How the $%$## do you get 30 MPG?
 

I have an 86 SDL, and I have read repeatedly about people getting 28-30 MPG. I get 22 religiously. Are these people lying, or do I need to do something? The air filter looks good, but beyond that I would not know where to look. Since I am new to diesels I would appreciate the help.

Oh, and I did a search, but searching for MPG or mileage brings back about 1000 different threads that seem completely unrelated. If you feel so inclined I would also take some pointers on how to search for the answers. I don't want to rehash all the same threads over and over again.

I guess they roll down hill, with a tail wind. The trip to and from the destinations are always downhill...Just a guess. I get 28 in my 300D, and that is if I keep my foot out of it.

now i get 28-30 with my sdl but i have no ac It gets as low as 25 in the winter. My fathers sdl seems to hang 24-26 year round with working a/c
Dont ask me just the way it is

28 mpg highway?

I get 22 city since thats all I drive and I romp on it

Yep, Highway. Since I live in the sticks, I do not have to endure citiy driving very often. When I do have to do city driving, the mixed result is 24 mpg.

trip from Maine to Virginia I consistantly got 25mpg+ at 75-80mph, and i have an injector that isn't popping correctly.

I'm assuming you've adjusted your valves, checked for timing chain stretch, and checked your timing??? Valves can be a biggie.

Many cars from that era have major problems with the accuracy of their odometers later in life.

Someone who confirmed their 30mpg using GPS would be impressive, although I would still be dubious as my E300 which is 2 generations newer technology only manages 31mpg combined city/hwy and it is mucd more efficient areodynamically and drags around less weight.

Valves, change the diff fluid, make sure the tyres are inflated. With one of those BigBoys, you should be near 26-ish.n If you;ve never run any cleaner through the fuel system, its not a bad thought.

Remember, you wont get the 700+ miles on 20 gals that we get with our smaller more "modern" cars. So keep your references STRITCLY to the SDL line with the big 3.5L engine.

Now Terry has me wondering if my odo is shot! I'll say this,. it got the best milage running straight D2 out of the pump, which rattled the heck out of the motor. With bio in the mix, it runs MUCH better but milage dropped slightly to jsut under 700 miles/tank. And then with the AC on ( lately around here), it dropped again, to around 30.

I get just over 20mpg city on WVO/Diesel mix. I can get as high as 25 on the highway.

went from 24.95 to 29mpg - 300SD
 

My 5 cylinder 300SD went from 24.95 mpg to 29 when I replaced the
broken odometer gear (the 12 tooth gear).

It had 10 teeth.
Funny, I was getting about 400 per tank, cruising speeds seemed okay.
I thought I was driving 66 miles to work each day.....

The 300D gets 25mpg consistently, odometer has no broken gears.
But that engine has no turbo.

Not having a 6 cyl engine like your SDL don't know what to expect.
But that timing of the injection pump is critical. Although, I have never
adjusted mine.

I too get baffled by some of the mileage claims. I used to be told that the
300SD would get 33mpg. Never seen that.

My ODO so far is correct. I have a 2 mile speedo/ODO check spot set up by the state of Texas on HWY 34 Between Quinlan and Greenville TX. It is not on my normal route, so every few months I go to Quinlan for lunch to do the test. I do not know if the ODO in my car was repaired or not. I do not have 1st owner records. 2nd owner records do not indicate any ODO repair.

redassag00 confirmed 31mpg on the trip to Centerville with his GPS in his 1987 300SDL.

i got 28 when driving 65mph for 9 hours.... i get like 22 in day to day life, dang city and traffic. but thats life

as far as searching goes, do not bother with the search function on this site.
Brian Carlton explained and approved method: http://www.google.com/advanced_search?hl=en use the advanced search link, type all the words you want to search for, then restrict the search to www.peachparts.com Domain.
perfect searches every time!

Sheeesh thanks for the tip! I was feeling like captain Tard Boy in my searches!

Oh, on topic..... 28 MPG 300D turbo

Highway and speed means everything. Here in Texas - no hills and no turns. Cruising on a pretty day with the AC off at a "reasonable" speed and you can get the most mpg of any car/truck.

and, it was on topic, he had 2 questions, one was about the mileage, the other was about the searching... but to give you a topical answer on my experiance, NO IDEA... neither of my cars have working odometers...

So what,. I reckon that the huge drop in milage with the AC on is natural wiht these or is something amiss with my 95? You can certainly hear the compressor on, and in fact, its is THE soundtrack from WWII movies for any military truckmoving about, a whirring "geary" noise. ( and I kinda dig it) System checks OK, cools like stink, but had a high pressure issue when I was romping the heck out of the engine. ( AC would turn off )

Running AC off though, is major milage zone.


