Good idea...

My 1978 W116 has a long, one-piece cable with a Bosch cruise servo.

Here are my GPS readings:

INDICATED 30 MPH – ACTUAL 33.5 MPH

INDICATED 40 MPH – ACTUAL 46.5 MPH

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

I opted for the 107 speedo with 160mph readout because it had no fading whatsoever.

Where did you get the photo of the ratio adapter you posted????

I advanced the R107 speedo to match the reading from my 3.07:1 unit...

Attached Thumbnails

 

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Funny,

With the 3.07's the car got better mileage the easier you drove it. Now with the 2.47 the mileage gets better the harder you drive the car.

I've been knocking down 28-32 consistently (over 5 tanks) running 75-85 mph...

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

That's really excellent mileage. This car's a keeper.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Funny,

The car doesn't seem to be affected by the extra aerodynamic drag from the 80-90 mph speeds....

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Engine is just a little more fuel efficient at certain revs. At first I suspected it was just into it's optimal power band. Some serious thought should be given to this. It is almost like the fuel timing is optimum at certain revs. Or the combustion is far better.

Does the running temperature fall off or increase any? Hard to get any form of baseline with a thermostat in the system. Or perhaps feeding a wire back into the cabin from a glow plug to a milli amp meter might show what is happening.

I suspect there might be a peak combustion temperature at the best fuel milage at speed . There should be a fairly narrow band one way or another near the optimum high speed fuel milage. This is just a suspicion by the way.

I have wondered for a long time if increasing the coolant temperature overall would be an asset as it would be fairly safe on these older cast iron engines. Less engine wear is probable as well.

Why I suspect there is or might be something to this is the way my old 1.6 diesel volkswagons seemed to radically increase fuel milage at very high ambient temperatures. Then there is the oil cooler or oil temperature to consider to some degree as well. Hotter oil may present less internal drag.

At 2700-3000 rpm (85-90 mph) the motor is happiest with the 2.47:1 axle and this is where it gets its best economy.

With the 3.07:1 axle, I had to stay at 2500 (55-60 mph) to get the best fuel economy.

Engine runs consistent 15° to 20°F cooler temps at speed with the 2.47:1 even on a 105°F day on the freeway with the A/C on....

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Knocking down 525 miles from 18 gallons....

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

That's 29.1666666666666667 mpg.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Sometimes I wonder if this struggle for fuel economy out of the diesels is worth the effort.

The SE went 487 miles on 20.36 gallons (right to the top of the cap).

The SD's consumption matches yours at lower speeds (62-65). It has the 2.88 with automatic.


I'd rather drive the SE anytime over the SD..........smooth and silent with more torque and a better final drive setup with the new 2.47.

BC,

Agreed...

When the SD was new, it got better mileage than the gassers of the day, but today, I would rather drive a gasser.

My 2001 Mustang GT 4.6 V8 got 28 mpg on my trip last year to Florida with the A/C on....

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Phenomenal..........!!

And do you know what my favorite MBZ of all time is?????

Laugh at me, but I have driven all of the at one time or another and I would take a W201 190E 2.6 over any of them.

They are nimble, easy to park, roomy for their size and the 2.6 is a great performer compared to a 617...FWIW

P.S. #2 is a R107 with M110 and stick shift.

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

But I have to say my W116 has to be one of the most dependable cars ever...

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Now that I have put a few thousand miles on the 2.47:1, I can say that it is a little bit high for the average 617 and other folks who have suggested a 2.88:1 seem to be spot on, IMHO anyways.

While we did not net the 4-5 mpg increase in mileage we had hoped for (during this experiment) we were able to maintain our average fuel economy of 25-28 mpg (and sometimes 30 mpg but not consistently) while increasing the cruise speed from 55-60 to 75-80 mph.

Over the past 20 tankfuls, mileage numbers have been consistent, with calculations altered for the 7.29% speedometer error.

It's a great gear on the highway.

I've recently driven from California to Texas a couple of times and drove the W116 for test purposes and trunk space. On the first leg of that trip I drove non-stop 75-85 (where I could do so safely) with the A/C on and got a full 610 miles on 19.5 gallons, for about 31.2 mpg.

The hills do slow the car down, but it will climb the 'Grapevine' in 4th gear at 70 mph at a little bit off the kickdown switch and I have never had to kick it down into 3rd.

Driving up into Big Bear, California is another story. There are sections where the grade is as steep as 16% in some sections and climbs several thousand feet. That climb involves a lot of downshifts and WOT.

It's a great highway gear to be certain, but as other have posted, I think the 2.88:1 is about as far as one should go.

Hope this helps...

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership