I purchased my 300SDL in April of 2003. I have always kept track of the mileage and usually get 22-23mpg city and highway combined (9 miles traffic and 10 miles freeway each way for work). I fill up usually between 1/4 tank and the Reserve mark and that is 400-425 miles. I have seen reviews of 86 and 87 SDL's online and some others post that theirs is getting 35mpg (which i don't believe), 28/30, or 25/28mpg. Mine is just under 300k miles now. If everything is working as it should (and it feels as though everything does) what mileage should i be getting. If my 22-23 is abnormally low, what should i look at first? When i first bought it I ran a bottle of injector cleaner for diesels but there was not noticeable increase in mileage.
TIA,
Shannon

With this engine, its very dependent on how much you get into the turbo. Both when you take off and when cruising. I get 29.5 on the lighter 300D.

It would do better at 55-mph highway speeds, because the turbo is barely doing anything, but I run faster up the Interstate.

So, if you are light on the pedal I think you should get 25 mpg or better.

If it bothers you to be at 22 mpg, then there are things you could check. A dragging brake caliper or two would hurt a lot. Do you see black smoke behind you on takeoff? If so then you're wasting fuel with this engine. My smoke diminished with a fresh air cleaner. You may also have an air restriction in your crossover pipe and intake manifold due to oil/soot caking. EGR disabled? Check your timing chain stretch?

Many little things to try.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

>>Do you see black smoke behind you on takeoff? If so then you're wasting >>fuel with this engine.

I only notice black smoke if i am keeping my foot in it from off the line, especially just before it shifts. With normal driving, i do not see black smoke. At times, it do see very light whisps of light blue, and at night i can see the exhaust from the headlights of the car behind me, but for the most part, in daylight, there is not visible exhaust.

I'm generally considered to be the top dog with respect to SDL fuel mileage right about now.

As a reference, both Hattie, Alan Hamm, and Smooooth get about 25 mpg with their vehicles.

I've got the vehicle up to 29-30 mpg. This average has held up over the last three tanks. The vehicle runs 85% highway and 15% city.

Several ideas:

1) City mileage suffers dramatically if you drive the SDL like everybody drives their *****box. If you have to get to the next red light, in a big hurry, only to absorb all the energy of the vehicle in the brake calipers, then you cannot get decent fuel economy with a 3800 lb. vehicle. Keep it rolling and don't use the brakes. It takes some practice and some patience, but, you must do it if you want better fuel economy.

2) Start using about 12 oz. of Power Service in each fillup. You will probably get another 1.5 mpg from the Power Service. It will pay for iteself.

3) You cannot get 29 mpg if you drive at 70 mph or above on the highway. If you wish to keep it at 68 or below, you can get better than 23 mpg.

4) Make sure the EGR is disabled.

5) Stay out of the turbo. This uses a ton of fuel and you don't travel very far.

6) Make sure that you are running at least 32 psi in the tires. 35 psi is even better for fuel economy, but the ride suffers.

7) Synthetic oil should probably give a slight benefit.

Please note however, that an engine with 300K on the clock is generally not going to get the same fuel economy when compared to an engine with 125K on the clock (mine, estimated ).

Also note that when the winter fuel arrives (very soon), mileage numbers will drop like a stone (4-6 mpg).

Someday I hope to have my name added the the list behind Hattie and Alan........(DON'T FORGET GSXR!!!!)

My 300SDL gets a good average 25MPG around town. Average means I've seen 23 through 27.

On the highway I have yet to see 30 - but come close. I did repair the Cruise Control, EGR is in "TEST" mode, and now on the NYS Thruway traveling with the crowd at 75 I have seen 28-29.

History - 87 300SDL, 170K, Previous Owner was original owner and is now 70 and only drove it in the summers. I am still cleaning out the intake system and have yet(but will this week) do a Diesel Purge. Performance was LOUSY from day one until I started the cleaning process.

My Opinion - Yes - This is a BIG car (The Big Dog) - and anything above 25 and I will be glad to do the Snoopy Dance.

OFFER!!!! - How about a SDL gathering at my place - Central NY??? The lawn is huge, the food is good, and if we do it next year - then the pool will be open(closed for this year - duh....) Let's make a weekend of 'Wrenching' out of it??? Line 'um up and go to work!!!!!!!!!

