I have found with this car, with all its torque, it will pull most hills with out downshifting. If a vehicle I am driving will pull a hill with out downshifting I will leave it in cruise. When I got the 36mpg I was running in Western N.Y state and it is pretty hilly. I also will accelerate going down hills with the cruise on and then let the cruise take over going up the next hill.

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1998 E300Turbodiesel
1980 300d

Ready- Ronnie

Cruise controls waste fuel in two main ways. First, they use as much throttle as required to maintain speed up hills. Doing so wastes fuel - it's more efficient the maintain throttle up hills and lose a little speed. Second, cruise controls effectively "pump" the throttle, on-and-off, in an attempt to maintain an exact, pre-set speed. Again, this is an inefficient driving style. A human can easily beat cruise in MPG, if they know how to drive.

On a slight thread hijacking tangent, I'm a bit underwhelmed with the om606 turbo. The best MPG my 98 ever delivered was ~33MPG, I never once hit the rated 34. This past weekend I did a small road trip in my 210 wagon (w/m112 V6). On the way home it returned 30.5MPG, cruising 65-70MPH on the highway. A few years ago I posted a back-of-the-envelope calculation that showed no cost of ownership benefit of the diesel. It returns a bit better fuel economy - just a bit on the highway. But it needs glow plugs more frequently than the V6 needs spark plugs. That expense eats up the fuel economy savings. And the V6 seems more reliable - it has a flaky harmonic balancer vs. flaky glow plugs, leaky fuel lines, and the risk of breaking a glow plug off in the head on the diesel. I voted with my dollars, sold the diesel, and went gasser...

- JimY

Sorry, but I've got to disagree with you.

The cruise is generally the most efficient way to operate the vehicle if you want to achieve a specific time over a set distance.

If you allow the vehicle to decrease speed on the hill, you must add fuel coming off the hill to accelerate it. Your only benefit from the decrease in speed is due to the reduced wind resistance on the body.

Cruise controls do not "pump" the throttle. They apply a gradual increase to the throttle and anticipate the speed of the vehicle based upon the acceleration. A driver is poorly equipped to do this and cannot achieve anywhere near the smooth operation of a cruise control.

I'm quite sure that a cruise control will get you to your destination faster with less fuel consumption than if you drove the vehicle manually.

First, cruise control is to help relieve fatigue on long trips. A driver should be able to maintain a set speed at least as precisely as the CC. I qualified my comment that this doesn't apply in flatlander country. In hills or mountains, CC will do precisely the wrong thing if max mpg's are the only measurement criteria. That IS the subject of the topic. Going down the hill, the CC will let completely off the throttle in an attempt to maintain speed which is it's only measurement criteria. As your car passes the low point in the road, the CC will compensate and frequently overcompensate for the rapidly decreasing speed by flooring the throttle if necessary. OTOH, if a device with independent thinking capabilities (preferably a driver) sees the upcoming hill, he will allow the car to garner additional speed which the vehicle will then use to help propel it over the top. In the extreme, your speed may go over 100mph and may bleed down below the speed limit as you bleed off the excess energy. I have driven this way when traffic and speed enforcement was light. Try it. Huge gains in MPG's. On my motorcycle, I went from routinely getting around 40 to getting a little over 60 mpg's. If a human were trying to duplicate a CC, all he must do is focus on the speedometer and maintain a steady speed no matter what his brain tells him is ahead. OTOH, if he covered the speedometer and focused exclusively on a miles per gallon instrument, he would drive as I stated.

So let me restate the fact. Cruise controls are HUGE wasters of energy except in laser flat terrain and that's what the discussion was about.

This may not be relevant, but I have found that it matters a great deal to the MPG calculation whether the fuel tank is properly filled or not. Because diesel foams, the pump shuts off well before the tank is full. I have found that I can add almost another gallon to the fuel tank by waiting for the foam to de-foam. It takes more time but then I know the tank is full.

It really should not matter about whether you squeeze every last drop into the tank every time you fill it because you should not be basing your fuel economy on one tank anyway, and over the course of several tanks the "error" tends to balance out. The key would be to be consistent if you want consistent readings out of each tank, but overall average MPGs over several thousand miles would be the same within a reasonable margin even if you were not.

