Fuel Economy: Not Pleasantly Surprised - Page 3 - PeachParts Mercedes-Benz Forum

Hatterasguy · #31 01-12-2008, 01:06 AM

Yeah, true. What kills my mileage is that its all around town. 0-40-0, even on I95.

So the mileage is lower, and I burn through brake pads in 30k miles.

whunter · #32 01-12-2008, 01:34 AM

Quote:

Originally Posted by Craig

Actually the force due to wind resistance increases with the square of velocity and the power required to overcome that wind resistance increases with the cube of velocity.

Now the question is???

I have a 1985 300SD getting 28 MPG at 65 MPH.

What MPG would I get at 115 MPH???

Yes, it will go that fast.

PaulH · #33 01-12-2008, 02:00 AM

300SDL, 140k, owned since new. Suburban, urban combo mileage around Wash DC area - - 25 mpg; on a long trip @ about 70-75 --25 mpg. With the old diesel fuel I got 26 mpg! It was estimated (At several diesel engine meetings that I went to in 2006 when I was still in the trucking industry.) that the ultra low sulfur fuel would cause a loss of about 3% in fuel economy. One to two people in the car, 34 lbs press. in tires. Also get about 30K on front brake pads, 60K on the front rotors. The service manager at the dealership when I got the car told me to expect about 20-25K on the front pads. And, since new, uses about 3/4 qt. of oil between dino oil changes. Syn. oil would probably give me about an extra 1 mpg I guess.

300SDog · #34 01-12-2008, 02:59 AM

Quote:

Originally Posted by Skid Row Joe

The mpg increase was not just a lot to write home about, Brian, but it was there. A tad less than a 10% increase over 65 mph.

Yep, I've seen this myself driving cross country recently with my 300SD where lugging the engine at 60 actually produced *worst* fuel mileage than it got operating at 70mph.

But I guess theoretical engineers are too busy considering wind drag coefficients and weird velocity vectors to consider the FACT that diesel engine efficiency with optimal power produced through most efficient combustion largely relies on sustaining/maintaining engine speeds within rpm power band range.

Meanwhile here's something else to consider: Driving coast to coast 3,000 miles at 60mph takes 50 hrs. And driving 70mph takes approx 43 hrs. Does anybody honestly believe 60mph for 50 hrs will burn less fuel than 43 hrs driving at 70 especially as optimal engine efficiency occurs at engine speeds that more closely match 70mph?

(edit: and makin a habbit of lugging yer engine fouls piston crowns and combustion chambers makin it into a slug that delivers neither economy nor performance, as everybody knows

pawoSD · #35 01-12-2008, 03:08 AM

Over Christmas we had pretty bad weather, so I made a couple 70 mile commutes going about 45-55mph (varying, but never over 55) and on that tank I jumped up to 26.4mpg vs my normal 24ish. But I am able to get 23-24 going 75-80mph...which is fine by me. I'd much rather be going 75 than 45, thats for sure.

Skid Row Joe · #36 01-12-2008, 03:51 AM

Quote:

Originally Posted by 300SDog

Yep, I've seen this myself driving cross country recently with my 300SD where lugging the engine at 60 actually produced *worst* fuel mileage than it got operating at 70mph.

But I guess theoretical engineers are too busy considering wind drag coefficients and weird velocity vectors to consider the FACT that diesel engine efficiency with optimal power produced through most efficient combustion largely relies on sustaining/maintaining engine speeds within rpm power band range.

Meanwhile here's something else to consider: Driving coast to coast 3,000 miles at 60mph takes 50 hrs. And driving 70mph takes approx 43 hrs. Does anybody honestly believe 60mph for 50 hrs will burn less fuel than 43 hrs driving at 70 especially as optimal engine efficiency occurs at engine speeds that more closely match 70mph?

(edit: and makin a habbit of lugging yer engine fouls piston crowns and combustion chambers makin it into a slug that delivers neither economy nor performance, as everybody knows

Absolutely correct, 300SDog...... The E300TD was built to deliver it's optimum MPG at RPM sweet spots.......my mileage at speed proves it. The E300TD begins stretching it's legs between 70-75 mph, in my mileage tests.

Real world applications trump the classroom boys every time. They cannot think-outside-their-box of formulae. They're not trained to think for themselves, by applying practical hands-on experience, thusly, it cannot be, in their limited minds. Books, are their only source of knowledge.

Ara T. · #37 01-12-2008, 04:24 AM

Quote:

Originally Posted by 300SDog

Yep, I've seen this myself driving cross country recently with my 300SD where lugging the engine at 60 actually produced *worst* fuel mileage than it got operating at 70mph.

