diagnosing poor fuel economy: 22mpg - Page 3 - PeachParts Mercedes-Benz Forum

RallyRebel · #31 08-22-2010, 08:21 PM

Crikey people, y'all draggin' boat chain?

My '81 turbo 300D consistently gets 34MPG hiway and about 30 mixed, and the '81 240D manual is doing about the same and the injectors are crap (about to be rebuilt). Heck, the '80 300SD does 30MPG easy so while not exceptional (I was VERY spoiled for a while with an '06 Jetta TDI, 56MPG best hiway) I've got an '86 M1028 CUCV that beats the mileages y'all posted. Maybe check your tire pressures?

JB3 · #32 08-22-2010, 09:25 PM

Quote:

Originally Posted by RallyRebel

Crikey people, y'all draggin' boat chain?

My '81 turbo 300D consistently gets 34MPG hiway

How are you getting 5-10 mpg better than anyone else on average? Have you made any changes to the vehicle to get that?

35 is the best I have been able to do in a 240 with an overdrive, and I freely admit that was with a tailwind. Usually I get 31-33 highway with that drivetrain. Its been pretty consistent with factory figures-

for 123.123 (240D) with OM616.912
.................................city 56mph 75 mph
240D with 4 spd manual: 24.7 / 32.6 / 23.7
240D with 5 spd manual: 24.7 / 37.3 / 27.0
240D with automatic:.... 24.7 / 30.5 / 22.2

What is your usual highway cruising speed?

t walgamuth · #33 08-22-2010, 09:49 PM

I'd check your odometer and the diameter of your tires. Smallish tires will make your odo read wrongly and inflate your mileage calculations. I always check my odometer against the highway mile markers.

NY300SD · #34 08-23-2010, 12:25 PM

That ladder must have an incredible amount of drag. Just think of the wind whistling through all those steps. You've got to get a reading without anything on top to see what your car is actually capable of.

RallyRebel · #35 08-23-2010, 09:31 PM

The 240D I got recently and flew out to MS to drive back to FL and got about 32 with crappy filters and WVO partially in tank. PO had bought to run on WVO for a year before selling, I got it because it was manual everything and I wanted an economical commuter after selling the '06 Jetta TDI. After new filters, new tires in stock size and some basic maintenance I managed the 34MPG. Hoping to get better after rebuilding the injectors with new nozzles, the ones in there now look like crap and spray about the same. I'm not lead-footing nor am I babying it, the only plus I could possibly have is Florida's flat sea-level roads.

Fattyman · #36 08-23-2010, 11:17 PM

Quote:

Originally Posted by zeke

x8 or however many wagon owners have already chimed in...

35 is a pipe dream even for a 4-sp NA 240D.

I measured 52 MPG with my 81 240D 4 speed once upon a time.
All highway miles measured with the odometer and a GPS. Fuel replaced with a measuring cup. I checked my math twice to be sure because I couldn't believe it myself.

t walgamuth · #37 08-24-2010, 06:01 AM

Quote:

Originally Posted by Fattyman

I measured 52 MPG with my 81 240D 4 speed once upon a time.
All highway miles measured with the odometer and a GPS. Fuel replaced with a measuring cup. I checked my math twice to be sure because I couldn't believe it myself.

I think you had better measure again unless you were doing 32 miles per hour.

JB3 · #38 08-24-2010, 07:57 AM

Quote:

Originally Posted by t walgamuth

I think you had better measure again unless you were doing 32 miles per hour.

agreed, whats more likely? you get 20mpg better fuel economy on the highway than every other 240 owner? or the math is off.

Even at 32 miles an hour, you would not get 52mpg. Maybe if you towed the car idling.

JB3 · #39 08-24-2010, 08:00 AM

Quote:

Originally Posted by RallyRebel

The 240D I got recently and flew out to MS to drive back to FL and got about 32 with crappy filters and WVO partially in tank. PO had bought to run on WVO for a year before selling, I got it because it was manual everything and I wanted an economical commuter after selling the '06 Jetta TDI. After new filters, new tires in stock size and some basic maintenance I managed the 34MPG. Hoping to get better after rebuilding the injectors with new nozzles, the ones in there now look like crap and spray about the same. I'm not lead-footing nor am I babying it, the only plus I could possibly have is Florida's flat sea-level roads.

On a 240, 34mpg makes sense, but originally you said you got 34mpg in an 81 300D turbo, which is pretty amazing for the 5cyl in the 123 chassis. Did you get that fuel economy in both?

RallyRebel · #40 08-24-2010, 08:15 PM

Quote:

Originally Posted by dropnosky

On a 240, 34mpg makes sense, but originally you said you got 34mpg in an 81 300D turbo, which is pretty amazing for the 5cyl in the 123 chassis. Did you get that fuel economy in both?

Yeah, my 300D turbo gets regularly 32MPG and sometimes when it's cool and the planets align 34MPG which is why I was very disappointed with that same economy out of the 240D. I now have a regular 140 miles commute while back in school getting re-edumacated so figured the 240D should be doing around 40MPG give or take. Coulda sworn I'd seen many claim the same for the manual cars.

t walgamuth · #41 08-24-2010, 10:28 PM

If you're getting 32 to 34 with a turbo I would suspect an inaccurate odo or undersized tires. 27 to 29 is very very good for one of those, except in high altitudes where they seem to do better.

mplafleur · #42 08-25-2010, 01:27 AM

I think anything above 25 mpg on a turbo is a gift.

I could get 30 mpg on my non-turbo '75 300D if I kept the speeds down to 55 or so. Yes, it was that long ago.

RallyRebel · #43 08-25-2010, 06:59 AM

Tires are 195/70-14 BFG Traction T/A on bundts all three cars, although I run my pressure around 45 psi. Sorry guys, not trying to brag just was stunned when reading the original posts in this thread. I've always been under the impression my mileages with in the norm for these cars as I've always seen exceptional economy from diesels. I've even got a beater '98 Ford E-350 PowerStroke with 240K miles that was given to us and I've managed to get to 17MPG in mixed driving hoping to improve with more maintenance.