Seriously?! How? I get 25mpg....


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Now you begin to see why I'm not happy.........

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

At last a 240d that has rapidly dropped from the 30mpg group to the 25 mpg one. Yours may be the first poster on our site to experience this.

What you find if that indeed proves to be the case may prove important and interesting. I have no quick thoughts on possible causes. I wore my limited brain out years ago considering what might be creating this to me all too common issue.

It did bother me that one member at the time. Purchased his car new and that his never ever did any better than 25 MPG. Combustion shape and design can impact milage yet these heads are all the same. Basically a flat plate over the bore.

I also wondered if the lack of a combustion chamber shape actually was a reason these diesels do not do a little better fuel wise. Volkswagon indirect injection diesels for example had a very pronounced combustion chamber shape.

The 240ds primary engine design dates back to the late 1930s. I also was never able to come up with any approach that would boost the ones getting about thirty miles per gallon fuel milage increased.

I even sent a note to the famous rebuilder of these engines. Asking if they ever found very strong springs in the mechanical timing advance device. They did not respond. Fortunatly the actual serious failure of those devices is pretty rare.

At the same time I wondered just how tight those spring tollerances were held to in production. Stronger springs would retard the advance curve. Aging springs if a factor at all we had no indications of this .Other than knowing if this occurred the timing advance would come on quicker.

Actually it can be checked with the electronic pulse sensor firing a strobe light. . . Some 240ds seemed to have more actual power than others as well with no reasonable clear cut explanation of why.

The 240d basic engine was not discontinued in 1984. It went on to be produced in India for some of their vehicles. A small suv type comes to mind. It is rumored that improvements may have been made to it as well. Perhaps I will go look up Mercedes Benz of India.

Thanx for your thoughts Barry .

It's frustrating to say the very least .

If ever I discover the cause rest assured I'll post it .

FWIW, I'm not the only one to ever have this same complaint, I've been on this board a long time now and others have had similar issues .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

O.K., I drove the 240D home from Phoenix and ran it out of fuel just to see how many miles one tank would take me (it has a 21 gallon tank) .

It went 601 miles and returned 28 MPG's, still not good enough for me .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

What cruising speed were you doing Nate?
I seem to be pegged to 25mpg. Long highway trips I’m doing 70-75

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1981 240D 4sp manual. Ivory White.

60 ~ 70 .

It's still not getting any better, Carlos says we'll ship the IP back to the place in San Francisco everyone raves about .

Make no mistake ~ for a slushbox equipped 240 it zips right along but it did so before and got no less than 28 MPG's in town and often got 34 + going from L.A. to Vegas and back fully loaded with thw AC cranked all the way up .

We'll see, I still love the car and would like to re spray it and re do the seats .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

That with an auto... pretty good. I’m on a 4spd and still haven’t cracked 30.

__________________
1981 240D 4sp manual. Ivory White.

Quality of diesel fuel may vary from time to time. Hard to establish that is an issue or not. When checking fuel milage.

I have also thought the 240ds would do even better at reduced piston speeds. Yet just do not have the power to really enable it. The faster the piston is moving away from the combustion start reduces efficiency. This is not a really high speed design of diesel engine.

Chrysler for example kept the same basic engine design in production from the late 1930s to 1954. Mercedes to me did this with their 616 engines. Incorporating more detail changes than anything.

From the late 1930s to 1985. Staying with the flat top combustion chambers. Where Volkswagon indirect diesel engines always had shaped combustion chambers.

Also on these engines that are really not worn that bad. Some get a lot more oil past the rings at those elevated piston speeds on the highway.

Too many people today basically never check their oil levels. They take this habit over to these really old cars and that can be a serious misteak.

The early 5 cylinder naturally aspired engines are not really good on fuel milage either as far as I can tell. We own a 77 300d as well.

What has remained almost amazing to me is for cars so old. Many have never had a rebuild of the engine. Yet the engines still remain in reasonably decent condition.

I do think that if Mercedes had sold the 240ds in north America with the five speed manual transmission. They would be even more popular today.

For those Mercedes owners that do not understand how some of us 240d owners like these cars. It is hard to explain. When I drive our 1984 300d instead it is a radically different experience.

Same basic chassis but almost another car. It just to me feels like a much heavier car. I also feel that you are far more involved with the driving experience with a 240d. Some manufactures are also starting to really phase out standard transmissions totally as well.

I do not like attracting attention. Yet these cars are getting so scarce locally now. It is becoming unavoidable. Especially with the ones in really good overall cosmetic condition.

Back to fuel milage. Air temperature changed the fuel milage with the old 1.6 volkswagon diesels. I do not know if this same effect applies to these engines. You got better fuel milage on hotter days with them. It was quite noticeable.

Absolutely agreed.

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1981 240D 4sp manual. Ivory White.

Have you guys considered making a hot air intake for the 240d? Some guys on other boards did it on gasoline cars such that air was pulled in across the exhaust manifold and netted around 10-20% gains at light throttle on the highway. I imagine it might be even better with the NA diesel. A cable and flap would allow switching from cold to hot on the go.

