Engine/Transmission (1994 - 1998) Excessive blow-by after head install??

[JGheen]

Help me out with this one guys, I need your thoughts on why I would be seeing higher blow-by flow out of the crank breather tube. It's not blowing oil out but I would say it is about twice the amount of flow I used to see before the head swap. I was thinking maybe the rings in cylinder #6 needed some time to seat back into the sleeve cuz of the rust ridge I found when I initially removed the cylinder head for gasket replacement. So maybe that cylinder is not sealing as well as the others??

I did not put a flow meter to it but it definately is blowing more vapor than before. Help me out with some other thoughts guys...



Thanks, Joe

 

[NCovey]

Did the head have a valve job done to it. I have seen higher mileage vehicles get a valve job done and start blowing by the rings. The better sealing surface between the valve and the seats over powers the sealing surface between the rings and the cylinder, causing blow-by. -Nicholas

 

[PSchwering]

If you knocked a vacuum line off, or forgot to hook one up, it will give the same symptoms... . P.

 

[JGheen]

Did the head have a valve job done to it. I have seen higher mileage vehicles get a valve job done and start blowing by the rings. The better sealing surface between the valve and the seats over powers the sealing surface between the rings and the cylinder, causing blow-by. -Nicholas

The head is brand new from Piers. New valves, seals, o-ringed and pocket ported.



Joe

 

[JGheen]

If you knocked a vacuum line off, or forgot to hook one up, it will give the same symptoms... . P.

Vacuum line? How? I only disconnected one vacuum line during the swap and the cruise control and heater vents all work fine. I would think if I had a vacuum leak those actuators wouldn't work.



Joe

 

[PSchwering]

I dunno - I had a rubber hose rub a hole on mine, & the vapor from the blow-by tube was enormous. I had no other symptoms- Heat & A/c worked - Brakes worked well. - Just lots of blow-by. Found the problem & fixed - Blow-by by was back to normal. Just something worth checking, in my opinion. P.

 

[JGheen]

Thanks P, I'll give the lines a check and see if that reduces it any.



Joe

 

[JGheen]

Well, that was it. I had a loose main vacuum line up on the cowl area and it reduced my blow-by back to normal.



Thanks guys, Joe

 

[Berrigan]

Well, that was it. I had a loose main vacuum line up on the cowl area and it reduced my blow-by back to normal.



Thanks guys, Joe

Lets talk this out------------how could a vacuum leak cause blow by? Bill

 

[JGheen]

It vents into the crank case as I understand and if a line is loose it will pressurize the case causing higher than normal blow-by which is what I just found to be true just a few minutes ago.



Joe

 

[Berrigan]

Joe. so are you saying the exhaust, if you will, of the vac pump discharges into the crank case. If that is so I can understand how that would increase blow by. But that seems like a bad way to design it. I thought the discharge just vented under the hood, right at the pump. Maybe im wrong. Bill

 

[JGheen]

Thats what I'm sayin. Maybe someone will chime in and confirm me.



Joe

 

[Johnstra]

I haven't studied the vacuum pump to see if there's more to it than it appears, but it definitely vents/exhausts directly into the gear housing and this pressurizes the crankcase when there's a vacuum leak. I know for sure it did on mine.



You're right this is a bad design as vacuum leaks dump unfiltered air into the crankcase!



-john

 

[Vaughn MacKenzie]

Only thing I can guess is it's darned noisy and would be very audible if it didn't exhaust into a big open heavy Cummins diesel crankcase

 

[BPonci]

Does the exhaust have any strange noises that doesn't sound normal? I had a valve seat come loose when the engine warmed up. The low compression made the blowby tube seem to have excessive vapor.

 

[PSchwering]

Lets talk this out------------how could a vacuum leak cause blow by? Bill

It does Not cause blowby. It is pumping air into the crankcase, Which then exhausts through the blowby tube - Giving the APPERANCE of Blowby problems, when the problem is elsewhere. Certain turbo Problems can cause the symptoms as well. P.

 

[Johnstra]

I was just going to post the same thing It's an important distinction.

-john

 

[JGheen]

It was definately my vacuum pump cuz my vapor levels are down to where they should be. After I found the loose main vacuum line the vapor pressure slowed down very considerably. My turbo is still new and my head is brand new as well so I doubt there would be any problems there not to mention how smooth the engine sounds when running now.



Joe

 

[Berrigan]

It does Not cause blowby. It is pumping air into the crankcase, Which then exhausts through the blowby tube - Giving the APPERANCE of Blowby problems, when the problem is elsewhere. Certain turbo Problems can cause the symptoms as well. P.

Ya I was thinking the same thing. Maybe it is a noise issue, and also vacuum pumps move oil out with the exhaust. If it was vented to the air it would be spitting out oil and leak everywhere. If vented to the crank case the oil will recirculate. Bill