Chevrolet Repair: 1990 chevy 2500 blow by problem, combustion gases, piston rings

Question
QUESTION: hi. i have a 1990 chevy 2500 and the problem i have is that when the truck gets reved up to higher rpms oil blows out the dipstick. i replaced the engine oil and the valve cover gaskets and the pcv valve but problem still consists. i am wondering if maybe when i changed the oil that i put in 10w-40 instaed of the 10w-30 it is suppose to take cause i read the book to fast to remeber the right oil. i have been told that it is the blow by created by the exhaust that blows by the piston rings. so they said that the piston rings may be worn but the truck has 109,314 miles, so thats barely anything. how could they be worn. could it also be that the tbi unit is clogged? anything will help! thank you

ANSWER: Hey,

 Yes, blow by is a product of combustion gases either being too much for the PCV system to handle or not managed properly.  Did you check to make sure if the PCV system is plugged?  Take the line off of the bottom of the throttle body and look inside.  It will be sucking like mad because there is manifold vacuum there.  I have seen tehm plug absolutely solid and no pcv = overpressurized crankcase.


Wayne


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QUESTION: well i checked all the hoses and everything and it seems to be clear. i started the truck and then pull the pcv valve out and put my finger over then end of it and it sucked big time. i dont know what else it could be. i put plates on it today and took it for a ride and it seems like it doesnt have the power it is suppose to have. and when i came back i popped the hood to see that there was oil everywhere near the dipstick. what else could there be to check

ANSWER: Hey,   YOu have a major blow by problem.  It could be a broken piston ring or damaged piston.  Its not terribly common but it can happen.  A cylinder leak down test can verify where the combustion gases are coming from and what cylinder is suspect.

W

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QUESTION: off the line this truck doesnt have much but at like 5mph the rear end will break loose. so i know it has the power. could something else be clogged? cause i really dont want to tear down the whole motor to find out that i should have just bought a different truck and not gotten myself into this headache. is there anything i can do or any tricks that would fix this without tearing down the whole top end of the motor? cause i just want this truck to work. also if there was a damaged piston ring or piston wouldnt the truck not run right? this truck runs great!!!! see thats why i dont understand. the other thing i did was take the passengers side valve cover off where the pcv valve is and i took my air compressor and blew the crap out of there. let me tell you the black crap that came out of there. then drove the truck and it seemed to be alright. i check the oil everytime i take the truck and it seems like the oil level on ithe dipstick never moves so i dont know where it is leakin from. thank you for your help because it is greatly appreciated

Answer
Hey,

 The only other thing that could theoretically cause that much back pressure is a plugged exhaust system.  If the cat was plugged solid and the exhaust gases couldn't get out it might be finding a way into the crankcase.  There really isn't anything else that would cause that much crankcase pressure.  Thats where the pressure is coming from.  A cracked ring could still give you compression but cause lots of blowby.

w