28 MPG in a 126
 

As requested, I am going to give some of the details about how I got over 28 MPG on a trip from NC to FLA in a 84 500SEL. We drove about 2000 miles over a 4 day peroid.
Now, to start out, I have heard of 300SDLs geting over 30 mpg so I was thinking maybe I could do it in a gas car. You have to put up with some things (rough ride, poor idle, poor performance at low speed) which I will explain later. Here are the highlights
1. Service with synthitic oil front to rear including P/S, trans,engine,diff.
2. Tires inflated to max cold pressure listed on the tires. (rough ride).
3. Ignition set as high as possible without spark knock using prem fuel.
4. MSD Ignition with plugs gaped at .60 inch.
5. 2.5 inch exhaust front to rear with free flow exhaust. Some of you have heard it and it is not that bad when inside the car.
6. Fuel trim set lean at 2500 RPM. This engine doesn't have a computer.
7. Engine has Euro heads and cams.
8. Now this is the kicker. I advanced the cams 8* at the crank.
9. I would draft big trucks when ever safe.
10. 195*f thurmostate to keep engine hot.
11. 95 % Interstate driving.
12. NO agressive driving. (that was the really hard partof the trip)

What a lot of the above did was make the engine more efficent at 2500-2700 range but hurt it at low rpm. Idle was rough, high speed was powerful, and mid was efficent.
Did I leave the car like this, No Way. I usually get around 20 MPG on a trip but the car runs so smooth I just love it. The above was just to see if it could be done. I proved to myself that you can move the "Sweet Sopt" around for different conditions but you can't have them all without modifications morethan what was done above. Some of these things are still there but some are not.

OK, let it fly, I am ready to defend myself, and answer any questions if anyone has any.
Paul

1. Have you checked your odo against the mile markers?
2. How many gallons of fuel did you use? INclude all addetives.
3. How many miles did you drive?
4. Will you take a polygraph?

It just does not compute.

Tom W

Did you go fishing while in Florida? If so, how large were the fish you caught? How 'bout the ones that got away?

Thank you.

that is the real question.

Tom W

Actually, I was really disputing Paul's claims. I just enjoy being a smartass and I saw my opportunity . . . . .

What do you think IS the best mileage possible in a gas 126?

The best I ever got driving 65 was 19 something. My car was stock. His with the euro heads and so forth if it has the pistons too would do a bit better but would require premium probably negating the advantage.

Actually after thinking it over, I seriously question whether the car would run at all with the "modifications" he lists.

Tom W

Okay. Well, how big do you think the fish might have been ?

In my 380SE I consistently get 16mpg around town and have never done better than 19mpg highway. I don't see how this is possible, even with the more powerful engine. My 560SEL never got better than 20mpg highway.

You raised a good point. Would a larger-displacement engine actually get better fuel economy cruising at highway speeds that a smaller one if all else was the same?

I would assume not, but it's only an assumption.

I don't fish, but if I did I wouldn't be able to find a truck big enough to haul it back home.
Please tell me which modifications would prevent the car from running. I'll have to go scold my 500 and tell it not to do that again because it is impossible.
Paul

420 sel
 

My well tuned 420 sel gets 22mpg at 65 mph , I've checked this several times by putting 10 gallons in when the low fuel light goes on and I can go 220 plus miles on highway trips until the light goes on again . I'm happy with this milage.

Ben

So, Ben, your fish were not as big as Paul's fish, eh?

My last fillup rewarded me 14.5 mpg of cold weather suburban driving. But I have seen 21-22 on long summertime trips.

Well, it's certainly "possible" to get 28 MPG on a car the size/weight/aerodynamics of a 126. My buddy got an actual 28 on his Honda
Odyssey minivan on a 500 mile highway trip once. But, the kicker was, he never drove faster than 60 MPH. And of course, that's a modern DFI computerized engine, with a HIGH OVERDRIVE TRANNY.

Re; the big engine vs small engine question: GM engineers discovered that excellent big-V8 economy can be obtained with the engine in the highest gear possible, turning the lowest rpm possible, with the throttle open wide; just above the point of lugging. This reduces the huge "pumping" losses to overcome the high vacuum in the engine associated with higher rpm and less throttle opening. Obviously, zero intake vacuum results in less pumping loss (theoretically). Also, internal friction and inertia is reduced at these lower RPM's.

So, if you had a big V8 doing 1500 at 75 MPH, and a V6 doing 2200 at 75mph, both at pretty high throttle openings and low vacuum, the V8 might come close, but could never overcome the additional internal friction and inertia; all other things being equal.

Unfortunately, MB never geared the 126 cars for economy. They are all geared for good response and performance, not low-rpm cruising.
They don't even have an overdrive. The 500 SEL would need a differential ratio of less than 1.90 to even get in the MPG ballgame. Imagine trying to launch a 4500 pound 126 in 2nd gear with that differential!

DG

1) I assume you left on a full tank, and filled the tank upon return? (no estimating by the fuel gauge allowed)

2) I assume you kept a log of total miles driven and total gallons dispensed? What are those figures?

jp