If you fill up at a particularly slow pump one day and the fuel doesn't foam as much you get a little more into that tank so the mileage for that tank will be a little higher, then the next time you might get a little less and therefore the mileage for that tank might be a little lower. Over time it averages out. I suppose if you really want to be scientific about it then yes, the best way to measure it would be to make certain the tank is absolutely full every time, but frankly, over the course of many tanks just filling it until the pump clicks off would be fine. You're not going to see that much difference either way.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Does this mean you were at 21 psi?? That is a sidewall failure waiting to happen at 80mph!

Really? Don't know about you but between shutoff and seeing fuel at the mouth of the tank, I get about 3 gal and some change.

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01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow

Not any more. It is now set at max inflate pressure.

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01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow

Whew!

As for fuel mileage in my 99 E300TD, I have a book that I have logged every fillup since new and have some numbers for you. My car now has 71,972 miles, and I have purchased 2,891.314 gallons of diesel fuel in 169 individual fillups since I rolled the car off the lot new in Oct 1999 with a total of 8 miles showing on the odometer. Up to date this equals the following averages:

24.892488 MPG, 425.87 miles per tank

Highest individual MPG for one fillup: 38.5 MPG (steady 60 mph)

Lowest individual MPG for one fillup: 22.7 MPG (winter)

Highest # miles on one tankful: 779.4 miles -Yardley, PA. to Midway, GA. (fuel gauge was a hair above dead-dry. Fillup at Midway was 21.89 Gallons- in a tank with a 21.1 stated capacity!)

I believe the 18" AMG staggered wheels and Michelin Pilot Sport tires I currently run reduce my MPG by about 1.5 MPG on average versus the stock wheels and tires..I also always keep the tires pumped up to 40 PSI.

I ALWAYS fill to 2.5 gallons beyond initial "automatic fuel shutoff" and could probably squeeze another .3 gal. in if I waited another several minutes. (I already piss off the truckers waiting behind me at the pump as it usually takes close to 5 minutes for a "true fillup" of an average fillup of about 18 gal per fillup!)

I would classify my driving style as moderately aggressive, and I'm not afraid to "enthusiastically" step on the accelerator when the circumstance requires...this happens to be OFTEN!

J.G.

...to report that with we in NH now have warmer weather, apparently summer blended fuel and lower prices (yay - just over the price of regular gas here at $2.11/Gal) I can report that my average MPGs are now very close to 30, getting 29.5 on my most recent tank in the 1998 E300 DT. This is dramatically better than the 25-26 I was getting in winter and have noticed a steady improvement as the thermometer clicks up. Basically my driving is a mix of highway and city, about 50/50. I'm hoping that this next tank breaks the 30 MPG barrier

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Hi there, nhdoc.

I just netted 27 mpg in my SDL and I paid 2.229. When I tap the pedal now, the car leaps. The fuel is definitely better.

Watch out in Seabrook NH, on Rt 1. They used to have an Arab running the Getty near the delta of 107(he created competition), but he's no longer there and prices are no lower than 2.299. Absolute theft!

BTW, what did you pay specifically?

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)

I just paid $2.11/Gal at Shell (in Nashua) which I prefer but saw one station at $2.08 yesterday which was no-name fuel that I wouldn't use. I have found that Shell and the one time I used Shell "premium" diesel I got better performance and better mileage than using Mobil which is my normal station. In fact, when I used Shell Premium in the 240D I recently drove up from Florida it was the one tank I actually got 32 MPG from! The average on that trip was only 27 or so. None of my local NH stations seem to sell Shell Premium however. I wonder if it is regional?

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

I've never seen Shell "Premium" diesels. Not specifically as in, labled back to back "regular" diesel vs "premium" diesel. The Shell's around here usually sell "Premium" diesel and nothing else.
Lucky, me.

Heck, in NH they don't even rate the cetane levels for ignition quality. It's a toss as to whether you fill up clean, or dirty.

2.119 a tank. Wow, looking forward to < 2.00 a gallon.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)