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Hello there. 2008 6.4 had a glow plug code come up, changed it code still came up. Pit in a new gpcm code code still came back now im going to put on new gp harnesses. With that being said after i put on the new gpcm i noticed smoke coming from my oil fill canister, the hose had come off and i reinstalled it but then i took off the fill cap while the engine was running and there is smoke coming out. Normally i associate that as an engine having blow by. Is this normal for a diesel or am i totally screwed and need a rebuild. Thanks in advance.
 

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That depends on the amount. The 6.4s gave low tension piston rings so there will be some blow by. When it starts spitting glow plug harnesses out you have a problem.
 

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The rings in the 6.4 aren't normal shaped rings we typically see and are used to, they're tapered half way down one edge intended on allowing blowby at idle for emissions dumbness. One of those "Certified Clean Idle" bullchit things. When you get on it tho, the compression blows against that taper and it swells the ring wider and it seats harder. So the old upside down oil cap test isn't as accurate as it is on others.

I always use zero-gap 2nd rings when I build them.. And if you plan on running your 6.4 at all hard note that for when you have to rebuild it. But then it'll last forever.
 

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That depends on the amount. The 6.4s gave low tension piston rings so there will be some blow by. When it starts spitting glow plug harnesses out you have a problem.
Is "low tension" the formal mechanical term for rings that need to be replaced with Mahle?
 

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the low tension rings they are built with are designed to allow some blow by until there is a load on them. The aftermarket cp20 mahle rings dont have the same design of the factory ones
 

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I don't know anything about special rings it uses, but all turbo engines will have quite a bit more blow-by. The hotter the engine, the more end gap is needed. Also the more compression, the bigger the end gap.
 
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