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I rebuilt a 2000 model 5.9 recently and It is having some crankcase vent oiling problems like in the previous post. Its in a school bus fyi. The old motor was slopping oil out pretty badly on the left front of the motor and I discovered part of the problem was a leaking front cover gasket but even after fixing that it still puked a bunch of oil out of the breather tube to the tune of 2-3 quarts a week (400 miles). The motor ended up getting low enough compression in the front cylinder that it started missing a little, so I pulled it out and rebuild it. I have about 500 miles on the motor now and since its used as a spare it only goes out on occasion. What it does is if its on a short route that putts around it doesnt have any problems at all. At idle speed there doesnt seem to be hardly any blowby but if its on a long rural route it will blow 2 quarts out in 80 miles. I had a cummins tech out the other day to look at another bus so while he was here he looked this one over and says there isnt any noticible blow by, we power braked it up a couple times and he said it still looked good. I wondered if maybe I broke a ring or something when I assembled it but it doesnt show any evidence of that running it here in the shop. He says he has had several cummins motors that showed the same symptoms and he has found either bad valve seals on the intake valves which mine shouldnt have since its all brand new, or a bad turbo that will actually push boost pressure into the crankcase through the turbo drain tube when its under boost running down the road.. He thinks I may have a problem with my turbo. He said he has an ISX in the shop right now that seems to have the same thing wrong with it, when you dont work it hard it doesnt push any oil out of the breather but when you cruise down the road it pushes lots of oil out. Have you guys ever heard of a turbo diong that? The shaft play feels real good on the turbo, can it feed boost into the turbo drain line under boost without it showing signs of it pushing oil into the compressor side when not in boost?



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Wow, this is a new one on me (The turbo 'leaking' like this) . . . . I would think it is possible but it should have signs of being worn out (Shaft / End Play or rubbing the housing, etc.)

I would also check out the breather itself. Doesn't it have baffles inside to keep the oil from being blown out with the normal blow-by? I thought it possible for a few to have problems and blow out lots of oil in an otherwise sound motor. If there is not excessive blow-by I would suspect something like this happening.

Only way I can 'safely' think of checking blow-by down the road is rigging up an 'extension' hose to bring the end along the outside driver's window to see how much is coming out doing down the road. Or a dyno.

Make sure you let us know what you find!

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:wall: Don't get jerked around...

Have the shop do a copmression test and be sure. I've seen several trucks now with a damaged piston or rings in a single cylinder pass the blow by test but now do a compression test you'll have a single cylinder way low in pressure. Now a single cylinder is not enough to fail a blow by test and a blow by test is a average sum of all blow by.

Compression Test


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