockwise). Give it a try and turn the screw 1 turn counterclockwise. Then monitor the fuel economy carefully over several tanks and report back with results.

Make sure you have some good baseline data before turning that screw.

Just as a reference, the SD just got 31.1 mpg in mixed driving (10/90). The ALDA is richer, the diff is a 2.88, the a/c is off, the tires are at 34 psi, and the speed is kept between 65 and 68 on the highway. I also use 8 oz. of Power Service to approx. 13 gallons of fuel. I don't expect the SD to duplicate this result, but, I'm fairly confident of repeating 30 mpg. I got 29.5 on the prior tank.

Brian,
Wouldn’t a turbocharger negate any difference in air density?
Here at 5000ft, my ‘83TD (4 speed conversion) runs about 27mpg beating around town and better than 30mpg on the highway to San Antonio if I can stay under 80mph.
Jacob

i just averaged 25 mpg city/highway combined.. not bad for a 21 year old car. my rear end is clunking a lil when i switch it to R.. i think when i decide to change it out ill look for one of those rear ends that gives a 5-10% increase in economy.. what chasis and model is it off.. is it the W126 420SEL is it?


i averaged 27 mpg with a quart of Power Service dumped into a tank of 8 gallons.. ( my tank is collapsed slightly so i mark with a sliver of tape where the tank is at before i fill up at the tank to do calculations.. not that exact but i trust it.. 8 gallons will last me 2 weeks)

A turbo could negate any difference in air density, however, the turbo doesn't know that you are now at 5000 feet with an atmospheric pressure of 12 psi. It reaches it's maximum boost of 13 psi and you get a total absolute pressure in the manifold of 25 psi. Compare this to sea level where you get a total absolute pressure of 27.7 psi. The difference, 10%, is much less than a n/a engine would suffer.

If you wanted to have the exact same power at 5,000 feet, you'd need to crank up the wastegate to provide 15.7 psi. If the ALDA could provide sufficient fuel, and this is doubtful, the vehicle would perform exactly the same as it would at sea level. But, it would not be adviseable to return to sea level with the boost set at 15.7 psi.

Hey folks,
What I am trying to find out is why the big increase at a mile high. What factors contibute to the gain in fuel econmy with no real power loss and the engine ran some what more quite. I would expect a steady 26 or 27mpg city in the higher elevation and over 30mpg on the highway.
Any thoughts.
Peter

1984 300d 262mi. with a 307 rear

The big increase in mpg is due to lower wind resistance of the body through the air!

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1983 240D automatic, Orient Red, 174K
1983 240D manual, Biscayne Blue, sold at 341K

exactly what i was thinking.

i noticed less fuel economy running across the southern end of louisiana from texas, due i believe, to more air resistance from the heavy moist and sea level air. when i had that 80 datsun 1300 five speed wagon that was so underpowered it would only do 65 flat out, down there it would only do 60 unless driving in a large group of cars.

if what brian is saying is true, and i have no base info to say it is or isn't, this is an explanation. i have noted that the guys living around denver always report higher fuel economy, by maybe 10%.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

That sounds right to me. I suspect his ALDA is better "tuned" to 5000 feet than sea level. If you optimized the adjustment for your location you should be able to get similar results. I've never noted a difference between sea level and 5000 feet, but I don't keep careful track of my mileage, and there are always other variables. I doubt there is a significance difference in wind resistance, there isn't that muck difference in air density at 5000 feet.

I managed to get about 29.7 mpg's out of my car when I drove 155 miles at 60 or less mph's (steady speed/cruise control) My dad has hit 30.4mpg's doing the same. At 80mph I get about 23.7mpg. Its all in the speed and how long you want to take to get somewhere. Personally I'll take the extra speed/less mpg's, I'd go nuts if I kept it under 60 all the time. Thats essentially the key though, go slower and you'll get some real good mileage results.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

The only REAL way to increase you MPG is to switch from lead to iron in your right foot.

Seriously, take it easy on the throttle and your fuel tank will keep itself full longer. I've been in Denver for the least two years and I average 21mpg. That's because I'm always romping around town or doing 80mph down the highway. If I could get myself to shift at 2000rpm insted of 3000rpm and keep to the 55mph limit, I'm sure I could bump up that number to at least 25mpg.