Hi everyone,
I'm just writing because I'm curious about whether or not my fuel economy is normal. It is always in the 20's both in city and in highway. Typically, on a pretty equal city/highway share of driving, I get 200 miles by the time the gauge needle hits the middle line. I usually figure about 25MPG or something like that. I don't know anyone else with a diesel so I have no one's notes to compare to, I just always thought that diesels were supposed to get great mileage but it's really no better than my Volvo. It'd be great to bump up the economy being as how the fuel prices are so high; I pay about $1.75 for Hess diesel. I guess it's still less than regular gas. Anyway, thanks a lot.

Alex

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

Greetings Alex,

We all wish for great mileage on our diesels and there are a few things we can do to maintain them to ensure we get all we can out of them. These are a few things to look at to produce perhaps more MPG in your case. Valve adjustments every 15,000 miles, injection pump, fuel start of delivery check and adjustment if needed, turbo wastgate checked for proper opening pressure, clean injectors and proper spray pattern, 85+ helps to increase cetane in the fuel and keep the injectors clean. These are all routine maintenance items at various mileage intervals and in most cases neglected as well. Most daily drivers don't notice the slow degrade of their vehicles until it's to late. Some tell tale signs that you aren't getting the performance that's expected is constant black smoke rolling out the tailpipe, hard starting in ambient temps, casual change in acceleration and of course mpg on a consistant basis. I for one get about 27 mpg on a non-turbo 300 model. Although I wish it were about 37 instead it's not bad considering that it doesn't have a turbo for one thing, and considering that it weighs as much a truck. The mileage is comparable to that of my 4 cylinder Plymouth that weighs a 1000 lbs. less and has not the ride like this Benz.

Charles

These people are correct take you time and do everthing correctly. I have had my 78 300cd (no T)for two years. bought it with low mileage 80,000. I have put 15,000 miles on it and have felt like I was doing all the right things and was getting 23 mph. As of 3 weeks ago I completed these issues
1) fuel additive, most here talk about redline, lubromoly, I personally use HOWES Diesel conditioner, keeps the injectors clean lubricates the Ipump, eliminated almost all visable exaust soot. makes the engine run much soother and keeps the momentum of engine up in usable rpm range with out exessive pedal.RUNS SMOOTHER
2)eliminate all vacum leaks, this helps the idle, locks, a/c and shut off.
3)adjust valves, get the right tools takes 1/3 time
4)changed from catrol gtx to rotella oil "change it hot change it often...."
5)change all filters, 2 fuel,1 oil, 1 air, 1 tank
My mileage has increaed to 28 mpg, much smoother starting, idling, running, quieter, quicker, and fixed my fluctuating gas gauge. I am not a cerified technition, or would even consider being called a mechanic, (maybe a very experienced DIYer) the only other thing that can be done is a timing chain, mine was properly measured and had did not need changing.
This milege is what is advertized for this vehicle, and at this sized vehicle, with the potential of out lasting multiple vehicles, I am impressed.this is by no means the text book of upkeep just my .02 anyone else can jump in if I have missed anything. Start with the additive, I noticed instantly! CD in SC

We have consistently gotten 30mpg in our 1980 300SD with well over 500k, up to 38 mpg on slow drives (55mph). I think it is a matter of driving a constant speed and a light foot, (pissing everyone else off on the road in order to save fuel!!!)-it also saves tires and brakes (driving slow that is). We haven't used conditioners or additives, but rebuilt the injectors every 150k or so, and use synthetic oil. I would recommend using conditioners to help, but personally find the fuel quality itself is the biggest factor and the conditioner not up to its claims. Point is, experiment with various fuels in your area and find what works best, it will be obvious by sound and miles to a tank. We can acheive well over 600 miles to a tank with local diesel, much more with southern US diesel though. Of course regular maintanace goes without saying.

These cars are great but for a diesel they don't get the best mileage. Because they are heavy and automatics.

But my other diesels did not do that much better.

1984 diesel rabbit 37 mpg around town
1984 diesel corolla 37 mpg around town (ugly but great car)
1982 diesel Maxima 33 mpg around town 46 highway

These were all 5 speeds and lighter than my 300d tank

My 1984 300d gets 27 mpg around town.

My 1985 vw scirocco got 27 mpg and weighs half the Mercedes.

It gets harder when you compare modern gasoline engines vs. 20 year old diesels. If your diesel was a gas car it would be a gas guzzler.

Diesel is better than gas engines in fuel economy but in others ways also. They don't have the maintenance demands and last much longer if properly maintained. Just change the oil often as described in this forum and you will enjoy years of motoring.

I see advertisements for new Nissans Sentra bragging that they get 35mpg on the highway. I say big deal my car could kick it but in a fight for one tenth the price and get about the same mileage.

