1986 Mercedes 300SDL - Remarkable - Page 2 - PeachParts Mercedes-Benz Forum

MBZ123 · #16 03-19-2013, 02:17 AM

Quote:

Originally Posted by Hit Man X

(very flat, very boring)

You said it Jakk, Goes for Texas as a whole. GAKKK, what a wasteland. I still have nightmares of driving through Abilene at night, ewwwwwww! GOT DOLDRUMS? Can this just be over already? Shoot, El Paso to New Orleans only took a month and a day.

Not so sure anyone would live there if it wasn't for all that Texas Tea.

As for the SDL, just picked up a sweet low miles '86 I'm bringing back to showroom and with my lead foot still managing to get 27 averaged over first three tanks. Gotit just a little over a week ago so no moderate/grammy style cruising numbers to report yet. With $hi##y SoCal fuel, 27mpg at current driving style/experience I may never have the desire or patience to find out.

Yaknow my 123 days might be numbered.

PSYYYYYYYCH!!!!! Whew, another nightmare. It was horrible, there were no 617a's in the garage, or driveway, the yard, backyard, storage, cuz's house, girlfriend's house, parking lot at work...et al. Shudder. Down with this clickity-clack crowd fo-life.

It is still nice driving the girl around in the SDL. She's fallen for the "hey, have I shown you how roomy the back seat is?" trick three times already; don't know when that'll lose its novelty.

Note to self: need to get windows tinted, giggity.

MBZ123

daw_two · #17 03-19-2013, 10:47 AM

Just remember.......

The backseat is big enough to have a party!!!!

Naturally, it helps if you have the 2nd Memory selection on the front seats to be all the way FORWARD.

barry12345 · #18 03-19-2013, 10:55 AM

Then there is the guy who asked the girl he was with if she wanrted to get in the back seat. She replied no way as I really want to be with you.

npretnar · #19 03-19-2013, 01:01 PM

When you removed the fuel cap, did the tank make a sucking noise? A plugged vent would collapse the tank a bit, thus leaving less volume for fill up and therefore skewing mileage towards greater MPG than actual ...

Skid Row Joe · #20 03-19-2013, 03:15 PM

SDLs just don't get 37 mpg. High 20s, maybe 30, but not 37. Low distance / low fills are not indicative of what any car gets, high or low. If they were, my E300TD gets both 18 and 48 mpg. Which of course is impossible.

turbobenz · #21 03-19-2013, 03:52 PM

how much more MPG can be squeezed out of a 603 compared to a 617? Im thinking its only 1-2mpg, which is disappointing.

Skid Row Joe · #22 03-19-2013, 04:17 PM

Quote:

Originally Posted by turbobenz

how much more MPG can be squeezed out of a 603 compared to a 617? Im thinking its only 1-2mpg, which is disappointing.

The answer is; "none," in my experience of logging 337K total miles in mine.

I'm getting basically the identical mpg out of my 603, that I got in my 617 - both turbos.

30 mpg is the 'wall.' Anything over (30 mpg) is basically a rare reading to get.

Stevo · #23 03-19-2013, 04:37 PM

I'm lucky to get 37 MPG with my five speed Euro 240D and its low mileage (125K) and in top shape. I have gotten 35 with my five speed Euro 300TD. Theres no way an SD is going to get near 37mpg. I've gone to 195/75/14s on my 123s and the spedos check out very close now with the GPS.

mach4 · #24 03-19-2013, 04:39 PM

Turns out it's all physics. Here is the fuel consumption map for a 300SD.

I'm only beginning to understand the graph, so for clarity I'm quoting Arcosine from Ecomodder who explains it quite well...

Quote:

The graph is a contour plot of a hill, the top of the hill is the best engine efficiency. The dotted line is trail that goes along the hill. This is where the engine operates on level road. BMEP is how much the engine is loaded, the bottom is no load, top full load at any given RPM. KW is the engine power output, the upper graph. The curved lines going up to the left are engine power isolines. So at 2500 RPM at the dotted line, the car needs 20 KW on level road and uses 300 g/kwh so 300*20 = 6 kg/hr of fuel. Diesel is .8 kg/L so it burns 7.5 L per hour, so that 2 gallons per hour and if the car is going 60 mph at 2500 rpm, that would be 30 mpg.

