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  1. #1
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    4S Smoking during start up

    So I've noticed when I start my 4s (15hrs) while it's trimmed down it smokes a pretty good amount just at start up. Yesterday I got on a run and gun sort of pattern, and was hopping from spot to spot; I noticed the blue smoke several times while doing this. I never see this if I have motor trimmed up so thinking it's caused by trim position. So...

    1. Is this normal?
    2. Is it the back pressure from the exhaust port being in water, or the angle of the powerhead?
    3. Is it cause for concern?

    Thanks...Mick
    Last edited by Mick2268; 03-05-2023 at 01:36 PM.
    2018 Ranger 521C, 2023 Merc 250 Pro XS 4S (3B261295), 36V Ultrex, 10" Atlas, Power Poles, Lowrance 12 Carbon, and 2-12 Lives.

  2. Member
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    #2
    The first thing to check is the oil level on the dipstick. The level should not be to full. If you think about the dipstick as 0 to 100%. The level should be about 70-75%!

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    #3
    Oil level, and did you follow the proper break in? Do you ever run the motor at 4500 rpms or so for 30 minutes?

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    #4
    do not trim down while fishing leave it up some to minimize the smoking--seems to be normal issue
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  5. Member
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    #5
    Quote Originally Posted by Capt James View Post
    Oil level, and did you follow the proper break in? Do you ever run the motor at 4500 rpms or so for 30 minutes?
    Yes I followed the break in, and I drive in the 4kish rpm range 90% of the time.
    2018 Ranger 521C, 2023 Merc 250 Pro XS 4S (3B261295), 36V Ultrex, 10" Atlas, Power Poles, Lowrance 12 Carbon, and 2-12 Lives.

  6. Member
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    #6
    Mine does the same thing. The dealership I got it from said on his boat its the exact same. Remedy is to leave it trimmed slightly up and it will correct it. Like other posted before me make sure your oil levels are correct too.

  7. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #7
    Quote Originally Posted by 5keepers2 View Post
    The first thing to check is the oil level on the dipstick. The level should not be to full. If you think about the dipstick as 0 to 100%. The level should be about 70-75%!
    See the FAQ Section for more information on this topic.

    Oil level should be at 25-35% of the safe zone.

    Mick: Per the engine owner's manual, always raise your engine to at least a slightly positive trim angle when shut down or turned off. This will help.


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  8. #8
    my engine did the same and i called the factory and they said that's normal and to raise the engine a little so i do when i shut it off and it stopped and only smoked very little once in a while that's absolutely normal mercury said. for my 250 pro xs 4 stroke 2020 they know all about it

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    #9
    OK thank you, that is at least a relief, even if it is a pain in the hiney when trying hit a bunch of spots really fast. I'm sure I'll adjust.
    2018 Ranger 521C, 2023 Merc 250 Pro XS 4S (3B261295), 36V Ultrex, 10" Atlas, Power Poles, Lowrance 12 Carbon, and 2-12 Lives.

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    #10
    Good that Mercury says it is normal. But when I 1st read the original post, the 1st thing that came to mind was piston rings. Usually when a 4 stroke smoke's it means oil is getting past it's piston rings and getting burned out the exhaust. Thus Smoke.

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    #11
    In the old days of radial piston airplane engines, it was mandatory to use the propeller blades to rotate the motor several times by hand. To ensure that any oil that got past the piston rings in the lower cylinders did not hydrolock the motor. If hydrolock was encountered, then spark plugs had to be removed to drain out the oil.

    Something similar happens when four stroke outboard motors are tilted downward.


  12. Member haus9393's Avatar
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    #12
    This is what I know about my 4stroke 250 pro xs. It’s got about 600-700 hours on it. I can’t remember the exact number as I haven’t started it in 3 months. Anyway it’s smoked on start up since I got it. Everyone I know with the motor has this happen but it’s not all the time. It occurs probably 10% of the starts so if I start the motor 30 times a day it might happen 3 times. When I change my oil after about 100 hours of run time I find I am about 2 quarts low on oil compared to the normal level of 7 quarts. One time I had the low oil alarm go off and I was about 3 quarts low so I had 4 quarts left in the motor of the original 7 I had put it. So where does the 2-3 quarts of oil go? I’m guessing it’s burned off like the image above when I start the motor.

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  13. Member
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    #13
    If the motor is left trimmed down then the oil consumption is going to go up. Oil that would otherwise have flowed to the oil pan will flow to the combustion chamber. Resulting in smoke at start up. The greater the number of stops and starts with the motor left improperly trimmed results in greater oil consumption. Wasted oil actually.
    Last edited by yam911; 03-16-2023 at 12:29 PM.

  14. Member haus9393's Avatar
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    #14
    Quote Originally Posted by yam911 View Post
    If the motor is left trimmed down then the oil consumption is going to go up. Oil that would otherwise have flowed to the oil pan will flow to the combustion chamber. Resulting in smoke at start up. The greater the number of stops and starts with the motor left improperly trimmed results in greater oil consumption. Wasted oil actually.
    I wonder why they don’t offset the power head so it sits parallel to the water surface when trimmed all the way down. That would help with this right? I get you can trim up to level when you shut down but I just have the habit of trimming all the way down when coming off plane and forget to raise it while it sits.

    I probably sound like an idiot for the above paragraph because the way the motor sits is how it has to sit in order for everything to work how it does but just a thought.

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  15. Member
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    #15
    It could be done but it would require a universal joint of some kind. More weight, more complexity, more maintenance, more cost, one more thing to go wrong, etc..

    I would just live with a bit of smoke at start up or a bit higher oil consumption if I wanted to trim the motor fully down at each stop.

  16. Member 22R's Avatar
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    #16
    Sounds like it wants to be a two stroke

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  17. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #17
    Quote Originally Posted by yam911 View Post
    It could be done but it would require a universal joint of some kind. More weight, more complexity, more maintenance, more cost, one more thing to go wrong, etc..

    I would just live with a bit of smoke at start up or a bit higher oil consumption if I wanted to trim the motor fully down at each stop.
    +1... because the driveshaft (nor the crankshaft) are meant to be "flexible".

    If you don't overfill the engine with oil (BTW haus... you will almost NEVER add 7 qts of oil to one of these!), and you keep the engine parked with a little positive trim, you'll see very little (if any) smoke.


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    #18
    . you will almost NEVER add 7 qts of oil to one of these!)

    I changed my oil and lower unit gear lube about 2 weeks ago. I went to my dealer to get my oil and gear lube that morning,still had a spare oil filter and another gallon of oil. Not a service tech,just the guy ringing me up says "you know that motor takes 7 quarts of oil,right?" I just smiled,told him I still had a full gallon at home,but always remembering Don's instructions with the dipstick ^^^ being "just right",and knowing some places could be overfilling.