searching for MPG's
 

so I have been experimenting and checking MPG's on the coupe. I have a 60 mile round trip to work so data is slow going. the coupe has a somewhat smaller tank than my d did at around 17-17.5 gallons each fillup. when I first got the car there were some problems and I have worked to get it running smoother without the bigger items like injectors or fuel boost pump or other things I have read help a little. mostly just harder tires at pressure and making sure brakes and such are in good order. with the automatic i was getting around 22-24. i now have a stick so I know the odo is off but im not sure which way and not sure how much. the stick is getting around 26. one thing I have noticed with the stick is that the car's rolling resistance is significantly better. anyone that has let off the gas going backward in the 300D/CD auto knows what I mean. the stick will coast nicely at 35-40 mph for it seems like 1/2 mile loosing very little speed. I have been practicing around the house on the surface streets. florida is very flat so it works well. seems like I can drive around town coasting a little more than half the time. so I just started this in earnest this week. I wondered about whether this is valid or not since I have to bring the engine back up, push a little over the speed limit then let off and coast to below the speed limit cycling on and off. (i dont do this with people following) or is it better just to go slow and let the engine stay at the proper rpm without pushing or accellerating hard, just feathering to maintain speed? anyway, with the 17-17.5 fillups I am now getting around 460 miles a tank. anyone have any feedback on the value of the coast, half-on/half-off method? it seems to take so little to keep the momentum at speed, it seems a waste to use fuel just to keep the engine turning at speed when it is hardly contributing, man I need a 5 speed......

Changing the transmission will not alter the speed/odo reading.

Your practice of coasting in neutral will yield better fuel economy than maintaining a steady speed by carefully feathering in gear. Although it's a small benefit, the engine gets better fuel economy at idle than at 1500 rpm (typical steady state rpm around town in high gear).

The art of coasting to traffic lights in neutral..........and never fully stopping..........will yield some excellent results. Every time you step on the brakes, $$$ goes right out the window.

Not always. Coasting in gear with the engine above idle consumes no (zero) fuel while an engine at idle still burns fuel.

On these older vehicles.........there is nothing to shut down the fuel. So, you get idle fuel quantity at all rpm's. The higher the rpm, the more idle fuel is consumed (more combustion events per unit time).

The governor cuts fuel when the engine is being turned by vehicle momentum above 1000rpm.

That would be an interesting bit of engineering. The governor has some input to whether the vehicle is accelerating or decelerating at 1000 rpm? And, just how would it know that?

Either way, unless you take it out of gear, you will be working against pumping losses while coasting. I think its a sound Idea, but a bit of a pain.

thats taken care of the with manual 4spd, also I have the idle down around 500 rpm so many times I can coast with the clutch in at 500 rpm for 1/4 mile on the highway

How bad is it on the automatic transmission to take it in and out of gear all the time?
On my 1970 220D just about every time I get to a stop light I put it in neutral, is this going to hurt the transmission any at all?
Is it ok to travel at 45 and put it in neutral?
This is my first Automatic.

personally I would never do this with and automatic, too much chance of hitting reverse at speed :eek:

If the ground is flat I would expect little if any upside. Your mass is losing speed while coasting or call it momentum energy. You have to recover it at some point.
In theory if your overall trip speed is reduced there might be a small gain. As one poster mentioned if the injection pump leans out a little at 1000 rpms by design is another consideration. Yes I agree these engines use little fuel at idle when at operating temperatures.
Best mpg gains are probably gotten by keeping the engine tuned up properly from time to time and using synthetic oil. Especially if most trips are very short and local in nature.
Does that thick dino oil ever drag these 240ds down until quite warm in my experience. Never driven another car with as pronounced an effect. That is a lot of fuel milage lost right there.

Going into neutral at any speed is fine.

What they don't like, whatsoever, is going into gear at any speed other than zero. So, going to neutral is not the best thing if you must return to gear at speed.

You can put it in neutral when stopped..........but, why bother? It only causes increased clutch wear when you go back into gear.

Your throwout bearing is not really designed for prolonged engagement with the clutch pedal in as well. It will wear out sooner. This applies to standard transmissions of course. Both my 240ds scream for a five speed on the highway as well. Should have been standard equipment in my opinion.

I get a lot of shaking while stopped in gear, unless I up the rpms.
I need to figure out wait needs to be replaced to stop the shaking.
I have a 1973 220D standard on order. I should have it soon.