What is better, straight weight oil or multi vis oil?

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  • What is better, straight weight oil or multi vis oil?

    I have always used straight weight SAE30 or SAE40 in all of my boats. The marina changed my oil last season and put in SAE10W30. I didn't notice they put in SAE10W30 until I happened to see the receipt. I can't tell the difference in the way the engine runs but I always thought that using straight weight oil is better because a marine engine works so much harder than a car engine. I have an older 1989 454CI engine w/ 855 hours. Is there a difference using straight weight oil -vs- multi vis oil? I don't have the manual for the engine so I don't know what the manufacturer recommends and it's not on the dip stick either. If straight weight is better should I be using SAE30 or SAE40? For what it's worth the straight weight SAE40 says "FOR HEAVY DUTY APPLICATIONS". I don't know if this means anything or not.

    Because I've always used straight weight oil I am thinking about draining the SAE10W30 the marina put in but if it's not going to make a difference I will leave it in for the season and go back to the SAE30 or SAE40 when I change the oil at the end of the season.

  • #2
    Best I can offer, but you’ll be fine
    ’19 Invincible 36 - 350 Verado’s Sold
    ’20 Invincible 35’ Cat, Quad Verado’s on order
    Fairhope & Orange Beach, AL


    • #3
      Honestly, pretty rare to see marine gas engines wear out from interior component wear due to hrs and breakdown of oil.
      You will be fine, it might clean it out a bit.
      Engine Sales and Service
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      • #4
        Nothing in writing but back in the 70's mutli weight was just becoming more prevalent around here. Besides the fact of operating under a range of weight classes depending on temp, it was said to have more/better detergents in it. It cost more of course(back then). Today, single weight oil usually cost more than multi weight.
        Small town S. W. Ga./St. James Fl.


        • #5
          Years ago multi-grade (not weight) oils were not as robust or durable as the viscosity improver additives would shear in heavy use and break down fairly quickly thus lessening the "thickness" of the oil and losing its shock load ability.

          In recent times the lubrication requirements have been improved due to smaller higher revving engines, reduced emissions engineering, the popularity of turbocharged engines, and longer drain intervals. What has improved for the auto industry has trickled down to the marine industry for the most part.

          Today's multi-grade oils hold up their viscosity better and with less shearing problems. The auto industry trend is for lesser viscosity oils as many cars are using 5W-20 and even 0W-20 lubricants. Soon you will see a another grade called OW-16. Compare marine engine oil requirements from a generation ago to current engines, you will find more multi-grade lubes than before.

          For the popular 4-stroke outboards, the NMMA has minimum requirements for their FC-W certification which is even a better step above car and truck oils, and almost all are multi-grade.