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Old 05-07-2011, 03:43 PM   #1
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Cummins 8.3.

I have a 2000 Monaco Diplomat with an ISC 8.3 315 HP Cummins. Since purchase it has used one pint of oil per thousand miles. After this years spring service the consumtion has increased to a quart per thousand. Performance seems the same. Can the turbocharger cause oil consumption problems? As always THANKS for any info.

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Old 05-07-2011, 10:06 PM   #2
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Originally Posted by jdecastro View Post
I have a 2000 Monaco Diplomat with an ISC 8.3 315 HP Cummins. Since purchase it has used one pint of oil per thousand miles. After this years spring service the consumtion has increased to a quart per thousand. Performance seems the same. Can the turbocharger cause oil consumption problems? As always THANKS for any info.
More likely the loss is due to the crankcase vent tube. They are notorious for not separating oil mist out of the blowby gases. The tube is behind the oil filter but does not extend down too far. Look for wet oil on the bottom of the engine and toward the back of the coach. There is an Open Crankcase Ventilation kit available from Fleetguard and Racor. Or you put the end of the tube into a catch container. You will still lose the oil. It will just not be as messy. From personal experience, the addition of an OCV provides mixed results. The location of the original outlet breather hose is low on the engine and is subject to much more liquid oil making separation much more difficult. Previous model C8.3 had the tube coming out of the valve cover. Works much better to add the OCV kits.

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Old 05-08-2011, 12:50 PM   #3
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You don't mention the mileage on your coach or the oil that you are using. Has been my very unscientific experience over the years with many different types of vehicles that, for some reason, some oils seem to get "used" faster than others. Example....Penzoil versus Quaker State. Always used more Penz than Q/S between changes. Don't know why. And Motorcraft oil never went anywhere except where it was supposed to (bearings, rings, valvetrain, etc.). Since you just noticed this after the last service, did you change oil brand or viscosity recently? Are you sure the filter was changed as well? Is the filter sealing properly? Have you noticed any new oil leaks anywhere? If the usage increased abruptly, it is likely something else other than the engine that has caused it. In other words, what has changed, and was it sudden or gradual? 1 quart per thousand miles on a higher-mileage vehicle would not be considered unusual by some folks. 1 quart versus 1 pint all of a sudden would be considered unusual by most folks. Just MO...please let us know what you find out. Thanks!
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Old 05-08-2011, 01:30 PM   #4
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I had the same engine as you in a 2000 motorhome too. From the beginning it used one quart of oil every 1500 miles and I always topped it up the the full mark. After about 40,000 miles I stopped topping it off and it never used another drop. When I changed the oil I left it a quart or two low and it remained at that level until the next change 15,000 later.
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Old 05-08-2011, 06:03 PM   #5
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Hi jdecastro,
Gut feel says Norm4015 has the answer. I had the same problem and found the same solution. My ISC is very persnickety as to where it wants the oil level to be. Mine will sit right at the ad oil level on the dip stick and no oil is burned. Put any more in and it will be gone in 1K miles. I do my own oil changes. Now it is filled to two quarts less than full. No more oil burning.
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Old 05-08-2011, 08:09 PM   #6
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My 8.3C behaves exactly the same as Gary's regarding oil consumption.
Jim & Kate
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Canada, eh?
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Old 05-09-2011, 03:23 PM   #7
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Norm has the answer, run a Qt low and I think it will stop the loss.
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Old 05-09-2011, 06:13 PM   #8
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Yes, old 8.3L with 85,000 miles. Run 2 quarts low. Zero oil consumption.

The dipstick may be miscalibrated.

Oil analysis was very reassuring to the condition of engine and oil.
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Old 05-11-2011, 08:43 AM   #9
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Cummins 8.3

Thanks for all the replies. The engine has 52500 miles on it. I will talk to the service facility about cvhange of oil brands. I also will be a little less diligent about adding oil. I had an airplane once that would throw out the top quart of oil. Again thanks.
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Old 05-11-2011, 07:35 PM   #10
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You might try shell rotella T 15-40, or Chevron Delo 400 15-40 both good quality HD diesel oils. Mine will get rid of about 3 qts in between changes 65K miles on the clock. Also your ISC makes it's peak power around 17-1850 RPM (check your engine owners manual) if you keep it turning about there 58-62 mph in 5th or 67-70 in 6th you will find it will run cooler, shift less, and much more comfortable to drive. There is such a thing as lugging a diesel engine among other things it will cause high oil consumption, ISC's are not high torque rise engines so you have to keep em turning to keep em happy, its not going to hurt it, so stand on it and let er breathe. And to answer your question a bad turbo seal will cause oil consumption, but with the low mileage on your coach its unlikely you have turbo issues

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