All the usual suspects change the road load line. Headwind moves it down, tailwind moves it up. Uphill moves it down, downhill moves it up. Under inflated tires moves it down, over inflated tires moves it up. Decreasing coefficient of drag moves it up, increasing coefficient of drag moves it down. Decreasing weight, moves it up, while increasing weight moves it down. Drafting a semi moves it up, while riding the brakes moves it down. Swapping a manual transmission would move it down and downshifting would move it down.

This is a steady-state graph, so during periods of acceleration, the graph doesn't apply since it is not steady-state. Stop and go is deadly on fuel usage, as is idling, and so forth.

Skid Row Joe · #25 03-19-2013, 04:49 PM

Quote:

Originally Posted by Stevo

I'm lucky to get 37 MPG with my five speed Euro 240D and its low mileage (125K) and in top shape. I have gotten 35 with my five speed Euro 300TD. Theres no way an SD is going to get near 37mpg. I've gone to 195/75/14s on my 123s and the spedos check out very close now with the GPS.

All true. Stick MBs are slam dunk mid-30s mpg REAL WORLD producers.

There's NFW a 603 of my vintage produces REAL WORLD 37 mpg, much less 44 mpg as one driver here again claimed last week. In 14 yrs. and 130K miles, my 603 has never cracked 32 mpg. A LOW 32 mpg at that - and that was a one time shot. 30 mpg? Yeah, routine driving highway only, but more accurately 28 mpg tank in, tank out driving. Lower that to 24 mpg summer city driving only, with AC.

My 617 never cracked 32 mpg, and that was in 215K miles, clocking every tank - and most of that was highway driving miles.

RunningTooHot · #26 03-19-2013, 05:06 PM

Cool graph, Mach 4!

Keep in mind that BMEP is not the same as BSFC, although they are interrelated. You can see the little island where the highest efficiency is = 245 grams per KWH.

Shortsguy1 · #27 03-19-2013, 05:09 PM

Quote:

Originally Posted by mach4

All the usual suspects change the road load line. Headwind moves it down, tailwind moves it up. Uphill moves it down, downhill moves it up.

I am a bit short of time right now to really look into this, but at first glance, I would think this is reversed. Road load is the power required on a flat road at a given RPM. So wouldn't it go up (more power required) with a headwind?

Sorry if I am misunderstanding something here.

mach4 · #28 03-19-2013, 05:57 PM

Quote:

Originally Posted by Shortsguy1

I am a bit short of time right now to really look into this, but at first glance, I would think this is reversed. Road load is the power required on a flat road at a given RPM. So wouldn't it go up (more power required) with a headwind?

Sorry if I am misunderstanding something here.

As the road load line goes down, the fuel used goes up.

Shortsguy1 · #29 03-19-2013, 07:05 PM

That top thick black line is the max output on the engine as a function of RPM. The road load is the necessary output of the engine on a flat road to maintain speed. When those intersect at the far right side of the graph, you have the top speed of the car. Using your logic, with a headwind lowering the road load curve, the vehicle would have a higher top speed (as the intersection would shift right to higher rpm and vehicle speed).

Pretty sure that a headwind would raise the road load.

I think you may be getting "fuel use", and "fuel use per power produced" mixed up.

Volker · #30 03-19-2013, 07:31 PM

Quote:

Originally Posted by pawoSD

Drafting semi's is usually grounds for a ticket if a cop spots you doing it....and its also a great way to ruin your: grill, hood paint, headlights, windshield, and so on, with kicked up rocks and dirt from the truck. I stay far back, and keep my car looking nice.

Yeah keep left and stay at 99 mph instead

I am happy to see BSFC noted in chart, and note how eta falls with increased RPM or lower