Oil leaking from blowby tube

M

mtboggs

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I have a 96 12 valve with 206,600 miles and a couple weeks ago it started blowing oil from the blowby tube. I took the oil fill cap off and started it to see how much blowby is coming out and there's not a lot, not even enough to move the oil fill cap if you just set the cap on top without tightening it. I was told a vacuum leak can cause this so I looked over the vacuum lines and didn't find anything. Also it seems if I keep it under 2000rpms it doesn't do it, and I checked to make sure the oil wasn't over full. I also noticed just before it stared puking oil the abs and brake light started coming on and off also. If anybody has any other thoughts of anything else I can check I'd appreciate it thanks.
 
I'd look into the vac sys some more. If the brake sys detects low vac it can trip that light. Low vacuum probably means a leak which equals a lot of air being pumped into your motor via the vacuum pump. Air in, oil out.
 
If the engine is healthy you could totally disconnect the intake of the vacuum pump and it couldn't cause excessive blowby. That little 3/8 inch hole can't suck in more air than the 7/8 crankcase vent can discharge. It is simple physics. If you have blowby from worn rings, yes a vacuum leak could possibly be the "straw that broke the camel's back" but there isn't any way it could be the cause. Have you ever had an oil sample done to see what the silicon count is? That will tell you how efficient your air filter is, and that is the main reason why low mileage engines have worn rings.
 
GAmes said:
If the engine is healthy you could totally disconnect the intake of the vacuum pump and it couldn't cause excessive blowby. That little 3/8 inch hole can't suck in more air than the 7/8 crankcase vent can discharge. It is simple physics. If you have blowby from worn rings, yes a vacuum leak could possibly be the "straw that broke the camel's back" but there isn't any way it could be the cause. Have you ever had an oil sample done to see what the silicon count is? That will tell you how efficient your air filter is, and that is the main reason why low mileage engines have worn rings.
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We've been seeing blowby problems caused by vacuum pump for years on these engines....WAY more common that worn rings on a 200K miles 12v Cummins.

You can totally block the intake for the vacuum pump to check, but you want to make sure it's a tight seal.

FWIW,
Chris
 
Signature600 said:
We've been seeing blowby problems caused by vacuum pump for years on these engines....WAY more common that worn rings on a 200K miles 12v Cummins.
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We've been reading the internet myth about vacuum leaks causing excessive blowby for years. If you want to believe you can suck more air into a tiny hole than a great big hole can discharge, be my guest.
 
I have seen it myself. Changed vac pump, blowby greatly reduced.

I don't need anyone telling me what is a myth and what isn't, when I have owned my fair share of high mileage, and high horsepower 12v engines.

Chris
 
I've personally seen oil dump out of the blow by due to the hose being broke off the vac pump as well. fix the hose, leak goes away.
 
You could've also blown out a piece of headgasket leading to blowby... At least that's what happened to me for awhile till I blew the front of the head gasket where it leaked oil externally...
 
B N S slammer said:
You could've also blown out a piece of headgasket leading to blowby... At least that's what happened to me for awhile till I blew the front of the head gasket where it leaked oil externally...
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That would be pretty far fetched as well, but it would be a possibility. Would have to blow between the cylinder and push rod passage, but it is "possible."

I would think if you had a compression leak to the push rod passage it would be a bad enough leak to cause a "miss" or a roughness at least.

Chris
 
Heres an odd question. Should probably be in its own thread though. High-torque head studs can cause a tiny distortion in the cylinder liner that will become visible if you do a hone with a torque plate. Perhaps could be enough to lose a small amount of compression as the rings travel over that spot. Never been able to get a solid answer on this, it woud be hard to verify whether it does anything one way or the other. Sure does seem to coincide with my compression woes.

Ive been chasing this gremlin myself. 235k and its to the point where oil oozes out from under the valve covers. Could be turbo too, I just dont have the motivation or money to chase it down right now.
when I had the motor compression tested it made 360psi cold. Not all that good.

Another possibility is a leaking turbo. might be pressurizing the oil drain.
 
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Sorry it took me so long to respond I've been super busy, I haven't had a lot of time to look at it yet but I did check to see if any vacuum hoses have come off and I didn't find any. If it were worn rings shouldn't the symptoms gradually gotten worse? It started dumping oil out one day day and if I keep my rpms under 2,000 it doesn't puke any out. Also it doesn't start hard or smoke like worn rings.
 
I would be checking the turbo for oil in the intake and in the exhaust. Could very well be turbo.
Chris
 
I've had this happen. Like it came out of nowhere. Retorqued the head. Problem gone. Flame suit on.
 
just cheked the intake no oil in it not sure about the vacuum leak, the 4x4 still works and I know if you have a bad vacuum leak it won't work.
 
Mine leaves a drip every where I go it only does some light towing. I've been through a couple turbo rebuilds over the years inter cooler still has a good coat of oil.

f6jbob said:
I've had this happen. Like it came out of nowhere. Retorqued the head. Problem gone. Flame suit on.
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My ford buddy's say I had a nice drive way till I parked the 12v there. LOL
 
I believe the turbo theory is that a bad seal will allow air into the oil line that drains into the sump, which if possible would definitely pressurize the bottom end.
 
ID be curious to see some before and after silicon numbers with an aftermarket air filter also.
 
My father-in-law got his 2001 Dually super cheap because it had this issue. If you got on it too hard, it would pretty well empty the crank case. Blow-by was fine at idle. Dealer had compression tested it and said two cylinders were toast. He filled it with Rislone a couple times with some low-mile oil changes and it improved 100%. Drove it like that for three years before he sold it and bought a 12v. He was a steel shop and towed heavy. We always just assumed the rings were stuck on those two cylinders due to low quality oil.

I find it hard to believe a vacuum pump can cause enough air flow to create a positive crankcase pressure big enough to push oil out of a clear blow-by tube, they're not that high flow. Bad rings on 1 or 2 cyl however, could easily move 50+cfm @ 2000rpm through the blow-by. I also don't buy the turbo theory. Rings, head gasket or maybe even a cracked piston makes way more sense to me. I'm interested to see what turns up from this.....
 
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