I don't see how a hot air intake would net you anything at all on a N/A IDI diesel engine with mechanical fuel injection. If anything, it would make things WORSE. A gasoline engine meters fuel based on the incoming air charge either by aspiration through the carburetor, or by the MAP/MAF sensor calculating the incoming air charge.

A mechanically injected IDI diesel injects fuel based on RPM and rack position and that is it. Hot air charge for a given RPM will result in very poor volumetric efficiency due to the rich fuel mix and lower power output from incomplete combustion. If anything, it would make the fuel economy WORSE, not better!

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I drove mostly turbo 1.6 liter Jettas. Hotter air contains less oxygen by volume I think. So the only thing I could reason was that the hotter day temperatures where increasing burn efficiency. How exactly was unknown to me.

Many owners observed the effect as well as myself. You got a really hot day and the fuel milage increased substantially.

It was so pronounced at the time I did wonder about stealing excess heat off the exhaust system myself. Yet concluded that so much air was ingested it may have made little to no differance. Plus exhaust temperatures are probably lower than with gas engines as well.

I estimated without any proof or experimentation that it would have to produce far less volume of heat then what was needed My other thought was to also incorporate radiator heat but those cars where overdesigned in cooling capacity already. In normal use the electric fan was not really required. The normal mass of air ingested by the engine is substantial.

Plus if there was a practical way the Volkswagon engineers would have done it. A crude estimate was on a ninety plus degree day maybe a ten miles per gallon gain was seen. There may be another poster that also owned one of these engines and noticed it themselves.. It was enough that you knew it was occurring.

These were cars with no working air conditioning. Hot days were so infrequent this far north you just lived with the situation. A few of them we owned did this so it was not a fluke.

Fuel was so cheap back then in comparison. As well these engines did pretty good as they where. Higher than posted Highway speeds did seem to hurt their normal fuel millage though. That normally was about 50 mpg highway on the Canadian Imperial gallon. Possibly 43 to 45 mpg on the American gallon. Nineteen eighty six diesel jetta models with the five speed. Where perhaps the best of that generations Volkswagon ever built. Pretty reliable, parts were cheap and they where fairly easy to work on. Rust killed them years ago around here. A simple car with a very low overall parts count.

[QUOTE=barry12345;3804127]At last a 240d that has rapidly dropped from the 30mpg group to the 25 mpg one. Yours may be the first poster on our site to experience this.

What you find if that indeed proves to be the case may prove important and interesting. I have no quick thoughts on possible causes. I wore my limited brain out years ago considering what might be creating this to me all too common issue.

It did bother me that one member at the time. Purchased his car new and that his never ever did any better than 25 MPG. Combustion shape and design can impact milage yet these heads are all the same. Basically a flat plate over the bore.

I also wondered if the lack of a combustion chamber shape actually was a reason these diesels do not do a little better fuel wise. Volkswagon indirect injection diesels for example had a very pronounced combustion chamber shape.

Correction as I cannot remember because we also pulled so many heads off their gas engines. The diesels always seemed to have a substantial crack between the valves I do remember. As long as it was not too wide it caused no issues. I still have a 80 thousand mile 1.6 volkswagon diesel engine on the shelf. It has been many years but since the head is off because it broke the timing belt.

I went and looked. The head is a flat plate design. It was unusual for the belt to break so early and at that long ago time. Volkswagon did nothing after stating the warranty time was past for the guy. In fact it had slipped my mind it was still there. Until now thirty five years later perhaps.

The 240ds primary engine design dates back to the late 1930s. I also was never able to come up with any approach that would boost the ones getting about thirty miles per gallon fuel milage increased.

I even sent a note to the famous rebuilder of these engines. Asking if they ever found very strong springs in the mechanical timing advance device. They did not respond. Fortunatly the actual serious failure of those devices is pretty rare.

At the same time I wondered just how tight those spring tollerances were held to in production. Stronger springs would retard the advance curve. Aging springs if a factor at all we had no indications of this .Other than knowing if this occurred the timing advance would come on quicker. The question I actually posed. Was did they check out each centrifical timer during total engine rebuilding for spring pressures. I assumed there were springs in the unit.

Actually it can be checked with the electronic pulse sensor firing a strobe light. . . Some 240ds seemed to have more actual power than others as well with no reasonable clear cut explanation of why.

The 240d basic engine was not discontinued in 1984. It went on to be produced in India for some of their vehicles. A small suv type comes to mind. It is rumored that improvements may have been made to it as well. Perhaps I will go look up Mercedes Benz of India. I looked it up and no information at all. Probably long out of production there as well. This is an update of a previous post. Correcting some unintentional errors.

@Shern ;

Your low fuel economy is almost certain;y cause by how you run the engine .

Most seem to continuously over speed the engine when driving a 240D manual box .

This engine was recently rebuilt, including boring the cylinders, it got better fuel economy before the overhaul in spite of # 1 cylinder having barely 200# compression (the exhaust valve was "tuliping") .

It runs great, but I an not pleased with a 10MPG loss in fuel economy when the price of Diesel fuel is $4 / gallon in many places .

I agree, the 240D's drive differently, either it speaks to you or not ~ as one who likes smaller, low powered automobiles I LOVE this car beyond any reason .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better