45 mpg W124 300D - it's in the math

[sixto]

http://www.fuel-saver.org/Thread-1987-Mercedes-300D-Turbodiesel-40-MPG

Sixto
87 300D

[tbomachines]

Originally Posted by sixto

http://www.fuel-saver.org/Thread-1987-Mercedes-300D-Turbodiesel-40-MPG

Sixto
87 300D

Last post on the page sums up my thoughts exactly. I fail to see how those modifications significantly increase mileage as listed. I am a firm believer in "driving style" modifications for mpgs, but if there is a consistent driving pattern I don't think that guy is fully accurate.

[Shawn T. W.]

Well . . . larger tires, is about the same as lower the rear diff ratio, so IF he runs lots of highway, I could see a gain in mpg.

I agree driving style is probably the biggest factor . . . when I was driving OTR (Over The Road) semi trucks, started back in 92, industry norms were about 5 mpg running 80,000 pounds around the country, the company I worked for offered a $0.01 bonus if we broke 6mpg! I consisantly got the fuel bonus and most of the drivers couldn't because they always had the foot on the floor (we ran 325 hp gov @65 mph) patience, planning ahead, and only idling overnight if it was extreme temps, as we got newer trucks an d more powerful engines (350 hp!) I was always over 7mph, and hit as high as 11 mph one trip! (mostly level running, and I was not in a hurry and kept it at 55 mph with a light load, no idle at night)

I bought a ScanGaugeII for my gmc pu, it plugs into the OBDII port, and gives you instant read outs, it "Teaches You To Drive" effeciently! same as any car with a instant mpg gauge, watch that and you will see you are letting off the go pedal as you go up the hill to keep the mpg high!

Back in the late 80's I had a 81 Caddy Deville w/4100 motor 8cyl, Normally on my way to work in the next town over I had to go over this one hill about 1 mile from where I lived . . . I noticed that if I maintained 50 mph (the speed limit) I would drop to about 11 mpg! One day I had to come back into my home town in the middle of the day, and then go back to work, once the car was warmed up I climbed that same hill going the same direction keeping it at the same speed I got 18 mpg! (warm engine, tranny, wheel bearings . . .)

[Hatterasguy]

Larger tires would reduce fuel economy since you have more rotating mass. Although I don't see how upsizing a bit will affect anything, the change would probably be somethign like 32.659 vs 32.543. But I know on my old SDL going from the stock wheels and tires to the larger ones cost me about 1mpg.


Increasing fuel pressure to the IP won't do much, it doesn't care. The nozzels are still going to get the same pressure. So not sure why the fuel system needed to be hacked.

I'm going to call BS. I think its a light foot, going slow on a nice flat road, and some number fudging.

[awsrock]

Funny you came across this at the same time I did. Did you get it from that 87 wagon on Ebay? The guy selling it said something like "it gets just over 30 now, but it's capable of 40!!!" Yeah, like anyone is going to gain 10 mpg just like that. Ha!
Do you know who started that thread on there?? He is from here..maybe that's why it isn't posted here I won't rat him out though.

[tbomachines]

Originally Posted by awsrock

Funny you came across this at the same time I did. Did you get it from that 87 wagon on Ebay? The guy selling it said something like "it gets just over 30 now, but it's capable of 40!!!" Yeah, like anyone is going to gain 10 mpg just like that. Ha!
Do you know who started that thread on there?? He is from here..maybe that's why it isn't posted here I won't rat him out though.

Yeah if you took out all the seats, gutted it, limited the throttle/fuel delivery and didn't mind taking 5 minutes 0-60, most cars are capable of 40mpg . Maybe you could cut off the roof to lighten it up, then you'd have a custom 87 wagon convertible!

[pawoSD]

Originally Posted by Hatterasguy

Larger tires would reduce fuel economy since you have more rotating mass. Although I don't see how upsizing a bit will affect anything, the change would probably be somethign like 32.659 vs 32.543. But I know on my old SDL going from the stock wheels and tires to the larger ones cost me about 1mpg.


