And here I thought I was increasing my gas mileage... - PeachParts Mercedes-Benz Forum

cirrusman · #1 06-04-2011, 06:39 PM

I just installed a set of new injector nozzles in my '83 300SD in hopes of fixing my constantly deteriorating mileage. When I got the car I was getting 35 MPG, and slowly deteriorated until I averaged 22. Now, right after changing the nozzles (the car sounds great though) I'm getting 18 MPG?! What the... I don't know where did I make the wrong turn here, but I'd appreciate any suggestions.

Daman858 · #2 06-04-2011, 06:42 PM

It takes a number of miles for the new injectors to set in, provided that, of course, they have been pressure tested and balanced. Mine took about 500 miles before the car was running perfectly.

kerry · #3 06-04-2011, 06:54 PM

There's no way in the world a 617 will return 35mpg in an SD. 22-25mpg is standard on a 617 in a car.

tyl604 · #4 06-04-2011, 07:30 PM

Kerry is right. I am the original owner of an 81 300SD and your mileage makes no sense. The best I have ever gotten is mid 20's on the expressway. You should be getting an average of 20 maybe 21 in a combo of city and expressway driving. Or are you calculating kilometers?

sixto · #5 06-04-2011, 07:31 PM

You're probably getting the same cr@p California pumps dispensed as D2 for years. Our Diesel Suburban gets 19mpg locally, 22mpg in Oregon.

Sixto
87 300D

cirrusman · #6 06-04-2011, 07:35 PM

Quote:

Originally Posted by tyl604

Kerry is right. I am the original owner of an 81 300SD and your mileage makes no sense. The best I have ever gotten is mid 20's on the expressway. You should be getting an average of 20 maybe 21 in a combo of city and expressway driving. Or are you calculating kilometers?

Nope, miles. What I do is to divide the miles I've traveled by the gallons I pump in. I do this every time I pump diesel in the car. 3 years ago, I got numbers around 35 or so (Once, on a long trip to a small town in N. UT I got 37), slowly going down every time I went to the gas station. As of lately I've been getting a constant 21-23. Today I got 18...

tyl604 · #7 06-04-2011, 07:39 PM

Sorry, something wrong with your calculations. Maybe your odometer is off due to wrong size tires or something. But you are just not getting that kind of mileage. 21-23 is about right. 18 if you are doing more city driving makes sense too. Down to earth again. Were you experimenting with hypermiling at that time?

sixto · #8 06-04-2011, 07:46 PM

Are you measuring each fill-up or adding to previous fill-ups?

Sixto
87 300D

Orv · #9 06-04-2011, 08:01 PM

Check your odometer for accuracy. Mine likes to "take a break" every once in a while, which can appear to really ding fuel economy. VDO odometers tend to develop cracked gears that cause them to stop intermittently, or sometimes permanently.

That said, I've never gotten better than high 20s in my OM617-powered 300TD.

tbomachines · #10 06-04-2011, 09:34 PM

Quote:

Originally Posted by kerry

There's no way in the world a 617 will return 35mpg in an SD. 22-25mpg is standard on a 617 in a car.

Why are people so quick to condemn high mileage? Just because you can't get 30+ mpg in that car doesn't mean it is completely impossible. I've gotten 33mpg in my 300SD (twice) and it typically sits right around 30 on the highway simply because I don't speed, don't use AC, follow trucks (not dangerously though) and don't have a lead foot.

This isn't limited to the diesel section either, I've been told I was lying about my 300E's 30+ mpg too until I posted photos of the gas pumps and GPS readouts. The point about the odometer being broken is a good one though, these have a tendency to strip the gears. A good GPS readout is necessary every couple months at least, if you are concerned about the odometer accuracy.

tangofox007 · #11 06-04-2011, 09:46 PM

Quote:

Originally Posted by tbomachines

Why are people so quick to condemn high mileage?

Because they know what they are talking about.

Quote:

Originally Posted by tbomachines

Just because you can't get 30+ mpg in that car doesn't mean it is completely impossible.

You might be able to drive down hill with a tail wind some of the time...

vstech · #12 06-04-2011, 11:29 PM

Quote:

Originally Posted by tangofox007

Because they know what they are talking about.

You might be able to drive down hill with a tail wind some of the time...

nahh.
a SD in great tune with perfect brakes, and driven on level ground, kept under 63mph with a good wax on the metal, and a good alignment with high tire pressure, and no floored starts can achieve 30mpg... MAYBE slightly above, I don't see 35 in the cards without some creative fillups... but IF all highway low speed driving behind trucks for wind breaking, I suppose it's within the realm of possibility... but I really doubt it.
the 18 is likely due to your brakes dragging, and the tire pressure being low, along with your odometer slipping a tad, and position of the tank bubble when filling the tank.
remember it's a 21gallon tank... how much are you filling it each time? how low are you? to be really sure of your mileage, you need to save all gallons purchased over a REALLY long time, and add up the totals and divide the gallons over like 10,000 miles to know what you are averaging.
likely it's in the 24-27 range if you are REALLY careful, or in the 19-24 range if you're not...
you could be driving with a worn timing chain, and a weak alda also...

1980sd · #13 06-05-2011, 12:01 AM

I've driven a lot of miles in my '80 300sd even though I'm pretty new to it.

Picked it up near Miami and drove it home to Mid. Ga, I travel for work and have taken it out a few times but it seems to break...

Anyway, about 50/50 interstate, a lot of state hwy, very little city driving.

My numbers have been between 20mpg Running 80-90 for stretches but mostly high 60's

To 28mpg with running 55-60. (Favorable winds)

I try to fuel up at the same temp, check mileage with GPS, etc. I fill it with the same volume from the same tic mark on the gauge each time...

This has been over 2200 miles.

It is what it is

vstech · #14 06-05-2011, 12:21 AM

and the 80 is the old non aerodynamic 116 body... the 126 has more refinements...

cirrusman · #15 06-05-2011, 11:04 AM

Thank you all kindly gents for your input. There might possibly be a flaw in my system of measuring mileage... I fill up every Saturday and reset my odometer to 0; the next Saturday I fill up again, see how many gallons I pump into the tank, and divide that number by the miles my odometer shows. Back in the day, my results were giving me 30-35 each Saturday. Then, slowly, started dropping. One Saturday my result would be 29. Next it was 28.5. next it would be 27. next 29 again, then 28, 26, 29, 26, 24, then 22, and then it stayed pretty steadily at 21-23 for the next year. So one day I started longing for those days when I got those nice 30-35 numbers. I knew that my injectors were a mess, the engine sounded really loud and then it started knocking, so I decided to get new nozzles. Since I can't pop test them, I took my injectors to this diesel place, where they installed the nozzles, deep cleaned and polished them, but the lady in the front desk could not get the pop test results for me. Oh well, I thought, and proceeded to install the injectors in the car. Besides a small leak on injector #5, which I sealed with a blue sealant that came with the nozzles, I noticed nothing amiss, and now the car runs so smooth and silently I can hardly believe it. I was feeling optimistic about my mileage too, what with that glorious purring sound my engine is making now, it should go up to the 30s at it used to! Disappointment. I went, filled up, counted, divided by and got a really disappointing 18, which I get for the first time too.
Your comments are valid too, my odometer might be slipping here and there, I'll have to check it. My tires are brand new and checked at 40 PSI. My alignment has gone to the dogs and that might be something too; I have to replace some parts in the front undercarriage that make clunk noises every time I hit a bump...
Thank you gentlemen for your insight!