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Old 07-10-2021, 02:58 PM   #1
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Exclamation Excessive Blow-by Cummins 5.9 24V

I'm having an issue with blow-by. I've always had a little oil that would come out the vent tube, made a Catch can years ago and all was well.

Fast forward to this year. We have been out only 2 times this year and each time I have been getting crazy amounts of blow by that will fill up my bottle in about 100 or so miles.

on our last trip (390miles on the return) home we went through 4 gallons of oil, all blown out the slobber tube. Engine doesn't feel low on power so I'm simply not sure what could be going on. Engine has about 80K miles on it so not really to many.

I just did a complete oil change as well, as I had read about Oil dilution and wanted to make sure that I had removed that as an issue.

I have read about the following as possible causes but just have know idea where to start.

1. Vacuum pump failure (pressurizes Crankcase and forces oil out the slobber tube (Does a Motorhome with Air ride and Air brakes even have an engine mounted Vacuum pump?

2. Faulty Injectors. Not working or possible burning a hole in the piston.

3. Broken Rings.

Any Help would be greatly appreciated. Thanks in advance.
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Old 07-10-2021, 03:06 PM   #2
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My 5.9 had the occasional excessive blow by and I tracked that down to the heat. So what I did for years is just under fill the crank case. I'd read that both Cummins and Cat have extra room in the oil pan for extra oil. That it was a standard design for them. That it wasn't necessary to have it filled to the brim. I did my research and found that many many RVers under filled to reduce slobber. This eliminated all those work around methods people were doing, like collecting the slobber tube blow by. Seemed a lot of people lowered the amount of fill oil, and remarked their dip sticks.

Once I reduced the amount of oil, very little blow by, and no oil issues. Mainly because RV'ers tend to check and top off their oil level more often than a trucker might.

For example, my Cat engine is a 3126e and had a '22 qts' written on the frame nearby the fill tube by Winnebago. I fill it to 20 qts instead. And the previous owner had already adjusted the dip stick to reflect 'Full' at 20 qts. Zero blow by. Even in the heat.
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Old 07-10-2021, 03:15 PM   #3
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ISB 5.9 , vacuum pump is an early Dodge /Cummins item , before the trucks went to hydro boost brake system.

Bad injector, hole in piston , = crankcase flooded with diesel , lack of power, and EXTREEM rough run .

If you're using the correct amount of engine oil for your changes, and your dipstick is correct so you don't overfill the oil pan .
Pretty sure broken rings would be the issue .

Compression test ( which on the 24 valve is not easy ) is the way to confirm.
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Old 07-10-2021, 03:18 PM   #4
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since I did the oil change right before we left, I know there was only 14 quarts in the pan plus what the oil filter held, maybe another 1 to 1.5 quarts.



Freightliner and Cummins state that the ISB holds between 17 and 19 quarts. At say 15.5qts I was about the middle of the safe zone on my dipstick. when I stopped, I added in 4 quarts, and I wasn't even showing oil on the dipstick, but that is all I had with me,



I stopped and bought 3 more gallons on the way home for the remaining trip. each time I emptied my slobber bottle that was full, 32oz Gatorade bottle, but because of the pressure on the tube is was splattering out.


Stopped about 60 miles from home to add the last gallon.
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Old 07-10-2021, 03:21 PM   #5
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Quote:
Originally Posted by Skip426 View Post
ISB 5.9 , vacuum pump is an early Dodge /Cummins item , before the trucks went to hydro boost brake system.

Bad injector, hole in piston , = crankcase flooded with diesel , lack of power, and EXTREEM rough run .

If you're using the correct amount of engine oil for your changes, and your dipstick is correct so you don't overfill the oil pan .
Pretty sure broken rings would be the issue .

Compression test ( which on the 24 valve is not easy ) is the way to confirm.

I guess this is my next course of actions. I'll see what I can come up with and report back.

It isn't running rough, and I'm not seeing or smelling any fuel in the oil coming out in the catch can.
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Old 07-10-2021, 05:25 PM   #6
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Recommend you send an oil sample in for testing.
Check the complete intake system and check the air filter.
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Old 07-10-2021, 05:56 PM   #7
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Intake system leak, drawing in dust, cause the rings to wear.
Worn rings cause blow-by.

Remove intake hose on intake manifold and feel the inside of the pipe for dust.
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Old 07-10-2021, 07:15 PM   #8
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What a bummer.

Your air brake chassis will have a air compressor.... not a vacuum pump

Oil blowby only can mean a couple of things: compression or air pressure getting into crankcase.
Failed/worn Piston rings
Or
Air compressor Piston rings
Or
Overfilled crankcase/mismarked/wrong dipstick.... however this issue usually stops once oil level gets to the correct "level"

Is any oil coming out of exhaust?
Turbocharger failure will fill CAC and intake with oil and it'll go out exhaust.
Do you see or feel any "puffing" air at slobber tube with engine running?
Remove the slobber bottle and start it up...a little puff is ok...a lot or a steady blow is bad news.

I have been able to control some amount of blow by oil by using a Fleetguard open crankcase ventilation kit, part number CV50115

Be sure to close inspect all air cleaner piping, hoses and clamp after the air filter. Any hole, loose clamp or bad air filter seal will allow dust/dirt in engine and make quick work of wearing it out.

Good luck and keep us posted!

edit.... just reread that it took you 4 gallons of oil to get home... ain't the dipstick, (unfortunately)
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Old 07-10-2021, 10:34 PM   #9
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Simple test. Remove the oil fill cap. Start engine. Place the full cap back on the hole it came out of but donít screw it tight. If it dances around around and wonít stay on at an idle engine is having issues and should have a proper blowby test done.
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Old 07-11-2021, 09:49 PM   #10
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So here it todays progress. We pulled a few injectors and scoped them. Wa seeing some scaring but very little. We didn't have the right adapter to run a mechanical compression test. But we did run a Pico Diagnostics test on it the reads the compression based on apm draw from the battery, lower compression, lower Amp draw.

There was also some dust/dirt on the air inlet so I'm pretty sure that I have compression issues.

Based on the results on cylinder os down 16% over the others, and another one is down 7%, what I don't know is how bad the others are as this is a relative test just comparing them to each other. The other 4 are all pretty similar.

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Old 07-11-2021, 09:53 PM   #11
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Here are 3 videos of the blowby that I am seeing. This from a cold start, temp was at about 120 degrees. Smoke out the breather tub and the oil fill cap.

http://www.saltlakemini-z.com/Motorhome/Blow-by1.mp4

http://www.saltlakemini-z.com/Motorhome/Blow-by2.mp4

http://www.saltlakemini-z.com/Motorhome/Blow-by3.mp4
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Old 07-11-2021, 09:59 PM   #12
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I'll be ordering the right adapter and confirming mechanical compression before pulling the motor.

Looking like a full rebuild is going to be happening.
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Old 07-11-2021, 10:39 PM   #13
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Can it be in-framed? Maybe pull head and inspect cylinder walls, if not terrible, get away with honing cylinders... replacing pistons/rings and crank bearings.

But you'll for sure want to get after the air intake system, was there any loose connection? You see where it got in?

It's a big pita, but no shame, it happens more than one would think.
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Old 07-11-2021, 11:15 PM   #14
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Iím sure you already know that engine is completely dusted. How much dust is in the turbo compressor wheel shaft centre hole? Donít forget to replace the charge air cooler. Oil cooler and air compressor if repairing that engine. No liners in the 5.9. So a proper repair will require engine removal. Is there any cross hatch showing on the cylinders when you scoped them?
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