Why is my '79 240D doing only 20 miles per gallon? - Page 3 - PeachParts Mercedes-Benz Forum

rino · #31 02-21-2007, 02:24 PM

Quote:

Originally Posted by LarryBible

There are ZILLIONS of variables in fuel mileage. The first one that comes to mind when reading the original post is driving conditions. If you are driving stop light to stop light in town with no highway driving, then 20 MPG might not be too far off the mark.

So, conditions as described above are probably the biggest variable coupled with driving style. The next most important consideration is vehicle weight which is fixed, but if you are hauling around a spare engine in your trunk or it is packed with tools or bootleg whiskey it will have a considerable MPG effect.

All that said, if you drive mostly highway miles with an empty trunk, you do need to pay some attention to the car. If this is the case and you are getting 20 MPG I would expect to see black smoke out your tailpipe.

Yes, it is city driving only, stop light to stop light... In the trunk there is a spare tire, a one-gallon jug of engine oil, a couple of wrench/socket sets along with a hammer and a couple of screwdrivers... I assume that can be considered an empty trunk...
No highway miles... No black smoke... BUT, I just noticed, when pushing the car in neutral there's a soft screeching sound seemingly coming out of the rear left wheel (break dragging?) If it were a break problem, could that also account for the clunking sound I've been getting lately especially when making turns?

Rino

FineOlBenz · #32 02-21-2007, 04:32 PM

Your tires at 195/65/14 are slightly taller than the 175/75/14 that the vehicle calls for by the manufacture. The 185/70 /14 is the same diameter as a 175/75/14, your only very slightly larger than that. I don't think that slight difference is going to have that large of and effect. 195/70/14 is what the 300D Turbo calls for. Your in beteen the two which is not bad. Try some of the fuel system cleaners that are out there, run the valves and check timing chain stretch. The injectors can be pulled appart for cleaning and is not costly. I don't recommend changing injector knozzels unless there is a spray pattern problem. Only after that would I consider checking injector pump timing. It also sound like this car needs to be driven, like get it out and run it. It may be comoing up to a nice weekend for a HWY1 run up the coast. I was surprised after letting my son drive mine. It actually ran better. (Thank God, I'd have bury him otherwise).

diametricalbenz · #33 02-21-2007, 04:49 PM

Rino, I met up with you and Joe a LONG time ago at the Tommy's. We're having a fun run drive (about 10 cars so far) presumably from Malaga Cove to Newcomb's Ranch up the 2 freeway Saturday morning. You're welcome to bring the 240D. The drive will definitely unclog a lot of the carbon!

rino · #34 02-21-2007, 08:46 PM

Quote:

Originally Posted by FineOlBenz

Try some of the fuel system cleaners that are out there, run the valves and check timing chain stretch. The injectors can be pulled appart for cleaning and is not costly. I don't recommend changing injector knozzels unless there is a spray pattern problem. Only after that would I consider checking injector pump timing. It also sound like this car needs to be driven, like get it out and run it. It may be comoing up to a nice weekend for a HWY1 run up the coast. I was surprised after letting my son drive mine. It actually ran better. (Thank God, I'd have bury him otherwise).

I have already gone through five Lubro Moly Diesel Purge cans (adding one to the tank when refilling fuel) with no improvement in mileage. I will soon put in a new fuel filter (but I need to steam clean the engine first - it's such a mess that it will surely screw up the procedure for changing the filter...) A long trip up the coast is certainly a good idea, but I need to first take care of the brakes, and the rumbling/clunking noises coming from the rear I've been experiencing lately... it sounds like a piece of the car is about to fall off... I am kind of concerned.
There are so many things about the car that need my prompt attention that it is almost overwhelming... I'm trying to do one step at a time. I am well aware it is only my fault... I've owned and driven this car for nearly two years and I'm starting only now to try and take care of it.
For all that maintenance work you are suggesting - I don't think I have enough experience to do it myself and obviously I need someone expert I can trust... and I have no idea whom I can bring my car to locally. I'd appreciate some suggestions from other angelenos....

Rino

rino · #35 02-21-2007, 08:52 PM

Quote:

Originally Posted by diametricalbenz

Rino, I met up with you and Joe a LONG time ago at the Tommy's. We're having a fun run drive (about 10 cars so far) presumably from Malaga Cove to Newcomb's Ranch up the 2 freeway Saturday morning. You're welcome to bring the 240D. The drive will definitely unclog a lot of the carbon!

