What's the secret - Poor Mileage on my 300SDL - PeachParts Mercedes-Benz Forum

wgilmore · #1 02-13-2009, 01:26 PM

I know this topic has probably been virtually exhausted and low on interest but I can never get the Fantastic MPG that so many of you get on your 300SDL's.
My city mileage is about 19 and highway about 21.
Everything reasonable has been gone through on this engine -
No emission junk
New Catalyst
No ARV or EGR
Bypass ALDA circuit crossover valve
Pre-Chambers clean and fine
Injectors Fine
IP in time
Waste gate closed
Have reworked the head
New chain
Everything is clean - intake - exhaust
Everything is sealed

Have not measured boost under load.

What am I missing or is everyone else by chance getting better mileage.

awsrock · #2 02-13-2009, 01:31 PM

Odometer slow? That's all I can think of, really.

Having no boost might keep your mpgs down, but I wouldn't think more than 1-2 mpg at most.

How much do you drive in city traffic? I have been getting really bad mileage in my 300D with the combination of shorter trips and the ridiculous cold we've been having lately (although this week has been very nice!)
Still doing well on the highway, even with winter fuel (I assume it is winter fuel)
21 hwy is definately low, though.

wgilmore · #3 02-13-2009, 01:55 PM

Quote:

Originally Posted by awsrock

Odometer slow? That's all I can think of, really.

Having no boost might keep your mpgs down, but I wouldn't think more than 1-2 mpg at most.

How much do you drive in city traffic? I have been getting really bad mileage in my 300D with the combination of shorter trips and the ridiculous cold we've been having lately (although this week has been very nice!)
Still doing well on the highway, even with winter fuel (I assume it is winter fuel)
21 hwy is definately low, though.

I have had the odometer repaired , then replaced , and now am getting some trip odometer gear noise. The noise comes and goes. I haven't been too concerned about it since the gears are all new, however the speedo input is a square wave pulse that gets amplified to generate the movement of ... I can't recall what element , but it's reasonable to get some noise at low speed. I will though check the speedo / odometer again this weekend.
Will check boost this afternoon and report back.
I think we are getting a mix of No.2 and No.1 here until march , then we get straight No.2.

Just amazing some of the reported mileage that I don't approach - like 30 ...
come on everyone ... 30 mpg, 28-29 city... not my car.

TX76513 · #4 02-13-2009, 01:57 PM

Here are some things to consider:
You stated the injectors are fine. Have you pop tested them or checked the spray pattern?
You need to check your boost or at least what is your 0 -60 time to get an idea of performance. These beast are even known to get a clogged exhaust.
How is your IP and Cam Shaft timing?

Some food for thought.

wgilmore · #5 02-13-2009, 02:14 PM

Quote:

Originally Posted by TX76513

Here are some things to consider:
You stated the injectors are fine. Have you pop tested them or checked the spray pattern?

No. I know I should, since I could have a dribbling injector or one that is early or late..
But the engine runs and starts so well , at idle and cruising I just didn't consider and injector as a problem. I did just disassemble all of them and cleaned them well. I do know they are a wear item though.

Quote:

You need to check your boost or at least what is your 0 -60 time to get an idea of performance. These beast are even known to get a clogged exhaust.

Will check my boost think afternoon.
I just had the trap replaced with the catalyst about 1500 miles back, had the the entire exhaust system off, including turbo, gutted the muffler basically (the one under the rear bumber).What should a good zero to 60 be.?

Quote:

How is your IP and Cam Shaft timing?

Just checked the IP timing last night, it is fine at 15* ATDC.
Cam shaft timing - don't know what you mean, the cam lined up to cam marks with no.1 cylinder at TDC is 2 * on crank . Is that what you mean.?

redassag00 · #6 02-13-2009, 02:19 PM

I get 21-22 mpg in the city with my car, and thats a lot of Stop and Go driving every day.

jcciem · #7 02-13-2009, 02:27 PM

At this time of the year (wintertime fuel) mostly city/town/village/hamlet driving average economy of between 19 and 21 isn't unreasonable. Highway driving exclusively wintertime fuel , you should be getting 23. However summertime fuel all city/town/village/hamlet your minimum should be 23. Highway, summertime fuel, you should get 28. How people get 30 mpg in a 300SDL is beyond me. I never have, and I've owned two driven for a total of 175,000 miles. Both get the identical mileage. Driving style probably has a lot to do with it.

'91 350SD 535,890 destroyed in a crash 1/23/09
'87 300SDL 252,995
'94 SL500 45,000

wgilmore · #8 02-13-2009, 02:34 PM

Quote:

Originally Posted by redassag00

I get 21-22 mpg in the city with my car, and thats a lot of Stop and Go driving every day.

