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  1. #1
    Commander sutor623's Avatar
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    Default Can I run 25:1 oil mix when it calls for 50:1?

    Hey guys I have a big ol' 10 gallon tank that I use for my Merc 650 (50:1), and a 3 gallon reserve tank. The 3 gallon tank is mixed 25:1 for my kicker. If I use the reserve tank (25:1) for a motor that calls for 50:1 will it cause any misfires or idling issues?

  2. #2
    Moderator JB's Avatar
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Using the 24:1 will not harm your Merc. You might need to clean your plugs and decarb your engine more often, but that is all.

  3. #3
    Commander sutor623's Avatar
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Quote Originally Posted by JB View Post
    Using the 24:1 will not harm your Merc. You might need to clean your plugs and decarb your engine more often, but that is all.
    Alright thanks as always JB! Just figured it was a viable question.

  4. #4
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Actually your carb is jetted for x amount of gas. If you run double oil your engine will run lean. It will be masked by the abundance of oil, but it will be lean.
    When will people learn that impellers require regular
    replacement and are not drive it till it pukes items?

    1984 Regal Medallion 195
    3.8 V-6 with the dreaded
    OMC Stringer Drive.
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    If it ain't fixable - don't break it!

  5. #5
    Lieutenant Junior Grade marc c's Avatar
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Hi. Just curious what kind of a kicker takes 25:1?
    I haven't seen that for a long time.
    1974 Glastron V-179, Mercruiser 140
    1984 16.5ft. Alumarine Sealark side console with 82 Merc 50
    Homeport - Lac du Bonnet, MB, Canada
    I've used Fram oil filters in all my junk for 35 years-no problems

  6. #6
    Commander sutor623's Avatar
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Quote Originally Posted by marc c View Post
    Hi. Just curious what kind of a kicker takes 25:1?
    I haven't seen that for a long time.
    Sure Marc. Well technically, it calls for 48:1 from the factory. It is a 1969 Johnson 4hp 2 cyl. These motors have one bearing in the crank case, so everyone with experience with them says it is better to run it at 24:1. Otherwise we have seen them run hot, or just blow up. BTW, she runs like a sewing machine......

  7. #7
    Lieutenant Junior Grade marc c's Avatar
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Quote Originally Posted by sutor623 View Post
    Sure Marc. Well technically, it calls for 48:1 from the factory. It is a 1969 Johnson 4hp 2 cyl. These motors have one bearing in the crank case, so everyone with experience with them says it is better to run it at 24:1. Otherwise we have seen them run hot, or just blow up. BTW, she runs like a sewing machine......
    Cool, good to know.
    1974 Glastron V-179, Mercruiser 140
    1984 16.5ft. Alumarine Sealark side console with 82 Merc 50
    Homeport - Lac du Bonnet, MB, Canada
    I've used Fram oil filters in all my junk for 35 years-no problems

  8. #8
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    cr2k, then how come they say to run 25:1 for break in on some mtrs that after break in require 50:1 ??

  9. #9

    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Quote Originally Posted by JB View Post
    Using the 24:1 will not harm your Merc. You might need to clean your plugs and decarb your engine more often, but that is all.
    No , I don't agree with that...

    If you run a higher oil content you will be weakening the fuel/air ratio , this in turn will raise the cylinder temps as you will be
    running a lean mixture.
    Eventually if the mixture is too lean you will burn a hole in a piston or seize the engine as the cylinder temps get too hot.

    It is a myth that putting more oil in a 2 stroke helps the engine through better lubrication.

    Rich

  10. #10
    Captain jbjennings's Avatar
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    I would run the 25:1 if emergency, but wouldn't otherwise because I'd think it would eventually coke up the piston rings----probably not but it would worry me. I wonder how much the 25:1 would affect fuel viscosity and therefore lean the mixture...... I am no expert, but would like to see some data on how much it would actually lean it out.
    Not a certified mechanic but I have at least 2 shade trees in my yard and my wife always says I'm certifiable. So remember that when you follow my advice

  11. #11
    Cadet
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    I agree, will run lean. With a chain saw you would have to retune for that much oil change.

  12. #12
    Commander sutor623's Avatar
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Quote Originally Posted by JB View Post
    Using the 24:1 will not harm your Merc. You might need to clean your plugs and decarb your engine more often, but that is all.
    Sorry fellas, but I'm going to have to go with the Mod on this one. Highly doubt an experienced boater and Moderator would give me bad advice. But to each his own.

  13. #13
    Supreme Mariner
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Well spoken

  14. #14
    Master Chief Petty Officer
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Going from 50:1 to 25:1 means adding an additional 2.67 oz of oil to 128 oz of fuel. Sorry, guys, adding 2% more oil isn't gonna cause a lean burn in a properly tuned outboard engine, or else any engine recommending double oil during break-in would be in harm's way ...

  15. #15

    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    go for it dude.
    i've seen many 2 stroke motorbikes sieze and burn holes in the pistons because
    of a lean fuel/air ratio due to over oiling.

    I am not so experienced with outboards but personally I wouldn't risk it for long periods.

    Rich

  16. #16
    Commander sutor623's Avatar
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    Default Re: Can I run 25:1 oil mix when it calls for 50:1?

    Quote Originally Posted by fragged View Post
    go for it dude.
    i've seen many 2 stroke motorbikes sieze and burn holes in the pistons because
    of a lean fuel/air ratio due to over oiling.

    I am not so experienced with outboards but personally I wouldn't risk it for long periods.

    Rich
    Yeah well if a 45 year old engine still runs like this...... then I doubt a little extra oil is going to take her out.

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