Stephen

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98 K2500 Suburban 6.5 Luxo Barge

"We cannot change the wind - But we can adjust our sails"

Hi Shannon,

Brian has a good list there. I wouldn't believe claims of 35mpg on an SDL either. I can routinely get 30-32mpg in my W124 300D, on summer fuel, with everything in perfect working order at 251kmi. I have heard claims of up to 34, which I could believe if speeds are kept under ~55. BTW, I can still get 28-30mpg at a steady 75-90mph. Fuel quality can affect MPG more than the weight of your right foot. I lose 5-10% (1-3mpg) with winter fuel, it goes back to normal come springtime. Also, if you live in CA, you'll suffer about 10-15% loss in MPG due to the moose piss they sell as "diesel fuel" in the Golden State - year 'round.

Anyway, as Brian has proved, 28-30mpg on the larger W126 300DSL is possible. Personally, I'd be hoping for 24-26mpg on your commute cycle, and 26-28 on freeway trips. Maximizing MPG takes a lot of tweaking - filters, IP adjustments, tire pressure, yadda yadda. If you're in CA, the MPG you're getting now may be about all you ever will get.

BTW - a bottle of injector cleaner may not do much to help things. It won't hurt to try though. Also, a small puff of smoke out the rear when leaving a stop is NORMAL and indicates a properly adjusted IP/ALDA. A cloud of smoke is not normal and indicates wasted fuel (and maybe a dirty air filter.) Finally, I once experimented by driving a whole tank with a lead foot around town, to see how much MPG would drop being "in the turbo" all the time. To my surprise, the reduction was much less than I expected - about 5% or so (1-2mpg less than 'normal'.) I'd recommend anyone else who routinely tracks MPG to do this for one tank, to prove it to yourself! You won't go from 28 to 22 with a lead foot, ever... it takes hours of idling or a fuel leak to do that.



HTH,

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Dave
Boise, ID
Check out my website photos, documents, and movies!

The recent prices (2.31!!! ) have caused me to be more slow in my driving style, slow take off....lots of coasting to lights, and so on. When I drive in my super sporty style I don't even think I get 19-20 in the city.......being a snail I have gotten it as high at 26-27 though. Which is pretty good.....that is with an SD however, I don't know what the difference in fuel efficiency would be between the SD and SDL, is it much?

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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)

Fuel economy difference between the SD and SDL is probably 10-20% when they were new - could be worse now, as some older 617 engines seem to have trouble with decent MPG for some reason (I have one of those and it's really frustrating.) I doubt you'd see many (any?) SD's hit 30mpg but I'm not that familiar with them...

Dave is correct.

I never achieved better than 28.5 with the SD, and I certainly cannot hold that figure. 26-27 is the norm. The 617 is not as efficient as the 603.

That's optomisted as all hell on the weight, my scales at work say I'm 3780 with me and under a quarter tank of fuel in my w123. I've never seen under 25mpg, and I have a LEAD foot on takeoff. Best has been dead on 30mpg running 80mph north up I-55 I believe it is for a 300 mile stretch. I can get 28 if I want to impersonate the old VW diesels.

And I bet mine's faster than a w126.. :p

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

Correct. Weight is zero fuel and without driver. Revise the rolling weight upwards accordingly!

I average a pretty steady 23.5 with 12oz's of Power Service. Their heavy cars low 20's around town is very good.


Smooooth I'm in I could go for a nice road trip!

I bet the average SDL weighs about 4,200 pounds. Figure 400 for fuel, driver and "stuff".

Still light by W140 standards!

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

3835 pounds empty, 3820 for the w140

Let me check quickly. I go 575-600 miles on a tank, 20-21 gallons at fill up.

Let's see, that's 27-30 mpg. Yep, I'm normal. Whew!

Um, I make two 180 mile Interstate trips per tank at 65-75 mph, ususally set the cruise to 65, sometimes 70, depending on average traffic.

The rest is around town stop/go 34-45 mph, and a bit of rural 55 mph.

Haven't gone through a winter yet with winter blend #2.

That's awesome. I can go over 650 if it's all hwy. I have never gottne more than 470 in the city, driving like my Mom.

425 is generally the norm for city driving, but I do drive fast all the time.

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