excessive oil use in 6.5

I have a'96 GMC with a 6.5 turbo. It is using a bunch of oil. Oil is coming out around the air hose that go to the turbo, take the oil filler cap off and no blow by pressure. This truck has 135,000 miles and is not worn out. I read in this forum so time ago about a vacum valve not working right and sucking the oil out of the engine. You guys may have the answer let me know.
THANKS

Your engine has excessive blowby and needs to be rebuilt.

The crankcase ventilation system spews the oil-laden blowby into the rubber elbow ahead of the turbo and that is the mess you are seeing.

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There IS a valve called a CDR (crankcase depression regulator) (ACDELCO Part # CV916 GM#25098706) that closes in case of a clogged air filter to prevent the engine from drawing a high vacuum on the crankcase and these CAN go bad and leak and there's outfits selling them on fleabay as a cure for the problem you are seeing and probably there are a FEW instances where that is what is needed but 90+% of the time there is simply excessive blowby. Spend the money, if you like, then report back here as to what the results were. (LOL!)

I used to LOVE those diesels and still own a couple, the sad truth is they were a REALLY pathetic excuse of a "truck" engine.

Bottom line is, without ring sealing problems that dump combustion products into the crankcase you ain't gonna have the problem you are seeing.

Pull the intake hoses off the turbo and look for oil in the hoses, then check for movement in the turbo compressor wheel. If it's touching the housing or moving around then the bearing is shot. Replace or fit a new center section to the turbo. If it's pulling any amount of oil through the turbo the engine could run off on you. Fix now...

Rod

"Pull the intake hoses off the turbo and look for oil in the hoses"

Problem is the crankcase ventilation system dumps into the hose AHEAD of the turbo and there' ain't a 6.5 out there with a turbo intake hose that ISN'T oily, even with a relatively GOOD engine.

Good point, though, Rod, a failing turbo CAN dump oil into the intake.

In the real world, though, there's about a 97% chance of excessive blowby, 3% chance of an oil-spewing turbo.

SMALL chance, but it IS possible.

The point is that he check the compressor wheel... and I'd be surprised if the odds wern't more like 50/50 given the way most people drive... full bore to a stop, then turn the key off... and then listen to the wind down for 30 seconds.

Rod

Rod, a couple of friends were GM techs back a few years ago and you wouldn't BELIEVE the amount of 6.5 turbos that got replaced trying to cure the "oil in the turbo" problem.

You are correct, the turbo MAY be the problem but the odds are stacked, big time, against that, towards excessive blowby from a POOR engine/piston/ring design.

The old joke about GM diesels says that they are just better than walking!!! Cummins is the only way to go.

I can't say for sure what your problem is . . . but it's pretty easy to pull the pressure-hose off the turbo and check it. Look for too much side-play, signs of scrubbing, etc.

Yes, 6.2s and 6.5s will blow out oil like crazy if the crankcase-venting system stops working. I wish they just used to old pre-emissions draft-tube like a farm tractor.

Not long ago, my turbo 6.2 starting blowing oil all over the road. Never used any oil to speak of previously. Then, all-of-a-sudden, I lost 4 quarts in 50 miles. Guess what the problem was? Oil filler cap up to had fallen off and stop the crankcase vent system from working. I was at least 50 miles from the nearest parts store and they did NOT have the cap in stock. So, I cut out a chunk of my rubber floor mat and used a hose clamp to seal off the oil filler tube. Then drove 300 miles and didn't use a drop of oil. Later a $2 cap from NAPA fixed the problem correctly.

Note that the same thing happened to a friend of mine, in his 95 Dodge-Cummins truck. He was on a trip down south and oil started blowing out his rear main-seal. The repair shop said they'd have to pull the engine apart and he'd be delayed a week. He couldn't wait, so he bought two 5 gallon pails of oil and kept driving. Later, after it got even worse, another shop fixed it in 10 minutues with NO parts. It was a crankcase-vent problem.

Your engine uses a CDR , i.e. a crankcase depression regulator. Believe it or not, General Motors recommends that you replace both the oil filler cap AND the CDR valve every 30,000 miles. If I had done that, my old cap would not have fallen of and caused my problem. Gasket dried out, cap fit loose, and fell off on a bumpy road.

GM test for your vent system is this. Attach a water-manometer or equiv. to your dipstick tube. At engine idle, it should read no more then one inch. At 2000 RPM, 4 inches max.

Cummins is a good engine, it just comes in such a lousy crate...