Excessive Blowby- Turbo?

VMacKenzie

VMacKenzie

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Dec 9, 2007
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For the past roughly 10k miles blowby has been increasing on my '98.5, especially lately. At idle there is considerable air volume pumping out the vent tube, much more than before, and you can really smell oil vapor. I used to go 4-5K miles between adding oil, now it's 500-750 miles per quart. Also I'm having a lot of oil drips in the driveway, used to rarely get any drips.

My vacuum system seems tight, no leaks that I can find. I pulled the main hose off the vacuum pump and plugged the fitting, but it didn't diminish the vapor stream at all. I don't think it's the head gasket since it's a steady stream, but if it's the turbo is it possible to have that much extra blowby at idle, with no boost? I have a Garrett Stage 3 ball bearing turbo. The shaft play seems a bit excessive, the original owner of the turbo hammered on it pretty hard. Tomorrow if it's not miserable cold out I may disconnect the oil return line from the turbo and put a bucket under it and see if there's vapor/gases pushing out the tube.

Has anyone had excessive blowby issues and have it turn out to be the turbo, even if it seems to be functioning OK?
 
Mopar1973Man said:
Check your vacuum lines first. Typically just cap off the vacuum pump as see if this reduces the blow by. But if that doesn't then you'll have to do a compression test to figure out whats going on.
http://articles.mopar1973man.com/general-cummins/34-engine-system/144-compression-testing

Don't bother with a blow by test it will not tell you which cylinders are damaged just a summation of how much blow which we already know is too much.
Click to expand...


Why not do a blow by test? He has already crossed the vacuum system off. Check turbo and then tear it down for an over haul


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We use a slack tube manometer to measure crankcase pressure. Process of elimination of components is the steps.
 
97rada said:
Why not do a blow by test? He has already crossed the vacuum system off. Check turbo and then tear it down for an over haul


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Click to expand...

Because I've seen where a single cracked piston can and will pass a blow by test but a cracked piston will not pass a compression test because you measuring each cylinder pressure and not a summation of blow by gases like the blow by test. But at least then with a compression test there is no surprises you know exactly what is wrong with the engine.

Like I've had a gent spend large amount of money guessing because a blow by test passed but still had a misfire issues that come and go. Then after all said and done it was #4 piston cracked. When cold it ran perfect but as the piston warmed up it start to drop out. No sign of excessive blow by vapor or oil.

So... Up to the owner what he's planning on doing.
 
The cracked piston issue is interesting. Sure hoping it's not an internal engine issue. This came on rather gradually, too slowly to be a cracked piston, but too quickly for it to be engine wear. I rolled 180k recently but it's never been more than 75hp over stock and EGT kept down and well maintained. It was tight and used virtually no oil 10k miles ago. I checked the air filter and intake last night to make sure nothing happened with that and the motor got dusted but it's spotless. I run a BHAF.

I'm going to rule the turbo out, it that's not it then I'll move on to a compression test. . . I know given how rapidly the vapor is gushing out it won't "pass" that test.
 
I had a chance to do some troubleshooting today and clearly ID'd the turbo as the culprit. I disconnected the oil return line and ran a rubber hose from the turbo into a jug. With the engine idling there was no longer a massive rush of oil vapor blowing out the blowby hose, there was barely a lazy gentle wisp. . . literally was at least 20 times less than before. It's a relief it's definitely not the engine! I could plug the hose with my thumb for 15 seconds and get almost no perceptible pressure buildup.

So now time to buck up nearly a grand for a rebuild, BB turbos are not cheap to rebuild. Hopefully parts are available, unfortunately Tom Spictig said Garrett stopped producing the GT37 series recently.
 
I would have never thought about the turbo. Learn something new everyday.
 
The engine was cool, had not been run for about 3hrs but wasn't bone cold either.
 
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