Hi, I remember you well... I'd love to come along, but before taking a long trip I really need to check and see what is wrong with my brakes and resolve the rear rumbling/banging noises that have been going on when making turns as of lately.
Your planned trip sounds like fun! You can definitely count on me coming along in the future, after I'll have taken care of these issues... Let's stay in touch...

Rino

DCM · #36 02-21-2007, 11:45 PM

I have a 77 240d (automatic) and I get about 21 mpg in town which includes a lot of freeway miles.

My records go back about 14 years and this hasn't changed in that time in spite of my trying additives etc.

My 1980 300sd gets the same mileage but will get 26-27 on the highway.

Bama1 · #37 02-22-2007, 08:38 AM

The sounds you are describing could be the emergency brakes dragging and/or the rumblings of the worn joints of a half-axle...

A doppler-effect type thumping rumble at highway speeds indicates shaft imbalance caused by the dried-out joints and they need to be repaired before they seperate or worse yet, vibrate something else loose.

Find a respectable shop to take a quick look at both...then decide if you want to do the repairs yourself. Either one is a DIY but I elected to have someone do the half-axle replacement. - My son does great on the brakes.

rino · #38 02-22-2007, 09:49 AM

Quote:

Originally Posted by Bama1

The sounds you are describing could be the emergency brakes dragging and/or the rumblings of the worn joints of a half-axle...

A doppler-effect type thumping rumble at highway speeds indicates shaft imbalance caused by the dried-out joints and they need to be repaired before they seperate or worse yet, vibrate something else loose.

Find a respectable shop to take a quick look at both...then decide if you want to do the repairs yourself. Either one is a DIY but I elected to have someone do the half-axle replacement. - My son does great on the brakes.

Hi, I just noticed this morning that I got the same clunking sound coming from the rear (several instances of it) while jacking up the front left wheel... does this pinpoint to either a brake or half-axle issue? By the way, I don't drive the car at highway speeds... the clunking/rumbling noise happens when the car is driven slowly while making turns, or accessing the downward slope that leads to my garage.

Rino

rino · #39 02-22-2007, 10:01 AM

Quote:

Originally Posted by DCM

I have a 77 240d (automatic) and I get about 21 mpg in town which includes a lot of freeway miles.

My records go back about 14 years and this hasn't changed in that time in spite of my trying additives etc.

My 1980 300sd gets the same mileage but will get 26-27 on the highway.

So, this is getting all very confusing... there is a bunch of people that keep asserting that there must be something wrong somewhere in my car, otherwise I couldn't be getting such a low mpg. Then there are those that, like you, say my fuel mileage is normal, given my doing nearly all of my driving in a high-traffic city.

By the way, I did not mention (because I almost stopped noticing... it's been this way for two years, since I bought the car) that my idle speed gets very high once the engine gets warmed up... When I start the car with a cold engine, the idle is way much below normal, and I need to keep my foot slightly on the accelerator pedal in order to compensate for that and avoid strong vibrations in the engine compartment. But when it warms up, then the idle gets on the high side. I thought since the beginning that it wouldn't make much sense lowering the idle speed, because with a cold engine it is already very low... So what do you think could be done about this low-idle/high-idle issue? (which for sure contributes to more fuel consumption than normal)

Rino

pj67coll · #40 02-22-2007, 10:52 AM

Rino. It seems to me that your car is operating opposite to its intended method. Mine is noticably faster at idle when cold but the idle decreases significantly when it's warmed up.

I too have severe vibrations on startup and shutdown, my motor and tranny mounts are shot.

I do use the idle control knob a bit, especially so during this recent cold spell. I keep it at max for cold startup and for a few minutes thereafter and then reduce it to normal.

- Peter.

rino · #41 02-22-2007, 11:01 AM

Quote:

Originally Posted by pj67coll

Rino. It seems to me that your car is operating opposite to its intended method. Mine is noticably faster at idle when cold but the idle decreases significantly when it's warmed up.

I too have severe vibrations on startup and shutdown, my motor and tranny mounts are shot.

I do use the idle control knob a bit, especially so during this recent cold spell. I keep it at max for cold startup and for a few minutes thereafter and then reduce it to normal.

- Peter.

Then something might be wrong with my car's self-regulating mechanism for the idle speed (I have no idea what that might be). I minimize the vibrations at startup, as I mentioned, by accelerating constantly just a tiny bit with my foot on the pedal for the first few minutes (at stops, when the engine should be at idle). I'll have to repair the idle control knob mechanism, since the cable is disconnected (missing the retaining screw trap at the throttle linkage...

Rino