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  1. #1
    Commander Expidia's Avatar
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    Default Best oil 4 40 hp merc 4 stroke?

    Not to start the old oil debate but . . .

    For the purist's out here (which I am one) I have only used the Merc blend in in the Quick Silver gallon jug.
    I figured I'd give my O/B a mid season treat last week and changed the oil. I only had a little left of the Merc blend so I used a jug of 10w-30 Pensoil I had in the garage.

    Now that I look at the almost empty Merc jug it says 25w-40 for Sterndrive and inboard motors.

    A check of my manual calls for their Merc 25w-40 synthetic blend. The jug I had is not synthetic.
    The manual also says if you prefer to not use synthetic, Then the Merc 10w-30 blend os OK or another good quality approved 10w-30 oil (which is what I used)

    Anyone think after 5 years I could switch to using a synthetic blend Merc or other 25w-40 synthetic and also change the filter at the same time too so as not to mix oils.

    I usually change the 3 plugs oil, filter and lower unit oil at the start of the season.

    Should I just stay with a good quality 10-30 and would changing to synthetic be overkill and something Merc would love to see everyone buying their synthetic oil only from them!

    I clock about 200 hours a season over maybe 6-7 months.

  2. #2
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    Default Re: Best oil 4 40 hp merc 4 stroke?

    Most 4 cycle marine engines recommend FC-W oil. I would stick with that. Automotive oil is not usually FC-W, and therefore not recommended. I do not think the synthetic vs non-synthetic is the proper question.

  3. #3
    Commander Expidia's Avatar
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    Default Re: Best oil 4 40 hp merc 4 stroke?

    Quote Originally Posted by Chris1956 View Post
    Most 4 cycle marine engines recommend FC-W oil. I would stick with that. Automotive oil is not usually FC-W, and therefore not recommended. I do not think the synthetic vs non-synthetic is the proper question.
    The jug I used was actually Quaker State 10w-30.

    The specs on the Mercury jug are: Premium SAE 25W-40 blended with special high grade oils and formulated without viscosity improvers, giving a premium quality multi-viscosity 4-cycle motor oil. Suitable for use in gasoline or diesel sterndrive and inboard engines. Meets API service SJ, CF-2, CH-4. SAE 25W-40 1-gallon / 3.785L

    Notice it does not say 4 stroke outboards though? I'll pick up some Marine Grade as you suggest.

    But one of my original questions was "my merc manual" says use 25w-40 synthetic. I avoided the synthetics when O/B was new as a gal is like $62 against the Merc 10w-30 for around $30 a gal. as Merc's 2nd recomendation.

    Could you expand on why you say syntehtics is not the proper question???

    I was under the impression that once you run regular oil in an engine you should not switch to a synthetic . . . is this why you said that?

    Thanks for your input.

  4. #4
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    Default Re: Best oil 4 40 hp merc 4 stroke?

    No, What I meant was that you should run FC-W oil. I think it less important if it is synthetic or non-synthetic. Is that QS oil FC-W? I will bet the Mercury oil is....

  5. #5
    Commander Expidia's Avatar
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    Default Re: Best oil 4 40 hp merc 4 stroke?

    The QS oil has no lettering to that effect. It's bottled for Walmart as I see their name on the oil. Need to get that stuff out. Who knows, probably recycled stuff. Thx for that response.

  6. #6
    Petty Officer 2nd Class catfish58's Avatar
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    Default Re: Best oil 4 40 hp merc 4 stroke?

    I have a 2006 75 hp merc 4 stroke. I use Quicksilver 25w40. That is what the dealers mechanic told me to use. It is also on the sticker by the oil fill. I plan on keeping this outboard 'forever' and since I just change the oil once a year the extra cost is worth it if only for piece of mind.

  7. #7
    Commander Expidia's Avatar
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    Default Re: Best oil 4 40 hp merc 4 stroke?

    Update: thanks Catfish. I actually ordered a gal of the Mercury Quicksilver 10w-30. The last gal I had before I ran out was Mercury Quicksilver formulated for inboards and out drives! I doubt that there is a difference between quicksilver inboard or the outboard formulation anyway, but when I ran out I had used some Quaker State automotive 10w-30 that had Walmart on the label too. It's probably recycled stuff and it's for automotive use anyway. From what I've read Marine grade oil has additives to reduce moisture so I wanted to get that stuff out of there anyway and use what Chris poster above and my Merc manual recommended anyway. At least this Mercury Quicksilver 10w-30 is formulated for 4 Stroke "outboard" performance.

    Gotta love the web. Several days ago I had no desire to start driving around from store to store to find a gallon. I knew West or a marina would be like $30 and I bought the wrong oil from West them the last time. No point in driving to a Walmart as they are usually out of stock by this time of year. Their boating aisle is probably Xmas decorations by now

    So I searched online and it was not easy as most sites were $30 plus shipping. Some even had $12 shipping Hahaha. But I finally found a boating store online for $19.99 with free shipping. Amazing, 3 days later today it was sitting on my doorstep. Funny thing though, still has no markings as to FC-W on the bottle anywhere. They probably get away with that by just saying specially engineered for 4 stroke marine use!

    Going out to change the filter and oil right now. I'll save the other stuff I put in two weeks ago to top off my cars.

    I know oil discussions threads can start a war and any good grade marine oil (as the manual says) will suffice. But from my experience, keeping track of each service in those blank pages in the manual, noting what brands you used for each service and keeping all receipts . . . I keep my toys pristine. When I go to upgrade and the buyer looks at the care and maintenance my item has had. Usually, the first buyer grabs it and I usually get a premium price which pays for the extra cost of using name brand products along with peace of mind while I had the use of the item.

    Thanks for all the above responses.

  8. #8
    Petty Officer 2nd Class catfish58's Avatar
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    Default Re: Best oil 4 40 hp merc 4 stroke?

    I just pick up a quart at a time while i'm at wally world for other stuff. When it's time to change oil I have everything on hand and it doesn't break the bank.

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