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Old 04-26-2015, 03:39 PM   #1
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Sprinter MB diesel engine RPM At highway speed

Any one notice RPM's at 65-70mpn on highway?
I suspect my trans is not reaching highest gear for highway.
2600 RPM at 65. Fuel economy down to 17 mpg. I did not make
a mental note of RPM's before now. Thanks for any info.
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Old 04-26-2015, 05:08 PM   #2
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Yes you have a problem. 2600 is way above the peak power point for a diesel and thus it shows it is not in the right gear for that speed. I would assume closer to 1900 would be correct. It almost looks like you are 2 gears down.

Now I do not have a MB diesel but driver several others.
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Old 04-26-2015, 05:54 PM   #3
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The torque curve for the 3.0-liter v6 turbodiesel is pretty much flat at 400 lb-ft all the way from 1600 rpm to 2400 rpm, so at 2600 rpm you're not far off from your peak torque.

The torque and horsepower curves here are not from a Sprinter, but it's the same engineÖ


I see from your data that you are in the Lafayette area. Were you running with your air conditioner on when you noticed the lower fuel economy? The load from an A/C compressor causes the engine to work harder to deliver the same performance. And as any pilot knows, engine performance also has a lot to do with air density, humidity, and temperature. It may just be that with the warmer temps and high humidity we've had lately, your engine had to work just a bit harder than it did a few months ago when the weather was cooler and dryer.
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Old 04-26-2015, 06:41 PM   #4
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My dodge 6.7 ,at 65 is about 1550 rpm.....
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Old 04-26-2015, 06:53 PM   #5
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Although I am not familiar with the Sprinter, I found that the sweet spot towing with my 2008 Jeep GC with the Mercedes Diesel was at 62 to 65 mph and about 2200 to 2600 rpm. 14 to 17 mpg. The motor currently has 220,000 miles on it and is running beautifully, although we had to do some oil seal replacements on it recently. This Jeep towed a 25 ' and a 30' Airstream and is currently out to pasture being used as a daily driver hauling kids around. My current Jeep with the VM Motori diesel has a way more jam and gets better fuel economy. Jim


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Old 04-26-2015, 07:00 PM   #6
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Quote:
Originally Posted by tjdonahoe View Post
My dodge 6.7 ,at 65 is about 1550 rpm.....

My guess is you also get excellent fuel economy and you may be able to cox 750,000 ? miles out of it without huge expenses. You have an extremely desirable motor. Jim


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Old 04-26-2015, 07:09 PM   #7
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Your RPM is normal for the 5 speed transmission and 3.0 liter Blue Tec diesel. Mine runs at the same RPM at that speed, and I do around 20,000 open road highway miles a year, along with about an additional 10K of in town driving.

The MB diesels with the 5 speed run a bit higher than other diesels to maintain the torque. My VW 2.0 diesel with a 6 speed runs at about 1800 RPM at that speed. The new 7 speed on the '15 Sprinters runs at a lower RPM also.

At the speed limited 82MPH, I rev at just under 3000.

My '11 Sprinter 2500 has 112,000 miles on it and is still running well. About to head to Oregon for the summer work schedule and will be adding another 10,000 miles by the time I get back to FL.......most of it highway.
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Old 04-26-2015, 07:42 PM   #8
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I think you should add an "electrically-driven compressor".
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Old 04-26-2015, 07:44 PM   #9
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... As Lewster indicated your RPMs are normal. If you want more than 17 MPG you will have to drive slower. At a steady 60 mph I get 19 MPG. Remember these Interstates are heavy, running at about 10,000 lbs.

Here is the engine data on the Sprinter V-6 diesels.

Enjoy,
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Old 04-26-2015, 08:20 PM   #10
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The Sprinter is slightly more aerodynamic than a shoe box on wheels. But every 5 mph incremental increase over 55 will probably take 10% off the miles per gallon.

I see about 2050 rpm at 65 in my 2007 Mercedes ML320 CDI with 7 speed and the 3.0L V6 diesel without DEF. I have about 127,500 miles on the vehicle now, so it is finally loosening up a little..... The difference in the power ratings lies in the chip installed as the basic engine design has remained fairly static since it was introduced. The ML class for the USA got the 3.0L V6 in the 2007 model year.

My 6.7L Cummins peak torque is at 1650 rpm in 6th gear which is exactly 65 mph on both the GPS and the speed-o-meter. That same rpm in 5th is around 55 mph which works for us, too.
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Old 04-27-2015, 11:45 PM   #11
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I haven't driven by sprinter on the highway for about a month but those numbers seem normal. Even with the elevated RPM's I experience anywhere from 17 to 24 mpg depending on speed, wind and other variables. Headwinds and crosswinds have a definite negative effect on mileage especially at higher volosities.
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Old 04-27-2015, 11:49 PM   #12
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Normal engine rpm and gas mileage

[QUOTE=John Millner;1613686]I haven't driven my sprinter on the highway for about a month but those numbers seem normal. Even with the elevated RPM's I experience anywhere from 17 to 24 mpg depending on speed, wind and other variables. Headwinds and crosswinds have a definite negative effect on mileage especially at higher volosities. Check again under different conditions and I think you see an increase in mileage. Don't forget to check your air pressure in your tires too.
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Old 04-28-2015, 01:39 PM   #13
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Thanks to all for info. I am not as concerned with mpg at 17 for last short trip. I convinced myself that the rpm's were off. I had auto shifting problems week before in N. Ga mountains esp after manual shifting up and down steep driveway and subdivision hills. 12 to 17 degree inclines/declines. I feel better that nothing has changed now. I get 18 to 20 mpg at highway speed for 11hr trip to and from Ga. home back to Lafayette. I just had never noticed highway rpm's before. I am very familiar with Cat diesels also chevy duramax diesel. Both run at much lower rpm's
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Old 04-28-2015, 04:30 PM   #14
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And both are a lot bigger than 3.0L.
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