Second fill 30mpg

[Varn]

I finally got to my second fill on my Mercedes 300D and got 30 mpg.

Not bad for a 3700 pound vintage tank.

[arcosine]

Does it have a lock up torque converter?

[Varn]

No just a 4 speed auto. Once it gets to about 40 it shifts into 4th and just builds rpm from there. Turning 25-2600 at 60.

Funny thing is that 60 is about the bottom of the powerband in 4th. You have to let off to get it to cruise at 65, otherwise it just keeps accelerating, I think the turbo is coming on. It is going to take some experience to figure where it cruises most economical.

[arcosine]

This a fuel map for Mercedes 300 sd:

Looks like its overpowered or geared too low for maximum mpg. Deactivating 2 injectors would put it at 37 mpg.

[Varn]

I would agree Tony that it feels geared too low. It has a 2.88 gear ratio and 195/70x14 tires. Top gear is 1:1 with a torque converter that slips a couple hundred rpm.

Somehow I don't see me blocking off two diesel cylinders.

Help me understanding the graph, what does the dashed line sloped up to the right and the solid line at the top mean. The graph is for the heavier SD rather than my D Does that make a difference?

Originally Posted by arcosine

This a fuel map for Mercedes 300 sd:

Looks like its overpowered or geared too low for maximum mpg. Deactivating 2 injectors would put it at 37 mpg.

[arcosine]

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. There's a 190D for sale on CL in st louis I saw.

[Varn]

Tony, I have thought about the graph. So the dashed line reflects the car with standard gearing and aero drag. If the gearing were made taller for less RPM/road speed then it (the dashed line) would be pushed to the left and closer to the peak efficiency?

Looking careful at the graph, if I was to drop 300 rpm 2500 to 2200 I might move from 300g/kwh to 280 g/kwh?

[arcosine]

Yes, it would follow a constant power isoline at 20 kw.

[Johnmichelsr]

Originally Posted by Varn

I finally got to my second fill on my Mercedes 300D and got 30 mpg.

Not bad for a 3700 pound vintage tank.

it would be nice if you share some pics now

[Varn]

Now! eh
Click on Benszilla for a profile and some stats









Been busy putting taking out some years of neglect.
The egr valve was leaking like a sieve, now it has 9 psi of boost making it run like a 4.9 liter NA diesel engine
Valves were all so tight from lack of service.
I don't look for economy numbers to come up till spring.

Originally Posted by Johnmichelsr

it would be nice if you share some pics now