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  1. #1

    Default ye ol 671 is smoking white when cold

    The 671 inline is giving us a little while smoke. When she warms up and gets underway, it goes away. We are also getting a faintly detectable sheen on the water at the dock after start up.

    I think I got this one. Injectors probably need cleaning, and the white smoke and faint sheen are due to incomplete combustion.

    I'm checking in here for opinions, and other things I might take a look at while we are sorting this one out. Other possible problems etc.

    I did get one guy tell me to blow out the diesel return lines as clogging there might be an issue. Seemed pretty unlikely to me. Comments on that?

    As always, thanks for any input.

  2. #2
    Join Date
    May 2015
    Location
    Oregon
    Posts
    169

    Default Re: ye ol 671 is smoking white when cold

    Depending on the model, the fuel pump pumps 35 gallons an hour or more. It's a gear pump and should blow out any debris that went thru 2 filters. I doubt you have a return line clog. The fuel is part of the injector cooling. Fuel continuously goes thru the injector tip. If there as a blockage the tip wouldn't be adequately cooled and all the tips would burn out if there was enough fuel flow, in spite of the clog, to reach maximum hp.
    Most Detroits with a few years on them smoke a little when cold. Until the engine is warm, you aren't getting proper combustion. A block heater used for a couple hours before starting should make the smoke go away. If you don't know the history of the injectors, you could have them rebuilt.
    The other possibilities are worn rings & sleeves, leaky turbo oil seal, or leaky blower oil seals. Remove the air silencer and look for oil on the blower rotors. If a turbo model, look for oil signs in the air path to the blower. Take a compression test if you suspect the cylinders are worn.
    The Coast Guard isn't going to come after you for a barely noticeable sheen.

  3. #3

    Default Re: ye ol 671 is smoking white when cold

    Thanks for the thoughts Lepke.
    Update from the boat, running it up to 1500 rpm greatly increases smoke output, running at the 1100 we generally back and forth at doesn't seem to be a problem. That suggests to me that I'm looking at more than just a old cold engine.

    We are in HI, engine starts the day at a pretty warm.

    I suspected that clogged return line not a thing.

    There is no turbo on this baby.

    It been a hot minute since we actually did a valve adjustment, that seems like a simple in house item we can check off (read that and timing could be contributing factors). We have sonicators for cleaning injectors, so we'll do that too (getting someone to do a rebuild out here is like winning the lottery). Compression test seems like a good idea when we have things apart. We'll add that to the list, might point to a more serious issue.

    We got a plan of attack, glad to have you pointing out things to look for.

  4. #4
    Join Date
    May 2015
    Location
    Oregon
    Posts
    169

    Default Re: ye ol 671 is smoking white when cold

    White smoke could also be steam - water. But you would be loosing coolant. And that would be a head gasket failure, but not too common in marine Detroits unless they get hot.

  5. #5

    Default Re: ye ol 671 is smoking white when cold

    I read somewhere on this forum in an old post or online: Put a piece of paper in front of the smoke until it gets wet. If the paper dries out it is probably coolant, if the paper doesn't dry out that probably means there is diesel in the smoke. We are doing that today to try and get some information.

    Next week we are lining up a work day to do 1) valve adjustment 2) injector cleaning 3) compression test. We'll be muddling our way through the last one as we only have one guy that has done in on gas engines before. We may fail on that, but we'll still close it up and run it and one of the first two might solve the issue.

    I'll report back here when we get some data.

  6. #6
    Join Date
    May 2010
    Location
    DC Burbs/Maryland Eastern Shore
    Posts
    2,299

    Default Re: ye ol 671 is smoking white when cold

    On diesels, generally speaking, white smoke equals water/coolant. Grey smoke is normal, black smoke is incomplete combustion and blue smoke indicates engine oil.
    Practicing the ancient art of ren-ching

  7. #7
    Join Date
    Nov 2009
    Location
    temecula, ca., usa
    Posts
    3,992

    Default Re: ye ol 671 is smoking white when cold

    Actually, there's no such thing as "white smoke"....

    If you see what looks like white smoke it is either steam from internal coolant leakage or maybe a faulty exhaust system.

    Or, it is raw fuel vapor that has not been ignited. Typically due to low compression.

    While I kinda like the paper trick you mentioned Matt, It's probably not necessary because raw fuel vapor has a distinct and unmistakable odor while steam has a particular smell too. Especially if it's an antifreeze mixture.

    I'm interested in what you find with your testing so I'll be lurking for sure ;>)

    Good luck.
    Last edited by jgmo; 10-10-2021 at 02:06 AM.

  8. #8

    Default Re: ye ol 671 is smoking white when cold

    It occurs to me that I never posted the results of our testing.
    Someone smarter than me pointed out that on this engine we could isolate a cylinder problem by disconnecting the fuel supply to each cylinder and watch the smoke. We did that and since the smoke didn't change at all for any of them he asked "when is the last time you serviced the injectors". Since I bought the boat in 2017 and the answer is "sometime before then", I decided it was time to buy a new set, and service the exisiting ones. (something I can do without down time). While it is possible that is not the problem, it may be, and sounds like that is deferred maintenance that needs to be handled anyway.
    I'll come back and post when they are installed.

  9. #9
    Join Date
    Nov 2009
    Location
    temecula, ca., usa
    Posts
    3,992

    Default Re: ye ol 671 is smoking white when cold

    I'm assuming that you used jumper lines to bypass the injectors just as you would need to doing compression test.

    Nothing wrong with having a spare injector or two but having a whole set to go to is a really cool luxury!

    And....they store really well if kept in a sealed container with a desiccant pack. They won't spoil like your bananas ;>)

    Just ensure that the tips are really well protected if you will be keeping them on board.

    Thanks for the update! Looking forward to how this turns out..
    Last edited by jgmo; 10-29-2021 at 05:45 PM.

  10. #10
    Join Date
    May 2015
    Location
    Oregon
    Posts
    169

    Default Re: ye ol 671 is smoking white when cold

    An injector shop can test your injectors and rebuild as necessary. No real need for a 2nd set. You could have worn tips. When the fine holes get bigger, some or all of the spray becomes large droplets that don't completely combust and could be the cause of white smoke. If you have a lot more smoke at higher rpm, you should notice higher fuel consumption. If your smoke is bluish, it's oil, and can mean bad rings or sleeves. But if it's a turbo diesel, the turbo oil seal could be leaking and you'd see oil sign in the tubing to the blower..

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