BTW, as a numbers guy by trade, I have to say, I wont quite milage. Yet. Why? Too few datapoints, too many exogenous variables. Fillup repeatability, weather, etc. And many of us are relatively new to these cars., so still have few datapoints. But I can see the range differences per tankful pretty clearly. Nonetheless, its easy to get an "outlyer" with mpg calculations/measurements, so much of the exaggerated milage is likely numerical outlyers.

Or out right liars. ;)

'83 SD, I get 29 mpg mostly highway (no A/C windows down, sunroof open), I check odo against the Interstate markers, pretty close. Dino only, WINGAS, bio. etc. I understand does not have as much energy in a gallon, meaning you will not get the mpg you will with dino. Same thing with blended gas (ethanol) in cars, the energy is not as much as gasoline = lower mileage. I drive 70 (65 Interstate) miles a day going to and from work. The valves have been done before I bought it, Nov. '06, I have replaced the fuel cap gasket, some would slosh out during left turns, and now I'm, at least on the way home, driving at around 2500 rpm. (55 to 60 mph) According to MB, that is where THIS engine makes maximum torque, which will give the best possible mileage.

1987 300SDL, 135K

Nashville to Little Rock round trip average 28.05 MPG. Almost all highway on I-40 at 70-75 MPH. Some construction and traffic around Memphis, some town driving in LR. A/C on. A few big hill climbs on the TN side.

When all city…….22 to 24MPG, mostly light-foot with A/C max.

I think this is great for a big, safe, family cruiser car. I could almost double that in a TDI Jetta, but I would have to drive a Jetta to do it……….. Driving a Jetta would have saved me around $35.00 on the ~700 mile trip. Not worth it to me. I am not able to calculate the environmental or foreign oil dependency impact of my decision against the Jetta ;)

Just a note, you can get better mileage, it appears, by using B20 (20% biodiesel mix).
That way you're getting the better lubrication of the bio while not sacrificing the higher energy content of the Diesel.
It's only a 1-2 MPG improvement, but it is an improvement.

B100 gives 2-4 MPG worse than D2.

My non turbo 1979 300CD, gets a consistent 30 to 32 miles per gallon. On the other hand, my 81 300CD turbo car, has never done any better than 25-27 miles per gallon.. I don't know a lot about the diesels yet, I'm still learning. It's weird, but I guess some do a lot better than others.

Thanks all, this has been a fun thread to read. Keep up the answers, it is interesting to see the varied responses.

On a seperate note, I thought that the 86 and later cars did not need a valve adjustment as they had hyraulic adjusters?

Some responses have mentioned adjusting the valves. This is not necessary with your engine, which has self-adjusting valves. Your engine, the OM603, only appears in the 86-87 300 SDL and the 87 300D. A bigger version is in the 90-91 350 SD/SDL. So really, you only need to compare your mileage to other 86-87 SDLs. Even so, most seem to report considerably better mileage.

You say the odometer is OK - that's good, but I'd still look at a longer drive of a known distance. Odometers have been known to slip sporadically. You also need to make sure the tire size you have on the car are roughly equal to what originally came on the car, otherwise you will have to adjust what the odometer is telling you. Of course, make sure your tire pressures are good.

You say you're new to diesels - well, they respond well to robust treatment. You may due well to allow the engine to get good and hot, then put a full load on it by driving up a long steep hill. This will allow your vehicle to burn out any carbon build up that may be in the engine. You also may want to look into running diesel purge through the car. Many report better mileage and smoother idle after this treatment.

Speed is important with these cars. I think the torque peak in top gear with your car is at around 65 mph. Generally speaking that is the point at which you will obtain your best mpg; going faster or slower in the same gear will result in reduced efficiency. Somewhat surprisingly, most report running the A/C doesn't result in a big change in mpg.

Good luck.

If you have a 603 engine? I don't know what the SDL from 86 has but I think most SDL's have a 603 in them. If it has the 603 then yes... no valve adjustment because hydraulic lifters. Also, many people here are not driving the same car/engine as you and are commenting on their MPG's. Not that that's bad but obviously they will get different fuel economy than you will.

There's more than the air cleaner also to check. Things like EGR, Turbo shaft spinning freely, etc. Probably a much longer list than I could give if I sat and thought about it for even 10 minutes here. But that's what I'd do. Look around and make sure everything is working.

Torque peak has nothing to do with mileage, little to do with anything really. What will tell you the most efficient RPM would be a BSFE curve, and to take full advantage of that you would also need to be able to re-gear.

You will find that your car will get better mileage the slower and smoother you drive, provided you're in top gear. The largest consumer of power while driving is wind resistance/drag, the increase of which is logrithmic with regard to speed increase.

