AWESOME Fuel Mileage!!! - PeachParts Mercedes-Benz Forum

deerefanatic · #1 09-04-2007, 09:02 PM

Well guys, we took my SD and my Grandma's Pacifica up north for the Labor Day weekend.... I tabulated my mpg and the scores are in. These are GPS verified for distance..... I filled the tank of the car up just to the point of overflow dribbles each time.... Bounced the back end of the car to make sure no bubbles...... Filled on level (or very close to level) pads.... Car loaded with Three adults (175, 165, 150) plus about 125 lbs of luggage......

First Fill, mostly level ground.. Very easy driving at a near constant 61mph with some towns and a little passing..... 158 miles - - - - 4.58 gals back to full........ 34.49 MPG!!!!

Second Fill, VERY hilly driving with lots of acceleration and passing, in altitudes averaging 900ft..... 235 miles - - - - 8.636 gals to full - 27.23 mpg

Third Fill, coming home. Same terrain as First fill, but with more passing and aggressive driving behavior.... 161 miles - - - - 5.86 gals to full - - 27.47 mpg.

maybe those eBay sellers aren't so far off after all!

bgkast · #2 09-04-2007, 09:41 PM

The 27s seem more reasonable. The 30-something could have been a fluke, or an error in measurement of fuel volume (not all pumps cut off at the same point). Not too shabby though…

DslBnz · #3 09-04-2007, 10:25 PM

Highest I've ever achieved with my 300SDL's is somewhere between 32 - 33 mpg.

I believe it. Especially if the environment was as described, flat and at a constant 61 mph.

Of course optimal fuel efficiency is achieved at approximately 80 km/h (50 mph) according to the European fuel consumption charts included in the owner's manuals. It is possible, according to Mercedes-Benz, that a 300SE gasser can get better than 30 mpg at that speed, but only 21 mpg at 75 mph.

I should post a scan.

Tymbrymi · #4 09-04-2007, 10:48 PM

Quote:

Originally Posted by bgkast

The 27s seem more reasonable. The 30-something could have been a fluke, or an error in measurement of fuel volume (not all pumps cut off at the same point). Not too shabby though…

The only time I've gotten 30+ MPG was a complete fluke. I filled up at the worlds slowest fuel pump (as in it took 30 mins to fill up 1/3 of a tank... seriously). Probably ended up with like 26 gallons in my 21 gallon tank (went to the filler neck with **no** foam). IIRC, I got over 700 miles on that tank. Went from Gallup, NM to the other side of Oklahoma City

. I think it was something like 36MPG at 70MPH because when I filled up at the next stop it filled to the normal amount.

I second the 27s as being reasonable. On that same trip with the cruise at 60 I got 28. With the cruise set at 70 it was around 26.

All these numbers are for my '79 SD. I get 28-29MPG at 80-85 in my 2.5T

2.5Turbo · #5 09-05-2007, 01:12 AM

Quote:

Originally Posted by Tymbrymi

I get 28-29MPG at 80-85 in my 2.5T

Gotta love that 2.65 rear end...cruisin' at 75-80 at 3000-3200rpm feels perfect. I get about the same numbers at high speeds. Normally I average around 30. If I keep it down to 60-65, I get into the low 30's. Highest ever was 36. May have been a fluke, but it was at a Flying J where you'd expect the pumps to be in good working condition...so maybe it was real, they were all highway miles at 70mph or so...

Biglex · #6 09-05-2007, 02:39 AM

Quote:

Originally Posted by 2.5Turbo

Gotta love that 2.65 rear end...cruisin' at 75-80 at 3000-3200rpm feels perfect. I get about the same numbers at high speeds. Normally I average around 30. If I keep it down to 60-65, I get into the low 30's. Highest ever was 36. May have been a fluke, but it was at a Flying J where you'd expect the pumps to be in good working condition...so maybe it was real, they were all highway miles at 70mph or so...

That is for sure about the rear ends in these cars. Best I got was 34mpg, and that was doing alot of 75-80 mpg driving from wv to sc. From my experience, these cars arent too quick off the line, but they sure are comfortable at 80.

nhdoc · #7 09-05-2007, 12:31 PM

As others have said you can't tell anything from a single tank and the way you measured it you are most likely to amplify any error in filling it. The reason is you can easily have a ±0.5 gallon difference on filling the tank up depending on lots of factors including but not limited to: the angle the car is at parked at the pump, the temperature of the fuel remaining in the tank, the speed at which the fuel is pumped (creating foam or not) and for that matter the fuel itself and how foamy it is.

As careful as you think you are you you can NEVER fill a fuel tank to precisely the same level every time. If the car is sloped ever-so-slightly away from the pump it will take more fuel than if it is sloped towards it.

