560sl Fuel Consumption issue (Newbie) - PeachParts Mercedes-Benz Forum

Craig87 · #1 02-28-2011, 06:03 PM

I recently just purchased a solid 560sl with 126K on the clock. I had the timing/tensioner/water pump done just to get it out of the way.

This weekend was the first time I got to take it out on the road for any extended period and I discovered I am getting between 7-8mpg. I realize these cars should get around 13-17 combined, so I am clearly out of line.

The 02 sensor was recently replaced as I crawled under the car to confirm what the previous owner said. I replaced the spark plugs with proper Bosch ones. I am not smelling any extra fuel, so I don't think it is running incredibly rich.

I have searched, but I came up empty handed. What is diagnostic checklist I should go through to start narrowing down the culprit here?

tgolden · #2 02-28-2011, 07:23 PM

http://en.wikipedia.org/wiki/Mercedes-Benz_R107_and_C107

I don't have the MB Technical Reference for the 560SL model years, but I do have it for my 1984 280SL and my fuel consumption corresponds to what's indicated in the reference and appears to be the source for the technical information on the link above. In general, manufacturer reported gas consumption mileage is usually on the optimistic side and is not based on real world roads, but test tracks.

The link indicates a 500SL (presumably euro model) estimated fuel consumption at 12.7 mpg. The US model vehicles had more emission controls than the euro models and therefore less mpg.

The 560SL fuel consumption is not indicated on the link. With a larger displacement and late 80's US EPA emission control, the 560SL would likely have significantly less mpg than the euro 500SL.

Considering the age and mileage on the vehicle, I would expect to get about 8 to 9 mpg and you're not that far off. It will likely require professional diagnostic equipment (automotive scope, dynamometer, etc...) to tune the motor for maximum fuel efficiency and get a feel for what the vehicle age and mileage is costing you in gas mileage.

Regards

Craig87 · #3 02-28-2011, 07:29 PM

Well, yikes.

I just assumed it would be a bit better than that based on what people had posted in other threads and my scanning various forums.

Strife · #4 02-28-2011, 08:17 PM

I don't think that is acceptable. I drive the 560 a little harder than the 380, and it gets 14/17, and that's with a first gear start, which hurts gas mileage a little bit.

The 450's had the worst gas mileage due to 3-speed transmissions and less sophisticated fuel management, except perhaps pre-75 models.

rocky raccoon · #5 02-28-2011, 09:23 PM

is unacceptably low. My 560SL is a daily driver with 117k miles and routinely gets 16 - 17 mpg on my local rural country roads. I have seen as high as 20 mpg on a steady speed level road at 60 to 65 mph over a 200 mile trip.

Something is wrong. If the car runs well and does not smoke I would start looking for sensor problems or the ECU itself. I guess it could also be speedometer error.

abiby · #6 02-28-2011, 10:29 PM

Before you get too bent out of shape about the mileage you're getting, I'd recommend checking the mileage over 3-4 fill-ups.

It doesn't sound like you've driven enough to really get an accurate picture of mileage.

LandYaghtLover · #7 03-01-2011, 12:22 AM

My 560 SEL gets about 12 city and 20 highway on a bad day. On a good day I can easily get 13 city and 22 highway.

This was mainly after I adjusted lambda. Mine did not smell especially rich, but adjusting it made an amazing difference in throttle response, power and economy.

I suggest using the fuel reserve light as an "empty tank" indicator. Once that light comes on and stays on for a couple miles reset the trip odometer. Then fill it up with X number of gallons (not $ amounts). Once filled up, do NOT reset the trip again and the gas you put in includes those "negative" miles. (miles past empty). I say this because it works great for me since my fuel gauge is FAR from accurate.

If economy is still low move onto vacuum leaks, etc. Then if that looks good consider adjusting lambda. But its critical the engine has no vac leaks before doing so. If you search tech help, you will find a thread by me about lambda and how to adjust with a simple volt meter (digital, not analog meter). I would bring up the thread, but I have limited abilities on my phone.

Just my 2 cents.

partsman225 · #8 03-01-2011, 06:33 PM

got just back from a road trip all highway 70 to 80 mph fill up right off interstate i got 17.13 mpg. best yet 1991 560 SEL. my old 84 500 sel ruro car. got outstanding mpg's at 23.6 best, i was told that the EHA type fuel systems dump fuel to cool the Cats, decell shut off.

city i dont get much abot 10

check you tire pressure if you getting poor mpg's