I'm glad to see that I'm not the only person who gets near "EPA" , "Estimated" mileage from this car.
I sure would like to know the secrets of the 30 MPG SDL's though.
Perhaps it's a proprietary thing, special access required to gain entry into the 30 MPG world.?

wgilmore · #9 02-13-2009, 02:41 PM

Quote:

Originally Posted by jcciem

At this time of the year (wintertime fuel) mostly city/town/village/hamlet driving average economy of between 19 and 21 isn't unreasonable. Highway driving exclusively wintertime fuel , you should be getting 23. However summertime fuel all city/town/village/hamlet your minimum should be 23. Highway, summertime fuel, you should get 28. How people get 30 mpg in a 300SDL is beyond me. I never have, and I've owned two driven for a total of 175,000 miles. Both get the identical mileage. Driving style probably has a lot to do with it. I've received many speeding tickets over the years
95 in a 55, 75 in a 55, 80 in a 55, 81 in a 55, those are just the ones I remember. So if your driving style is similar to mine your mpg readings are not out of line.

'91 350SD 535,890 destroyed in a crash 1/23/09
'87 300SDL 252,995
'94 SL500 45,000

Yes, unfortunately I have never achieved 28 mpg in summer, highway driving exclusively. Perhaps stretching a bit , maybe 22 mpg in summer all highway.

Of course I'm always sure to keep my tires at 40-42 PSI (rolling resistance) and I don't have dragging brake discs.
The trunk is kept clear of junk to keep weight down and I always insist that my wife eat a light meal, bring her smallest purse (26 lbs) and no jewelry if riding with me in the SDL.
I'm baffled (or perhaps my car is) as to how to get to 25 mpg in summer / highway only.

awsrock · #10 02-13-2009, 03:13 PM

Some other ideas..

Is your ac constatnly on? Perhaps the compressor never shuts itself off?
What rpm do you usually shift at? If you are going past 3k all the time, that would certainly reduce mileage.
Are you running stock tires? Wider tires should also reduce mpgs somewhat.
Alignment?

wgilmore · #11 02-13-2009, 03:32 PM

Quote:

Originally Posted by awsrock

Some other ideas..

Is your ac constatnly on? Perhaps the compressor never shuts itself off?
What rpm do you usually shift at? If you are going past 3k all the time, that would certainly reduce mileage.
Are you running stock tires? Wider tires should also reduce mpgs somewhat.
Alignment?

A/C system is OK.
I have done a large amount of work on the A/C system and so it does cycle properly.
I don't really notice the exact RPM point where shifts from 1-2, 2-3 and 3-4 occur but it is generally below 2K rpm
Am running stock size michelins, fully inflated.
I'm not sure about 4th gear cruising rpm though , I find that at 70 mph I am at 2600-2700 rpm, varies quite a lot base on load.
How does that compare to your 70 mph rpm level?

awsrock · #12 02-13-2009, 03:39 PM

That's about where I am at 70, also. I think we might have different final drive ratios, though..regardless, sounds right to me.

You've got me stumped! There are many others on here with more advice than I can give

wgilmore · #13 02-13-2009, 03:47 PM

Quote:

Originally Posted by awsrock

That's about where I am at 70, also. I think we might have different final drive ratios, though..regardless, sounds right to me.

You've got me stumped! There are many others on here with more advice than I can give

I appreciate your input . Perhaps an injector dribble / spray pattern problem or an early or late pop from an injector might have more influence on mileage than I imagine.

brandlj · #14 02-13-2009, 03:51 PM

I have a 86 300sdl that gets about 24 mpg in daily winter driving. Mix of city and highway. In the spring and summer and fall I get 25-26mpg in the same driving mix. I did get 28 mpg one time on a 300 mile drive on the interstate at 70 mph. Mostly 25-26 though. I only have 115,000 miles on my car and you have double that. How is your compression? What kind of oil? I use Mobil One Truck and SUV turbo 5W-40 synthetic.
Do you drive with a heavy foot? On my car in normal traffic with a light foot it will shift into 4th gear by 22 mph.
Good Luck in you quest. Oh by the way I run around 32 PSI in my tires. And 70mph on the interstate is 2900 to 3000 rpm on the tach. Maybe your odometer is off.

compu_85 · #15 02-13-2009, 04:26 PM

That sounds like the economy I get out of my 350. One one tank that had lots of AC usage and 2/3 city I only got 17 mpg

I never saw over 22.

-Jason