Significant contributors to fuel mileage will be first speed, then how clean you're running (windows/sunroof open increases drag, so would a bike rack etc.). Tires are important, good round tires as well as proper inflation, and although ride and handling could suffer the harder the better up to the sidewall max. inflation if mileage is the only goal. Wheel alignment is important, the more the wheels are creeping sideways to go straight the more fuel burned, brakes dragging will cause same, and yes, the A/C will make some difference.

In the winter as one has mentioned here, the winter blend fuel has less energy content, so less miles/gallon, engine tune will matter, even good engine oil will make some difference, as will whether your fan clutch is completely disengaged.

The last thing I'll mention is fuel leaks. It is surprising how much difference can be made in fuel mileage if you have a couple of injector lines seeping a little, 60ish miles of leaking takes about an hour, how much will a couple of leaking injectors leak in an hour?

Brian gets around 30 with his SDL on summer fuel. After seeing how he does it I beleive it. Here is how:

Shut down the AC.
Drive on nice flat open roads for 400 miles, at 65-70.

You will get about 30mpg.

Drive around town you will get low 20's.



Lots of diesel drivers lie about there mileage. I have had people swear up and down that there 300D got 40mpg and there 240D never less then 35mpg.:rolleyes:

I don't pretend to understand everything, yet power and torque are forces that have a great deal to do with engines. Check this out. http://craig.backfire.ca/pages/autos/horsepower

In my 83 300SD 216k, I got 28mpg+ the last time I checked. This was on petro, mostly highway with a little city here and there. The odometer works, at least it indicates the same distance as google maps tells me it will be to get places.

The valves were adjusted by a previous owner 6 or 7 years ago but in general the car seems to have been neglected/abused since then... my A/C doesn't work, so none of that... other than that, I don't know what makes it relatively good. Luck? My old 300TD Turbo got in the lower 20s, but I have since realized after reading some more that it probably needed a valve adjustment.

I'd be interested to see what I get on this tank, which is about a B33 blend.

The 87 300D I had got between 27 and 33 mpgs. Pure highway driving got me the 33 and mixed driving got the 27. This was a car with over 250K on it.

in a 240 i got 20 around town. nothing but short hauls of a few miles here and there. with any of the 3.0 liter diesels with turbos I never could get near 20 around town. more like 17.

the 22 highway doesn't sound that bad really.

best I ever got in a turbo 3.0 was around 25 with any consistancy, and that would be on trip with max speeds of 65. running 75 it is more like 22 23.

folks seem to get better mileage in colorado and places with high altitude.

Tom W

summer trip on WVO and B100
 

This Friday morning , my wife and I are leaving for Vermont and then onto Bar Harbor, Maine in our '82 300D. We will be running the longest legs on 100% WVO and around the towns we will be running B100. I will confirm the mileage on a Garmin GPS Street Pilot. It should prove interesting to see what mileage numbers I can attain on WVO and B100. The total trip should be around 2000 miles.:)

I took a trip two summers ago from vermont to virgina.. on the way down i was hurrying and keeping up with traffic, and got 28MPG... a week later on the way home I went about 700 mile on 20 gallons fo fuel...( all highway driving, NO stop and go other than a rest stop every 2-3 hours..)

May be my odometer is wrong, may be my injectors are not set up right... may be... but I changed only one thing on the way home:

Now for the punch line, It took me 16 hours. including stops. I was driving that speed because the radiator was marginal, and keeping the tach at 2400 RPM seemed to keep the tempature down(about 53mph)... yes it was economical, and my math figured out to be about 34.9MPG.. Regardles of if the math was right, it was an improvement over the calculated 28MPG I got on the way down. the only the drivers habits changed... used to get about 25MPG in mixed driving, but not any more for some reason..

I Bet as Hattie suggests, Brian drives in a manor which places as little demand on the engine as one is able..

I get 25MPG in the wagon and 28MPG in the sedan.

Going beyond that seems doubtful (with all that I've tried).

The '83 SD that we got rid of last year got about 24 with the AC running, and a solid 27 without. This is overall mileage, which is 90% highway if not a bit more.

My '96 E300 gets 32 overall with the AC running, under the same conditions. The new Jetta TDI gets 42.

We're pretty anal about checking fuel mileage with each fill-up, just to see if something is wrong with the car.

How? Get a 300d
 

I get about 36 on the highway. :D

1991 300d

I had one that tricked me for a long time, until I clocked a trip I knew the exact, real miles of. It turned out, the car clocked about 21 extra miles, on a 52 mile trip. So, I was able to tell that the speedo/Odometer, was working faster than actual miles. The car told me I was doing like 45, when I was actually only driving about 32 miles per hour...Big difference..