Your diesel does not sound so far off the mark.
Do maintane your diesel and accept that 25-30 mpg is good for that car.

good luck and happy motoring

bob

PS how do you drive it
Diesel should not be driven like gas cars. It does little good to rev these engines at high rpm. They are low end torque machines. I rarely drive mine above 2700 rpm. Only at highway speed do I brake 3000 rpm. You are better served to get the car to shift earlier than later into the next gear. That of coarse is my humble opinion but diesels are different. I enjoy putting around in mine. I rarely race it unless I am getting onto the highway. That might help out

good luck

bob

I agree with "the Bob" about driving habits. If you really lean into it at every light, then your fuel economy will go down. My last tank got 31 mpg, using Mobil diesel from a gas station/truck stop. In otherwords good clean, hasn't been sitting around for a while, diesel. Like any car, stop and go driving really saps the MPG, but I think for diesels it's even more so. Think how much throttle you have to give it, compared to a gas car, to get it going. Turbos help greatly, but they don't spin up until about 2500 rpm. Slow and steady is the key, unless you're getting on the highway especially here in NJ. Here the "slow" lane is 70mph.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

Greetings All,

I'd only like to chime in on one item when speaking about the tranny shifts. If you're driving a 300 series with an auto, make sure the linkage is set to spec for shifting or cable if your has that, or vacuum if yours is a newer model. As mentioned throughout the MB manual in the tranny section, proper shift levels must be maintained or you'll end up doing more damage to the tranny than good. You are inherently trying to get a smooth shift causing the plates to slip to do it, causing wear on the clutch packs. This all too common flare between second and third gear some experience is generally caused by the tranny shifting to soon without developing proper RPM's for the next gear change. I have noticed a great difference since I adjusted my linkage as MB instructed me to. The shifts are a bit drawn out but are solidly locked in without any signs of slippage or flaring between gears. Yes, some folks will call it hash shifting, but MB developed the tranny to shift in this manner, and so be it, if it will last as they designed it. These adjustments not only help to upshift, but to downshift as well when the car is subjected to moderate inclines without slamming the downshift button to get a response.

Charles

I own a 91 300D 2.5 Turbo, 125K miles.
I like to reset the small odometer every time I fill up the tank, just to check on the milage. On my recent trip to Canada, I got about 28 mpg with 3 people in the car, airconditioning on all the way, driving 65-80 mph (yeap, I slowed down to 65 when I got a ticket upstate NY).
I noticed that it makes the GREATEST difference if I use the cruise control to maintain constant speed. The maximum mpg I can remember getting was as much as 35 mpg in a long trip 3-4 yrs ago. Airconditioning, speed and cruise control seem to make the biggest difference for me.

I like the look in the eyes of people though, when I tell them that my MB goes up to 500 miles with one full tank of diesel !

For what it is worth, I always notice about a 10% fuel mileage increase when I pour a can of STP in with the oil.

__________________
'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles

24 MPG is probably average for the 300D. My '78 runs about 24 MPG with best observed of 26 MPG. If you have the MB Manual, it gives the specs for fuel mileage as well as oil use etc. You'll find that 24 is probably about right, but it depends on drive habits/style. Granted, valve and IP timing might help you and some redline but you won't get in the 30's like the turbos or the 2.5L.

Sorry, that's the only negative I can see for these cars (& not a big one when you consider the size and the ride!!)

Good luck,
Rich

On my 83 300D I averaged 32 going to and from work. it is rural driving. And would get 34 0n the highway as long as remained under about 64-65 miles per. Over that it would drop to 28 until i hit the 75+ and it went to 24.

My 86 300SDL gets around 28 inthe same drive to work, and 30 highway, doesn't seem to be effected by the higher speeds. It usually has not exceeded the 75mph since I have not been through Montana lately so I really don't know what she would do at 85+.

Ric

My 87 SDL is doing about 29 in town and 32 on the highway. When I purchased the car I installed a K&N filter. I don't have any before and after mileage numbers for this car with the K&N application.

The K&N did however have a great effect on my 94 Suburban jumping the highway mileage from 13mpg to 17mpg.

FYI: Montana's back with a state speed limit.

I haven't seen above 20 mpg in southern california on my 84 300SD CA 254K

Of course, i drive fast with quick accelerations, and AC on all the times?

Is this unusually low compared to what others have seen for this car?

I know I'm a little late on this thread, but here's my story. I don't know how big the tank is on my car(80 300cd) but when I fill up at around 440-460 miles it takes 19 gallons. That's 50/50 city/freeway to and from work. The fuel light comes on at about 440 miles. While on my latest trip from WA. to AZ. doing 70mph(the car just seems to like that speed) for about 1600 miles, I was filling up at about 460-480 miles per tank. I just need to know how big the tank is and how much is left when the light comes on. thanks , andy

My chart lists that car with a 21.1 gal fuel tank.

__________________
'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles