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Thread: Olds 455 question on PCV and Blow-by

  1. #1
    diggler
    Hey everyone, just a question I thought up. I lose about a quart of oil everytime I go out. It's pretty much burned off somehow or other. The compression tests are good on all cylinders. The heads were just rebuilt last year with new springs, valves, and rockers.
    Here's what I did do different. Prior to putting in the PCV from the valve cover back to the carb, I had some pretty wicked blow-by. It would blow oil out of the dipstick all over the place.
    I'm thinking that now it just gets sucked throught the PCV into the carb for burning up in the cylinders. Does this sound right?
    One of the other bits of "evidence" I have is that ever since I put the PCV in, there is now black soot all over the back of the boat and all over the pump that is coming from my OT headers. Not a big deal, just some extra cleaning to do as it comes right off. Also, I did put an oil cooler in, and that is helping the situation some as well. Thanks!

  2. #2
    Kindsvater Flat
    Instead of doing a compression test, do a leak down. If you're blowing that much oil you might have a bad ring/rings that are not sealing. Its not uncommon to have good compression and have quite a bit of blow by.
    Do this..... at an idle with the pcv in, vents plugged, see if there is vacuum at the the oil fill. If there is fine. Now do the same thing at lets say 2500 and see if there is vacuum.

  3. #3
    Wet Dream
    Mine does the same thing. The only thing I can come up with is that since there is a lot of oil in the valve covers under a hard run, the PCV is sucking it up and running it through the intake and buring it off. I get a little blow by, but not a quarts worth. The insides of my OT's are blackened so thats my theory.

  4. #4
    diggler
    Wet Dream:
    The insides of my OT's are blackened so thats my theory. Since I put the PCV in, no more blow by. BUT, my OT's are blackend inside like crazy. Kind of nasty, but at least it's on the inside of them. I'm not sure how to perform a leak down test though. I'll be chasing some friends this weekend to see if they can do it for me. Other than that, the boat still does over 70mph so I don't have much to complain about (a jet). thanks!

  5. #5
    Wet Dream
    NICE!!
    What kind of revs are you turning with that 70mph? Are you running a Berk A impeller?

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