But I guess theoretical engineers are too busy considering wind drag coefficients and weird velocity vectors to consider the FACT that diesel engine efficiency with optimal power produced through most efficient combustion largely relies on sustaining/maintaining engine speeds within rpm power band range.

Meanwhile here's something else to consider: Driving coast to coast 3,000 miles at 60mph takes 50 hrs. And driving 70mph takes approx 43 hrs. Does anybody honestly believe 60mph for 50 hrs will burn less fuel than 43 hrs driving at 70 especially as optimal engine efficiency occurs at engine speeds that more closely match 70mph?

(edit: and makin a habbit of lugging yer engine fouls piston crowns and combustion chambers makin it into a slug that delivers neither economy nor performance, as everybody knows

How is going 60 mph in 4th gear lugging your engine? My 300D drove beautifully around town shifting at 2000 RPM. Plenty of torque to spare at that speed.

#38 01-12-2008, 05:08 AM

An engine is lugging only when its incapable of accelerating the vehicle when the throttle is pressed.

Ara T. · #39 01-12-2008, 07:21 AM

And you'll hear that nasty tapping sound of bearings being starved of oil, which is what I hear when my friend's mom drives his Ford Ranger

Something that AT equipped cars won't experience, only improperly operated stick shifts.

tobybul · #40 01-12-2008, 08:04 AM

Ok, might as well sneak in here.....

I have always scratched my head when I see claims of 30+ mpg on SD's or D's. I'd like to know the conditions when this occurs...... speed? tail winds? no wind? head winds? driving habit? .... hype?

best I've done is 22.... I think that if one wants to attain 30+ mpg on an older diesel and drive "realistically" at the same time, I would suggest getting a VW Rabbit....

But then again, as I always say, 22 +- is not bad for a big car.....

Brian Carlton · #41 01-12-2008, 08:25 AM

Quote:

Originally Posted by 300SDog

Yep, I've seen this myself driving cross country recently with my 300SD where lugging the engine at 60 actually produced *worst* fuel mileage than it got operating at 70mph.

But I guess theoretical engineers are too busy considering wind drag coefficients and weird velocity vectors to consider the FACT that diesel engine efficiency with optimal power produced through most efficient combustion largely relies on sustaining/maintaining engine speeds within rpm power band range.

.........more factually incorrect statements. There is no possibility that a 300SD gets better fuel economy at 70 mph when compared to the fuel economy that it gets at 60 mph.

.........and, I've got 75K miles of data to prove the theory.

Brian Carlton · #42 01-12-2008, 08:28 AM

Quote:

Originally Posted by Skid Row Joe

Absolutely correct, 300SDog...... The E300TD was built to deliver it's optimum MPG at RPM sweet spots.......my mileage at speed proves it. The E300TD begins stretching it's legs between 70-75 mph, in my mileage tests.

.........more factually incorrect statements. A diesel engine doesn't have a "sweet spot". It burns fuel based upon rpm and load. If you increase the rpm..........it burns more fuel due to increased friction within the engine. If you increase the load (wind resistance), it burns more fuel to compensate.

Bama1 · #43 01-12-2008, 09:24 AM

Quote:

Originally Posted by Douglas.Sherida

...240TD manual 5 speed
urban: 9.5L/100km
at 90km/h: 6.3L/100km
at 120km/h: 8.7L/100km
...

Did you mean 240D? I have never actually seen any 5-speed except for a retrofit transplant from the 190D. What year(s) and what country were they available in the w123 and where can I get one?

motor on

jbach36 · #44 01-12-2008, 09:44 AM

Can't be that much to fix, right? I can tell you that Mapquest gives VERy wrong directions sometimes, recently took me about 3 exits south of where I needed to be, during rush hour traffic, only to go right, then back back north to where I needed to be. So who knows about their mileage.

How hard to fix the odometer? I thought it was just a cable.

jeff

nhdoc · #45 01-12-2008, 09:49 AM

I'll chime in here too. My '98 E300 which I routinely drove up and down the northeast corridor between NH and NJ will usually get around 30-32 MPG at my typical cruising speed of 70-80 MPH, typically these are warm-weather trips so summer blend fuels are used.

One time I tried an experiment and filled the tank before I left NH and drove the whole way with the cruise set at 65 MPH, the legal limit over most of the trip. I was passed almost constantly the whole trip as the average speed along this route is 70 MPH. On my test trip I made it all the way to NJ and back on one tank and got a record 36 MPG, the highest I have ever gotten on any trip. So, yes, if you have patience and don't mine seeing the scowls of passing motorists you will get better mileage at 65 MPG than at 70-80, period. It's empirical evidence that proves out the theory that I already knew was true.

Crackpots feel free to flame away...I won't waste my time responding to you anyway.