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Technical smoking sbc

Discussion in 'The Hokey Ass Message Board' started by Los_Control, Sep 23, 2019.

  1. Los_Control
    Joined: Oct 7, 2016
    Posts: 601

    from TX

    This is a mystery to me, I wonder if any kind people here, can help explain whats really going on.
    This 350 runs perfect, does not smoke or burn oil, the exhaust pipe was coco brown when I bought it.
    I then changed the oil maybe 4 times in about 2 years 6k miles, try to flush it out.

    Now it smokes, but only when at idle for extended periods of time.
    If I start it up and drive it and stop at a traffic light, thats fine it does not smoke.
    If I start it up in the morning and let it idle for extended period of time it smokes.
    If on the freeway and run into road construction, then idle for long period of time, after say 5 min, then it starts to smoke. Then road clears up and within a mile or so, no more smoke.

    Just looking for ideas on what others think is causing it.
    I think I changed the oil often and knocked sludge loose and blocking the return oil ports.
    Now it is overflowing into the chambers and burning at idle.
    Is that even possible?
    Thinking maybe add some seafoam to the oil and change it again.

    This motor with a manual transmission is a kick in the pants to drive. Will run 90 mph down the freeway all day long and not burn a drop of oil.
    Let it idle for 5 min and starts smoking.
  2. Doublepumper
    Joined: Jun 26, 2016
    Posts: 444


    First thought is bad valve seals. I'd do a leak down test first.
  3. Los_Control
    Joined: Oct 7, 2016
    Posts: 601

    from TX

    I do not have the tool to do a leak down, can do compression. I will need to make it up.
    In the past, my old sbc with a common leaking valve guide problem, would puff out smoke when they sat over night and start up.
    This motor does not puff out smoke when first started, only smokes after extended idle.
  4. rockable
    Joined: Dec 21, 2009
    Posts: 2,624


    Either valve seals or PCV would be my guess.
    X-cpe likes this.
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  5. Pull the valve covers and see if there is goop &gunk clogging up the oil return passages in the heads. at idle you have high vacuum you could be sucking oil thru a PCV . or maybe a intake manifold gasket?
  6. Los_Control
    Joined: Oct 7, 2016
    Posts: 601

    from TX

    Possible the intake, I did not think of that ... the pcv valve does shake rattle and roll, and I sprayed some cleaner in it. Just trying to eliminate the pcv from the equation, it seems to be fine. Going to replace it though.

    Once I posted this thread, I then read it and thought ... pull a valve cover and find out.
    This motor/trans/rear gear really puts a smile on your face. I was told it had 50k on the motor.
    But is old and been sitting.

    Just trying to get some ideas before taking it apart. Trying to understand what is going on with it.
  7. el Scotto
    Joined: Mar 3, 2004
    Posts: 4,153

    el Scotto
    from Tracy, CA

    I second the high vacuum sucking oil in somewhere... :cool:

    Maybe you could block of all the vacuum ports as an experiment?
    ffr1222k, X-cpe and Los_Control like this.
    Joined: Dec 14, 2009
    Posts: 1,898


    Pcv stuck
    Plumbed in wrong
    Intake manifold leak
    Vacuum leak

    I’m not thinking rings, valves or guides as it’s not smoking constant or when cold , cold starts is usually when you see oil burning with worn guides or seals.
    ffr1222k and Los_Control like this.
  9. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 4,705


    It's not likely to be plugged oil return passages. There is a lot more oil moving when you're running "90 mph down the freeway all day long" than there is at idle. If return passages were plugged you'd be starving the bottom end after a couple minutes of running 90 mph because all the oil would be stuck under the valve covers.
    Los_Control and Blues4U like this.
  10. Los_Control
    Joined: Oct 7, 2016
    Posts: 601

    from TX

    This is what I kinda think but not sure.
    It is a newer engine in a older vehicle, the intake has been changed.
    Just because the pcv works, does not mean they installed it correctly ... I have to check this.

    And of course the manifold leak, I would think this to be like a vacuum leak. Affect the tune of the engine.
    I honestly would drive this engine anywhere and not want to touch the tune of it.
    The idle is perfect, the response is perfect, gas mileage sucks, I would not change a thing.
    VANDENPLAS likes this.
    Joined: Dec 14, 2009
    Posts: 1,898


    If you can find out the year of the engine
    What valve covers where on it new ( vented, non vented)
    What type of pcv system it came with from factory
    Fueli engine converted to carb
    Egr engine?

    Cheap n dirty
    Cap and or remove all vacuum stuff
    Get an oil catch can like the dragsters and tuner folks use and get rid of your pcv set up and report back.

    Google and YouTube oil catch cams lots of homemade stuff you can do for basically 0 dollars.
  12. Just for fun......"smoke" or lack there of comes in many colors....... What we talking here? White/Black?/Blue?
    Plz elaborate...:confused:
  13. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,275


  14. Mr48chev
    Joined: Dec 28, 2007
    Posts: 25,529


    How much oil is it going through? If it is burning that much oil every time it warms up you have to be adding oil on an all too regular basis and you haven't said a thing about how much you have to add.

    Smoke at an idle when stopped in traffic could mean a carb that is running far too rich just as well as burning oil. Especially if it acts up and runs rough. The oil burning probably wouldn't have as much effect on the way it idled.
  15. Ralphies54
    Joined: Dec 18, 2009
    Posts: 698


    He did say the mileage sucked, probably a carb problem and not oil. Ralphie
    VANDENPLAS likes this.
  16. A PCV is a vacuum leak. its a metered leak. you tune your carb to compensate for it. a intake leaking you could also have the engine tuned to compensate. Ive seen improperly baffled PCV,s that sucked oil. Ive seen engines that had broken rings run great and only blow blue smoke under certain conditions. Pull your PCV how much blow by does your engine have? On a chevy V8 If its very much at all you need at the very least new rings.

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