So, by measuring after using only a few gallons your error is amplified because a 0.5 gallon error out of 5 gallons would be 10% or about ±3 MPG while that same 0.5 gallon error on a full 20 gallon tank would only be 2.5% or about ±0.75 MPG. The most accurate readings therefore would be taken after burning as much fuel as possible from the tank between fillups and then averaging several of them.

If you did it this way you'd probably discover that the first trip was an anamoly and you'd really be getting around 27-28 MPG on 100% highway driving...and that's about typical for these models.

SD Blue · #8 09-05-2007, 12:52 PM

Great mileage! It sure shows how driving habits and conditions seem to affect mileage more than just the car itself.

BTW, if it comes to splitting hairs.....the only way to get extremely accurate readings is by weighing the fuel. But the only time I would go to that extreme is if someone is paying me to do a scientific study.

deerefanatic · #9 09-05-2007, 10:08 PM

Quote:

Originally Posted by bgkast

The 27s seem more reasonable. The 30-something could have been a fluke, or an error in measurement of fuel volume (not all pumps cut off at the same point). Not too shabby though…

Ok, more details.

filled car up at the Shell in Centreville MI. Level concrete. Filled up to bottom of filler neck, NO FOAM.

1's top off, Marathon Station, Sears MI. Pump 11, Level Concrete. NO FOAM

2nd top off, same as above.

3rd top off, Marathon Station, Centreville MI. Level Concrete, filled to bottom of neck hole, NO FOAM

That is as precise as you can get folks......

Tymbrymi · #10 09-05-2007, 10:20 PM

Quote:

Originally Posted by deerefanatic

Ok, more details.

filled car up at the Shell in Centreville MI. Level concrete. Filled up to bottom of filler neck, NO FOAM.

1's top off, Marathon Station, Sears MI. Pump 11, Level Concrete. NO FOAM

2nd top off, same as above.

3rd top off, Marathon Station, Centreville MI. Level Concrete, filled to bottom of neck hole, NO FOAM

That is as precise as you can get folks......

Approx. how many gallons did you put in each time? As nhdoc mentioned that does contribute to the amount of error in the reading (although I do think you can get close to decent mileage off of one tank). FWIW, I usually drive my cars to less than 1/4 tank before I fill-up. Almost always less than 1/2 tank.

deerefanatic · #11 09-05-2007, 10:40 PM

I got the receipts from the car for the 2'nd and 3rd fills.... It was 4.588 gals for the first fill.....

2nd was 235 miles with 8.636 gals

3rd was 161 miles with 5.860 gals.

tarbe · #12 09-05-2007, 10:46 PM

I wouldn't bother trying to get economy readings on 4 and 5 gallon runs.

As was stated earlier, the % error will kill you on such small fills.

Wait until you can pump at least 15 gallons to minimize the effect of normal variations in pumping etc.

Tim

Biglex · #13 09-06-2007, 03:49 AM

Quote:

Originally Posted by SD Blue

Great mileage! It sure shows how driving habits and conditions seem to affect mileage more than just the car itself.

BTW, if it comes to splitting hairs.....the only way to get extremely accurate readings is by weighing the fuel. But the only time I would go to that extreme is if someone is paying me to do a scientific study.

amen to that. that is the BEST way to get the most accurate measurement of fuel. On race day, we have to go by weight since we dont have fuel gauges. We do it backwards though, by measuring the fuel left in the can.

Basically you can do as much testing as you want. You may not be perfect on your measurements, but you can do it so that you arent far off enough to totally hose your equations. I would be willing to go by the original figures on this post given the facts presented.

pawoSD · #14 09-06-2007, 08:32 AM

I always go long (14-17 gallons to fill it up) periods....well, thats usually only about 4-5 days....but still.

Best I get is about 24-25mpg....I got 24.34 last night when I filled up. Most of my driving is city or 80-85 freeway, so its not bad at all. My dad's car gets slightly better but it has better fuel injectors too.

I don't think 34 is possible in a 300SD unless it was all at 45mph, with no stops, for an entire tank....and downhill most of the way. Best either of our cars has EVER gotten was 30.7 and 31.3 when driving about 300 miles @ 55mph with no stops.

When filling up with only 4.48 gallons even slightly unlevel ground could easily skew the numbers. If the car was on a very gentle slope towards the passenger side you could easily lose up to 1.5-2 gallons of capacity....bringing the mileage down to 26 even if off by 1.5 gallons. You need to run the tank down 17-18 gallons at a time.

deerefanatic · #15 09-06-2007, 09:24 AM

I usually do, but wanted to see what difference there was in different terrain.

I doubt it's do to concrete levelness. As you'll see, I filled #1 & #2 at the same station, same pump, same side of pump, facing the same direction with the same passengers and the same load.......