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what causes an exhaust to smoke?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by MudNurI, Jan 5, 2003.

  1. MudNurI

    MudNurI 1/2 ton status

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    sorry for the idiot of the month questions...

    When I start up my truck- clouds of white/grey smoke come out of both pipes..once it's warmed up, it doesn't do it...when I drive down the road like a normal person, it's fine. if I get after it, she smokes.

    What to check..???

    thanks
    Brandy
     
  2. Sandman

    Sandman 3/4 ton status Author

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    Water in the combustion chamber will do that. Sounds like either the block or the head is cracked. When it warms up the metal expands and the leak is sealed off. just a guess.
     
  3. 90K5

    90K5 1/2 ton status

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    Is it cold outside?
     
  4. BigBurban350

    BigBurban350 1/2 ton status

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    Sometimes when an engine sits oil will leak into the cylinders from the valves and smoke at start up. Blue smoke is oil, Black smoke is fuel, and White smoke is coolant. Or your piston and ring clearances may let oil past on a cold start up causing smoke, and then it seals when it warms up and expands. If your vehical smokes all the time its your rings, if it smokes on engine decel like when your shifting its your valve seals. Also, H2O is a by-product of combustion and will be visible in its gas form on a cold day at start up. /forums/images/graemlins/usaflag.gif /forums/images/graemlins/burb.gif
     
  5. TX Mudder

    TX Mudder 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    what causes an exhaust to smoke?

    [/ QUOTE ]

    Usually, peer pressure - you know, a desire to be 'cool'


    Water being steamed makes white smoke. That's all I can help.
    -- Mike
     
  6. imiceman44

    imiceman44 1 ton status

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    What you call white smoke is actually the blue, or grey smoke mentionned here.
    The way your engine acts means the valve seals are leaking.
    You might even have worn guides. Usually if the seals leak, they accumulate some oil in the combustion chamber, and when you start it , the oil burns untill it's dry.
    Wen the valves are moving as in the engine running, the oild can't pass easily or not much, so yo get little or no smoke.
    Now when you puch the skinny pedal and the valves have to move faster and under pressure, if the guides are worn the valves would wiggle and oil would seep and you will have smoke in puffs usually when you press hard.
    I would suggest you take off the heads and rework the heads (guides, seals and maybe reseat the valves)
     
  7. K5thatShmobs

    K5thatShmobs 1/2 ton status

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    I had this same problem... I would get a lot of blue smoke at startup as well and when I got on it. When I was doing some exhaust work and I had to make a small trip running just the Y-pipe and no cat, I noticed I didnt see anymore blue smoke. The cat (catalytic converter) turned out to be the problem. Check it out especially if its old.
     
  8. Sandman

    Sandman 3/4 ton status Author

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    How bad does it smoke?
     
  9. MudNurI

    MudNurI 1/2 ton status

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    right now, when it sits for up to a week between starting- it will smoke black smoke...enough to make nice marks in the snow banks next to it.....more so when I step on it, while in neutral.....in the summer, when I drive it every day- it only smoke a bit when I start it...nothing major- maybe for 2-3 seconds...you can still see the rig so it's not much smoke! When I step on it- and really get after it, it will blow smoke- sort of like our Duramax does when I get after that...

    Guess it's almost time to put the 305 to rest...I'm not going to pull a 305 with 200K on it, and have it machined...I'll find somethng else to swap in it's place...

    thanks for the help, at least now I know..

    Brandy
     
  10. Sandman

    Sandman 3/4 ton status Author

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    That might be rings. Sounds like its just a high miled motor. might be time for another. /forums/images/graemlins/tongue.gif
     
  11. cheyenne_77

    cheyenne_77 Registered Member

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    Yeh it does sound like rings. Do you free rev it often? (killer to an engine) White smoke you will find is moisture accumilation in the exhaust system. This might sound stupid but if this is the problem, you will find that if you park it in a dry area you will get less accumilation and therefor less smoke. But if tthere is a tinge of blue in your smoke then i'd say it is either rings or valve guides/seals. Hope it helps some.
     
  12. Blazer1970

    Blazer1970 1/2 ton status

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    If it is cold out, you will get a lot of white "smoke" out the exhaust at start up. This is condensation, and it is completely normal.

    You may have worn valve seals as noted by others above. This causes blue smoke at startup in all temperatures, and maybe some blue smoke under hard acceleration.

    As long as you are not using excessive amounts of oil (more than a quart in 1000 miles or so) or losing coolant, and you are not fouling plugs, it is really nothing to worry about. Just keep driving it and changing your oil at 3000 miles or so, and it shouldn't get worse.
     
  13. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Black sooty smoke at start up is to much fuel miss adjusted choke. Not really a problem if it isn't fouling out the plugs. White smoke on a cold morning is again nothing to worry about. It's to condensation being run out of the exhaust and can be partly due to a rich fuel mix.
    Black smoke when you get on it is too much fuel. a little is ok but a lot is not. It's using more fuel then it needs. this could also be back to a miss adjusted choke.
    Blue smoke on start up andtaking off after iddling is usualy bad valve guide seals. If you pull the plugs and have a lot of light brown crud on the spark plugs is also another indicator.
    Blue smoke all the time is rings.
    White smoke that continues after fully warm and a sweet smell in the exhuast is water in the combustion chamber. Usualy blown head gasket but 305's are prone to craked heads in the water jacket behind the valves. You will notice that you will need to add coolant a lot for these conditions.
    Really what your describing sounds more choke related to me. possibly mixture control solonoid if so equpped. Not really a big worry as I see it. Drive it till it blows or it smokes all the time. Start setting aside some cash and get a crate when you get the money but I would say your not going to have to do something other than maybe adjust the choke till summer.
     
  14. chevyracing

    chevyracing 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />

    what causes an exhaust to smoke

    [/ QUOTE ]

    The engine.....the engine will cause the exhaust to smoke. /forums/images/graemlins/grin.gif
     

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