exceptionally high mpg 116 sd? - PeachParts Mercedes-Benz Forum

bruiser · #1 07-20-2005, 10:46 PM

after two tanks in my '79 sd i'm getting around 28 mpg. granted, these are about 70% highway miles (@70-75mph), but it is even higher than expected. my engine sounds really good, you don't know it's a diesel unless it's idling (and even then it could be mistaken for an old gasser), no smoke at all with the exception of when you really punch it, but this is a few mpg higher than what i expected. i drive fast, but i don't drive hard. what are others getting in their 116 sd's?

i'm going to have the valves adjusted next week (first time i'm leaving it to a professional so i know how it should sound and act when properly adjusted), service records show 30k since the last time, will that increase the mpg even more?

i'm really digging this car thus far. once i get the cruise fixed and a bulb for the tach it'll be mechanically flawless (jinx).

t walgamuth · #2 07-20-2005, 10:48 PM

i would suspect speedo error. do you have low profile tires?

pawoSD · #3 07-20-2005, 11:01 PM

We've hit 29.4mpg on a trip using cruise control for 400 miles in our '83SD, set speed was 73mph. In town it gets only about 23-24 though. My car gets about 24-25 city 27 hwy......

t walgamuth · #4 07-20-2005, 11:07 PM

dream of such mileage in my sdl. my 84 300sds did 29 once but the fuel enrichment for boost was not functioning.

bruiser · #5 07-20-2005, 11:34 PM

Quote:

Originally Posted by t walgamuth

i would suspect speedo error. do you have low profile tires?

nope. speedometer is a little bouncy, though. any correlation? i'm at 60mph @ 2600 rpm. normal?

DslBnz · #6 07-20-2005, 11:44 PM

Quote:

Originally Posted by bruiser

nope. speedometer is a little bouncy, though. any correlation? i'm at 60mph @ 2600 rpm. normal?

Sounds normal enough for me.

When you stated "exceptional mileage", before opening this thread I thought I was about to read about an SD acheiving 35 mpg or something.

28 mpg is NOT out of the ordinary for these cars. From my understanding, a good healthy one fetches mid to high 20's with reasonable driving habits.

Heck, if I can get 30 mpg + consistently out of my 4000 lb curb weight SDL, there's no reason the 116 can't get 28. To boot, I never get less than 28 in the summer. But then the SDL is a newer design with taller gearing and better aerodynamics.

(in all fairness however, if my 300SE had another gear, I think I could get mid twenties easily).

boneheaddoctor · #7 07-21-2005, 08:01 AM

Quote:

Originally Posted by bruiser

after two tanks in my '79 sd i'm getting around 28 mpg. granted, these are about 70% highway miles (@70-75mph), but it is even higher than expected. my engine sounds really good, you don't know it's a diesel unless it's idling (and even then it could be mistaken for an old gasser), no smoke at all with the exception of when you really punch it, but this is a few mpg higher than what i expected. i drive fast, but i don't drive hard. what are others getting in their 116 sd's?

i'm going to have the valves adjusted next week (first time i'm leaving it to a professional so i know how it should sound and act when properly adjusted), service records show 30k since the last time, will that increase the mpg even more?

i'm really digging this car thus far. once i get the cruise fixed and a bulb for the tach it'll be mechanically flawless (jinx).

I've never topped 26 mpg and I average more like 24-25 with mine with a nearly 60/40 city highway mix. Over the last 2.5 years.

boneheaddoctor · #8 07-21-2005, 08:02 AM

Quote:

Originally Posted by bruiser

nope. speedometer is a little bouncy, though. any correlation? i'm at 60mph @ 2600 rpm. normal?

I average 3K rpm at 60 mph on mine...and the Diff case is stamped 3.07.....go figure.

t walgamuth · #9 07-21-2005, 09:01 PM

he might have the 2.47 gear... or a bad speedo.

i suggest checking speedo on the interstate. one mile should be covered in one minute at 60 mph.

boneheaddoctor · #10 07-21-2005, 10:09 PM

Quote:

Originally Posted by t walgamuth

he might have the 2.47 gear... or a bad speedo.

i suggest checking speedo on the interstate. one mile should be covered in one minute at 60 mph.

Well I think mine may not actually have 3.07 gears as my W123 turns 3K rpms at a little under 80........one of those two cars clearly does not have the 3.07 gears the case says is in them (both are stamped 3.07).

Brian Carlton · #11 07-21-2005, 10:13 PM

Quote:

Originally Posted by boneheaddoctor

Well I think mine may not actually have 3.07 gears as my W123 turns 3K rpms at a little under 80........one of those two cars clearly does not have the 3.07 gears the case says is in them (both are stamped 3.07).

If the gauges are correct, there is no possibility of a 3.07 in the W123. A 3.07 would be at 3000 rpm with the vehicle at 68 mph..........even less with the stock tires. I'm betting on a 2.47...........but............I can't see how it got in there.

You do the check yet? Take you and your wife about five minutes.

boneheaddoctor · #12 07-21-2005, 10:21 PM

Quote:

Originally Posted by Brian Carlton

If the gauges are correct, there is no possibility of a 3.07 in the W123. A 3.07 would be at 3000 rpm with the vehicle at 68 mph..........even less with the stock tires. I'm betting on a 2.47...........but............I can't see how it got in there.

You do the check yet? Take you and your wife about five minutes.

Nope I never crawled under and did the rotate and count thing...that asphault is damned hot in 95 degree weather....before you factor in the 90% + humidity we have had for weeks here...supposed to be a lot cooler next week however.

baffles me...and the ear relects the tachometer differences too...

but the lower geared W116 gets better milage than the strong running W123 does. Consistantly.

Brian Carlton · #13 07-21-2005, 10:27 PM

Quote:

Originally Posted by boneheaddoctor

but the lower geared W116 gets better milage than the strong running W123 does. Consistantly.

If I had to wager, I'd say the W116 has a better Cd than the W123 does. Might explain some of the fuel economy difference on the highway.

t walgamuth · #14 07-21-2005, 10:37 PM

it is not better drag effeciency. it is gears. imho.

each generation of mbs get slicker and lighter... excepting of course the 140 bodies.

Brian Carlton · #15 07-21-2005, 11:06 PM

Quote:

Originally Posted by t walgamuth

it is not better drag effeciency. it is gears. imho.

Well, you'll have a tough time explaining how a shorter geared W116 gets better fuel economy than a taller geared W123, if you rule out the Cd.

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