87 300SDL fuel consumption problem - PeachParts Mercedes-Benz Forum

GregoryV022 · #1 03-20-2009, 05:19 PM

after driving 433 miles, my tank is almost empty. but i think there is something wrong with the fuel gauge because about 375 of those miles were driven on what was indicated to be half a tank of gas.

what im trying to say is my gauge stays above the half tank mark for like a week and a half. but once it hits that halfway mark. its empties in like two days.

is this normal or is there something wrong.

i also feel like i should be getting better than approximatly 22 miles to the gallon

cmbdiesel · #2 03-20-2009, 07:07 PM

Gas gauge may not be accurate, but thats about what you should be expecting for distance per tankful. 17 gallon tank would make that ~25 mpg

GregoryV022 · #3 03-20-2009, 07:09 PM

Quote:

Originally Posted by cmbdiesel

Gas gauge may not be accurate, but thats about what you should be expecting for distance per tankful. 17 gallon tank would make that ~25 mpg

but the 300SDL has a 20.3 gallon tank. the reserve light just came on so i know i have about 2.2 gallons left

GregoryV022 · #4 03-20-2009, 07:12 PM

and if nothing is wrong, how should i tinker with the engine to up the fuel mileage.

also, would a clogged air filter lead to poor mileage. i just replaced it yesterday. i looked inside to find the original or what looked like the original. i don't know the service history as it my grandfathers car but the filter had the 603 part number on it. it looked pretty dirty

Jeremy5848 · #5 03-20-2009, 08:53 PM

A dirty air filter is supposed to be one of the causes of poor fuel economy. Try it with the new filter, see what happens. I can get 22 MPG with my '87 300D Turbo around town if I romp on the pedal a lot but if I take it easy it's more like 25. The SDL is heavier, of course, so acceleration (stop-and-go driving) will be more costly in terms of fuel. At a steady speed of 65 MPH on the highway, though, you should get around 30 MPG.

mplafleur · #6 03-20-2009, 09:34 PM

My owners manual says 23.8 gallons which includes a 3.3 gallon reserve.

Hatterasguy · #7 03-20-2009, 10:31 PM

First if you drained a 23.8 gallon tank in 433 miles that would be 18.19 miles per gallon.

So first you need to get some accurite data.

Get a GPS or use the highway mileage markers, make sure your odometer is correct. Chances are its slow.

Secondly you need to start keeping track of your mileage and averaging it out. One tank is useless data, 12 tanks is good information. To do this you need to fill it up properly, make sure you can always see solid fuel at the neck. You want to do this because different pumps cut out at different times.

Low 20's is all that your going to get out of these big old cars around town.

cmbdiesel · #8 03-21-2009, 07:30 AM

Quote:

Originally Posted by GregoryV022

but the 300SDL has a 20.3 gallon tank. the reserve light just came on so i know i have about 2.2 gallons left

Don't count on having fuel because the reserve light came on.
You'll end up posting to the "Fuel gauge left me stranded again" thread.
Measure your by fuel how much you put in, and it's a good idea to not run the tank dry. There could be untold amounts of sludge algae etc in there.
I typically refuel around 400 miles, and always fill til I see fuel in the neck,
reset the trip odometer(which was verified with mile markers to be accurate) then divide the miles by gallons.
Changing the air and fuel filters (there are two) is always a good idea, and if they are in bad shape, will negatively impact your mileage.
Also check your tire pressure.

sixto · #9 03-21-2009, 06:46 PM

San Carlos isn't quite flat. I'm sure that has plenty to do with 22 mpg.

Have you checked chain stretch and IP timing? Basic things like tire pressure and too much stuff in the trunk?

Sixto
87 300D

triber · #10 03-21-2009, 07:59 PM

I had a stuck brake caliper that was slowing me down, and killing mileage.

GregoryV022 · #11 03-22-2009, 03:09 AM

i need to learn how to write posts, sorry guys.

first of all i have never run the tank dry. and the car has 114K miles on it so im not worried about timing chain stretch or any of the other high mileage problems.

the trunk is empty, ill check the tire PSI tomorrow, but none of the tires look low, and i have a good eye for that i just put in 19.506 gallons at the pump, when i could see diesel at the neck.

i just put in a new filter. i live in the flat parts of San Carlos, white oaks area (for those of you who know where that is).

the brakes are squealing so ill check the calipers.

but im only borrowing this car (for an extended period of time) so i don't want to do to much wrenching on it.

the Odo is accurate to my knowledge.

Jeremy5848 · #12 03-22-2009, 01:13 PM

[QUOTE=GregoryV022;2145591]after driving 433 miles, my tank is almost empty. but i think there is something wrong with the fuel gauge because about 375 of those miles were driven on what was indicated to be half a tank of gas.

what im trying to say is my gauge stays above the half tank mark for like a week and a half. but once it hits that halfway mark. its empties in like two days. . . ./QUOTE]

The sender in the fuel tank may have "diesel crud" on the lower part, causing it to be sticky. Since the car is not yours, you may not want to bother pulling and cleaning the sender but that is what is indicated as a "first try" in such a situation.

Jeremy

JonL · #13 03-22-2009, 02:58 PM

Get some algaecide at a marine store (it isn't legal in street vehicles anymore). Use it according to the directions. It may clear up the sender problem very quickly, it did with mine. I knew I had a problem when I ran out of fuel with 1/8 tank showing one day.

GregoryV022 · #14 03-22-2009, 09:07 PM

would rust on the inside of the fuel cap be a good indicator if water in the tank.

ill try the algaecide think.

JonL · #15 03-22-2009, 09:29 PM

I have a very rusty cap. I have a rusty filler neck. I get some rust in my prefilter.

I don't know where all the water comes from!

I got a new cap, and it started rusting within a couple of months.

I need to do the algaecide thing maybe once every four months or so.