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  #46  
Old 07-11-2014, 01:00 PM
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Originally Posted by Skid Row Joe View Post
Thanks for the additional information regards the thermostat, Jim. My CDI does run very cool for quite a time on the coolant temperature gauge. When the DC fans run, it's only for a brief time I've noticed. I haven't driven the car but a couple thousand miles in the 13 months I've owned it. (2,700 mi) most very short rips like two to five miles from home on errands.
I agree that the thermostat makes a huge difference. Mine stuck open in winter, yielded about 17mpg on the computer with the temp reaching no more than 50-60C. The shaft inside the thermostat bent, not allowing it to close. New thermostat jumped right back to 32+ mpg.
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  #47  
Old 07-11-2014, 01:51 PM
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Originally Posted by TimFreeh View Post
double

Want to see 44-46 MPG from a CDI? I'm almost 100% sure anyone can if they drive it a constant 50MPH on a flat road with no headwinds on a nice day with the tires inflated to 40PSI and the A/C off. I'm also betting you could get 38 MPG out of an OM603/W124 combo under the same conditions.

Nobody here ever stated you could get 46MPG on a daily basis under normal driving circumstances. The data you reported from fuelly sounds about right for someone that is driving primarily in a suburban environment - and its what I'd expect to get if I was driving in such an environment.

The expanding hot diesel thing is certainly a real issue, however that is only an issue if your re-filling from a tank that is fairly full - if you're checking mileage after the reserve light has come on and you've got 1.5 gallons of 'hot' fuel in a 21.5 gallon tank I don't see it as a significant factor.
Yeah but who drives at a "constant 50MPH on a flat road with no headwinds on a nice day with the tires inflated to 40PSI and the A/C off. " .

Very few so that's almost never.
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  #48  
Old 07-11-2014, 02:23 PM
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Originally Posted by JimFreeh View Post
Joe, Under those conditions it would not be unusual for me to see a cumulative rating around 30.

When my wife uses the car for errands, it's under these same severe conditions, stop and go, low speed, short runs, etc., and I note a significant lowering of the average mpg on the trip computer.

When you can drive a CDI in the following manner:

1. Constant speed.
2. Significant duration.
3. Fairly flat terrain.
4. Drive as Jackie Stewart recommends.
5. Car is in peak tune.

You can indeed get way, way above the EPA range.

Absent one or more of the above, and you will not achieve peak efficiency. It's not normal for me to get all 5 going for me at once. But, boy, when I do, it's pretty impressive.

Jim
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Originally Posted by Maxbumpo View Post
Joe,

That is pretty severe service in my opinion as well, because you may not be getting the engine oil up to temperature. You may have water building up in your oil pan. Water + dissolved contaminants can produce acid, which will eat the bearings and the cylinder walls and other things. That damage will take many years to cause engine failure, but it will eventually.

A new thermostat may allow the engine to get up to operating temperature more quickly, but I'd recommend that at least once or twice a month, you drive for 30 minutes or so in order to drive the accumulated water out of the engine oil (and the transmission oil, power steering fluid, differential...). You may want to consider changing your engine oil annually, despite the low mileage, or at least send in a few samples for lab analysis to see what's going on.

My '95 E300 takes about 10 minutes of driving before the engine coolant temperature is normal. My '87 300TD only takes about 5 minutes of driving. My understanding is that the engine and transmission oils don't reach operating temperature until about 15 minutes of additional driving after the coolant reaches normal temperature.
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Originally Posted by spark3542 View Post
I agree that the thermostat makes a huge difference. Mine stuck open in winter, yielded about 17mpg on the computer with the temp reaching no more than 50-60C. The shaft inside the thermostat bent, not allowing it to close. New thermostat jumped right back to 32+ mpg.
Thank you all here for the additional instruction, and specific information about the danger in driving too few of miles always in my vehicles. I've got to find a way to drive longer times and distances in the CDI, going forward.

Now, to learn how to change out my CDI's thermostat myself, without breaking anything on it, using the proper materials and methods too?
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  #49  
Old 07-11-2014, 02:24 PM
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Originally Posted by funola View Post
Yeah but who drives at a "constant 50MPH on a flat road with no headwinds on a nice day with the tires inflated to 40PSI and the A/C off. " .

Very few so that's almost never.
Well if you're universe is NYC I'd totally agree. Here on the Delmarva peninsula I do about 90% of my driving under the exact conditions cited.

I do agree though, for many people the 46MPG potential won't ever be realized however lower 40's on a long road trip with speed in the 65-70 MPH range is easily obtainable.
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  #50  
Old 07-11-2014, 03:19 PM
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Quote:
Originally Posted by TimFreeh View Post
double

Want to see 44-46 MPG from a CDI? I'm almost 100% sure anyone can if they drive it a constant 50MPH on a flat road with no headwinds on a nice day with the tires inflated to 40PSI and the A/C off. I'm also betting you could get 38 MPG out of an OM603/W124 combo under the same conditions.

Nobody here ever stated you could get 46MPG on a daily basis under normal driving circumstances. The data you reported from fuelly sounds about right for someone that is driving primarily in a suburban environment - and its what I'd expect to get if I was driving in such an environment.

The expanding hot diesel thing is certainly a real issue, however that is only an issue if your re-filling from a tank that is fairly full - if you're checking mileage after the reserve light has come on and you've got 1.5 gallons of 'hot' fuel in a 21.5 gallon tank I don't see it as a significant factor.

It's insignificant.

The standard reference temp for fuel looks to be 60 degrees F. If you use 100 degrees F as your ratio, the difference is 1.84%

Now, since you are filling up a tank that's much less than full, the real affect is about 5% of the above number. That would be less than 0.46%

Now let's assume the ambient temp wasn't 100 degrees F (Hint: It wasn't.). How about halfway between 60 and 100? So now we're looking at an a possible effect of less than 1/4%.

BTW, my father had a Chem E. PhD. I'm well aware of the temperature bias WRT when to fill a vehicle. Dad always encouraged us to fill up in the morning. That habit, is one of the many legacies he left.

Jim
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  #51  
Old 07-24-2014, 07:53 PM
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Originally Posted by Skid Row Joe View Post
The foreign country 2.7 liter versions of the I6 CDI sold overseas are likely plenty fast enough, and perhaps more fuel efficient than our 3.2 liter U.S. lightening quick and fast version.
Not sure why MBUSA chose to go with the 3.2L 6cyl, other then for performance. It can deliver on the highway, but with any town or stop & go driving the mileage numbers really take a hit.

The 2.2 I4 or 2.7 I5 would have been a better choice for economy, while still offering reasonable performance.
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Last edited by MB_FanAddict; 07-26-2014 at 03:27 AM.
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  #52  
Old 04-04-2015, 03:15 PM
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Not sure why MBUSA chose to go with the 3.2L 6cyl, other then for performance. It can deliver on the highway, but with any town or stop & go driving the mileage numbers really take a hit.

The 2.2 I4 or 2.7 I5 would have been a better choice for economy, while still offering reasonable performance.
I viewed a YouTube of a CDI in the UK with the 2.7 that lit-em-up from a dead stop. I gave it a try once by cancelling the TracControl. Yup, it lights 'em up loud 'n proud.
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