Try like 1,200 rpm off the line, maybe 1,500.

If I drive like Brian I can et 24mpg around town, but I'm in a rush so I'll live with 21.:D

well I haven`t been able to achieve the 40 mpg I saw on e-bay tonight
on an old 300 cd with 396000 miles.

but starting back in march 7-07 through july 2-07, my mpg are as follows:

28.27 28.46 23.00 29.06 25.61 27.99 29.20 29.38 28.52 27.77

28.65 30.83 26.31 28.08 27.45 26.33 29.16 28.72

this is on my CA 85 300D, but with all the junk removed and changed
back to like an 83 so it can breath.:D
that last milage was at 330868 miles just before the chain gave way.
Charlie

I think a well running 85, with a 2.88 differential, and a well maintained engine, should be able to get high twenties on a regular basis. I've gotten anomalous readings as high as 33 mpg, that was on a trip from pennsylvania to north carolina, on 95/85 driving 80-90 mph most of the way. But as I say I think I hit a dimensional portal of some sort, or else hit an errant pocket of frictionless asphalt. Mostly when I make this trip, and I've verified with GPS, I average 22-25 mpg, A/C blowing until it gets too cold an I have to open a window.

Because of the 2.88 rear end, the 85 300D and 300SD get the best mileage around 75 mph. I have achieved 28mpg highway on straight no. 2 diesel with my 85 Cali 300SD after replacing the muffler with a cherry bomb and modifying the turbo with a 50 trim compressor wheel. This is very good for an 85 cali car.

I believe that running power service in each tank is cost effective as a means to increase mileage in these cars. Adding power service to no. 2 diesel will boost your mileage more than it will adding it to no. 1 diesel.

I agree, Brian and I have both noticed this.

Interesting statement, and what data was used to calculate this?

One can assume then that the 2.65:1 diff therefore create a need to drive 81.5mph for the best mileage?

I can see it now.......

But officer! At that speed I get the get fuel mileage! REALLY!! You would not want me to waste fuel now would you? Or are you one of those that like dirty air?:laugh3::rolleyes::D

Pump Error?
 

I put diesel in a station on my way to work, and I calculate my mpg every time I fill up. One pump in this station always give me 29 - 31 mpg, whereas the others give me between 26 t0 28 mpg. I always fill-up the same way so I know this "special" pump is somehow giving me more diesel. I know the pumps are checked by the state for accuracy, but I'm happy the way it is.
My work car is an 1987 300D.

I would say that that is scientifically impossible. It certainly flys in the face of all experience that I have had, and I have changed quite a few rear diffs to improve mileage, etc.

A higher speed will always require more power. More power requires more fuel.

Now a higher ratio rear end will produce better fuel economy at a given speed, though.

Tom W

Apparently my sarcasm goes unappreciated. My earlier statement reflects my real observations on the subject, and I agree that to a point, taller gearing will improve fuel mleage.

Just changed both front wheel bearings.

I have no idea how much my mpg has increased,
but I do know it will due to this change as the car
is MUCH slicker rolling now. Before it felt like my tires were going flat.
I travel much furthur after letting off the gas now.

One bearing was making only a tiny grind noise.

Low milage can result from a number of things. First, make sure you don't have any fuel leaks. Bad overflow lines can leak off enough fuel to drop you a couple mpg without leaving much fuel dripping off the engine.

Leaking fuel lines can cause air to enter the injection system, resulting in lousy combustion, hence more fuel used per hp output. Dirty injectors, carboned up prechambers, late injection timing, and so forth will also reduce the hp produced per unit of fuel. An Italian Tuneup (drive it like you stole it, for example) will work wonders. So will a hard several hours on the interstate.

You also need to verify that you do not have dragging rear brakes -- they can cost you up to 4 mpg before you notice much preformance loss, maybe more. Probably time to rebuild calipers by now anyway, they get "sticky" with age due to bad rubber seals. Bad front end alignment will eat fuel (and tires, look for uneven wear, especially inside or outside of both fronts). You usually notice dragging front brakes as they are never even and it causes the car to pull sideways. Other worn front suspension parts will cause the same trouble without excessive tire wear as it evens out more.

Old sticky diff oil will cost you milage, so will crappy tires, or tires that are out of round or out of balance. Inflate to the max numbers listed in the filler flap, it helps quite a bit.

A slipping tranny can cost you milage, of course, but so can driving style. I get 32 in my 87 300D is if stay off the turbo, 29 if I don't.

My brother gets between 27 and 29 in his 86 SDL, no AC. 30 would be unusual, its a rather heavy car.

Peter

Three words: fuel line magnets!!!

LOL