Getting the best MPG from your SL - PeachParts Mercedes-Benz Forum

UT_Tech · #1 06-11-2008, 10:21 PM

We’ve noticed a huge variation of MPG in our customer’s cars and we’ve decided to do something about it. There’s now an online tool to help maximize your MPG. The 107 chassis has an undeserved reputation for poor fuel economy. Some of our customers report 15 MPG or worse on the highway, but this can be fixed. There are a few simple things you can do which should increase the fuel economy to mid-20s on the hwy. The purpose of the online tool is to address the power consumption part of the MPG problem. Engine efficiency will be addressed separately.

To get the most MPG, we need to measure the car, not the driver. For this reason we’re proposing to measure the actual power required to move the car down the road at a steady speed of 65 mph so driving habits do not affect this measurement.

Fuel is burned in the engine to make power. The power produced by the engine is used to move the car down the road. To maximize fuel economy, both the production and use of engine power have to be measured accurately.

The on-line power used calculator & instructions on how to use it are found here:

http://unwiredtools.com/utcoastdown.asp

rcounts · #2 06-12-2008, 12:24 AM

Can't seem to get it to work. Clicking on the CALCULATE button just gives an "Error on Page" message...

Strife · #3 06-12-2008, 01:27 AM

This is an interesting formula. I seem to recall reading that the 80's Geo Metro took only 5 horsepower to push at 55MPH, which is still pretty impressive.

The Yugo, OTOH, took two people to push at 2 MPH due to the use of sleeve bearings in the axles

UT_Tech · #4 06-12-2008, 01:49 AM

If you get an error on the page, just close your browser and try it again. The page has been getting a lot of hits.

I can admit to a youthful indiscretion. Many years ago as a teenager I owned a Fiat 850. It was a terrible car but I did manage to measure the engine load at 60MPH. As I recall it was only 6.5hp.

Setting the toe on my SLC saved 3hp.

JimFreeh · #5 06-12-2008, 06:54 AM

My SLs get their best mileage on my car trailer.

Jim

neds380sl · #6 06-12-2008, 08:31 AM

My 380SL has been getting 22-23 when I drove it (fast!) from Boston to Virginia and back. No complaints here!

UT_Tech · #7 06-12-2008, 10:59 AM

23MPG driving fast is good. I rented a PT cruiser and it did about 19mpg on the same stretch to Phoenix as my 380SLC did about 24MPG.

If you're getting a lot worse than this on a 450SL it's not because the engine is larger. SLs should get mid 20's on the hwy. The WUR enrichment is more agressive on 450SL than a 380SL but that can be changed if you want better MPG.

tecqboy · #8 06-12-2008, 11:27 AM

What happened to the thread started by the fellow who was putting acetone in his gas for better mileage? It seems he was getting some noticable improvement in mpg. I lost track of his link.

UT_Tech · #9 06-12-2008, 11:49 AM

I didn't see the thread but it's a terrible idea. The plastics used in the 70s vintage fuel systems are soluble in acetone. Don't do it unless you're looking for an excuse to buy a new injectors.

tecqboy · #10 06-12-2008, 01:53 PM

You can read about acetone here... http://www.pureenergysystems.com/news/2005/03/17/6900069_Acetone/

I don't buy into it myself. The engineer side of me says modern cars already effectively burn gasoline near 100% to achieve low emissions. And like you, I wouldn't put acetone near rubber or plastic auto parts. But there was a fellow here on the forum who was running his own experiment; and now I can't find it.

UT_Tech · #11 06-12-2008, 02:14 PM

It's always tempting to re-invent the wheel. The basics always work, a given amount of energy goes in, another amount comes out. Simple. There are simple and inexpensive tweaks to maximize efficiency in the engine. There are simple and straightforward ways to minimize the load on the engine.

Fuel additives, magnetic enhancers, vortex swirlies, and good luck charms haven't contributed much to the state of the art. If someone invents some new thermodynamics please let me know.

Q45Denver · #12 06-19-2008, 02:21 PM

I don't think a couple ounces of acetone in 10 gallons will do much harm. At least not as much as 10% ethanol does.

riorust · #13 06-19-2008, 02:35 PM

Quote:

Originally Posted by tecqboy

What happened to the thread started by the fellow who was putting acetone in his gas for better mileage? It seems he was getting some noticable improvement in mpg. I lost track of his link.

Is this it ??
http://pages.prodigy.net/jforgione/MB_ace.html

UT_Tech · #14 06-19-2008, 03:01 PM

I agree, a few ounces won't hurt. I can't imagine how it would affect the mileage either.

BTW, A 300CD owner in San Diego found this thread and contacted me. He was getting poor mileage (18-20MPG) and tried the coast-down test. The test showed excessive drag which was traced to a suspension problem. The steady-state MPG calculation jumped from 21MPG to 30MPG. As soon as he passes on his after-repair mileage I'll post the results here.

Bottom line, measuring the drag performance really works.

askay · #15 06-26-2008, 04:14 PM

Interesting. I have an R129 rather than a 107 (96 SL500). I did this, and got an MPG reading in the mid-to high 20s. But I'm only getting high teens gas mileage. So how do I proceed from here to identify problems and fix them? I'm semi-knowledgeable about cars and relatively new to this Benz. Are there diagnostics to be done? A protocol for checking systems out? I can list what I know of the condition of my car, and would be happy to provide specifics, but mainly I'm looking for an understanding of how I go about getting the answer or answers. Thanks!

Alan
Berkeley