Increasing fuel pressure to the IP won't do much, it doesn't care. The nozzels are still going to get the same pressure. So not sure why the fuel system needed to be hacked.

I'm going to call BS. I think its a light foot, going slow on a nice flat road, and some number fudging.

If you went to physically larger wheels and tires, then your speedometer would have been off by a little bit, as you reduced the final drive ratio. That would account for your "loss" of 1mpg. Once a mass is rotating, it takes very little energy to keep it doing so. Most of the energy a car uses is fighting rolling resistance of the tires, air resistance, and the energy required to keep the physical mass of the car at a given speed....the size of the wheels really has nothing to do with it.

[Hatterasguy]

Yeah I know that.

Same diameter, but with a more weight and width. Wider tires take more effort to turn and will hurt you a bit. Thats why eco cars have skinny little things.

Tire tread makes a difference too. If I put more aggressive off road tires on my truck I'll lose a bit.

[Jeremy5848]

Originally Posted by Shawn T. W.

. . . lI bought a ScanGaugeII for my gmc pu, it plugs into the OBDII port, and gives you instant read outs, it "Teaches You To Drive" effeciently! same as any car with a instant mpg gauge, watch that and you will see you are letting off the go pedal as you go up the hill to keep the mpg high! . . .

I put a ScanGaugeII on my '96 . . . my wife watches the mileage constantly. She says the fuel flow number even decreases if she shifts into neutral at stoplights . . . she can get it down below 0.25 gallon/hour, I don't remember her lowest number.

In any case, driving habits definitely make the biggest difference in fuel economy. I have been watching the "Economy gauge" (gasser vacuum gauge) that I boogered into my W124 diesel (put it in the transmission vacuum line) and definitely see better mileage when I make a point of keeping that gauge as consistently low as possible. Once I have my boost gauge installed, I'll have that to watch as well.

With my sick engine, I doubt I'll ever get over 30 MPG but it will be interesting to see what others do.

Jeremy

[hobbitss]

Originally Posted by Jeremy5848

I put a ScanGaugeII on my '96 . . . my wife watches the mileage constantly. She says the fuel flow number even decreases if she shifts into neutral at stoplights . . . she can get it down below 0.25 gallon/hour, I don't remember her lowest number.

In any case, driving habits definitely make the biggest difference in fuel economy. I have been watching the "Economy gauge" (gasser vacuum gauge) that I boogered into my W124 diesel (put it in the transmission vacuum line) and definitely see better mileage when I make a point of keeping that gauge as consistently low as possible. Once I have my boost gauge installed, I'll have that to watch as well.

With my sick engine, I doubt I'll ever get over 30 MPG but it will be interesting to see what others do.

Jeremy

Big Scangauge II fan and it does help with your driving style...
My E300d at cold idle shows 0.3 gph, warm idle shows 0.2 gph, putting it in neutral at a stop light drops fuel usage to 0.1 gph when warmed up...
Take your foot off the go pedal at highway speeds and the mpg meter shows 9999 as the car slows down...

[t walgamuth]

The taller tires will help your fuel consumption just like changing the rear end ratio and that along with driving fifty five makes me believe your number.

Who can stand to drive fifty five though?

[TheDon]

HHO generator.. haaaaa

Retmil is a member here

[awsrock]

Originally Posted by TheDon

HHO generator.. haaaaa

Retmil is a member here

Yep; I believe he's the guy who lost his 300D in a crash and bought Babymog's. I wonder how it is treating him!

[tbomachines]

I think he's saying bigger wheels and tires = heavier. So it requires more energy to accelerate and decelerate. However, I would think that the tire tread and compound would have much more to do with mpgs since they actually determine how much friction is generated between the car and road.

Now that its mentioned, I think I saw a commercial a few days ago for a tire that was supposed to save 1000 miles worth of gas over the lifetime of the tire (another "stretch" calculation if you ask me)...makes me wonder how well it actually performs, especially in wet and emergency conditions where the contact area/friction really matter.

[oldsinner111]

Well I've gotten 1200 miles on one gal. diesel fuel.