I have a Mercury 2021 60HP Fourstroke and will be changing the oil (and lower unit) soon. Owners Manual says 25W-40 for use above 40F OR 10W-30 all temps. I have been using 25W-40 but considering changing to 10W-30. I have a quart of 25W-40 leftover from last fall. Can I mix it with 10W-30? It takes 3 quarts. OR should I just stick with the 25W-40?
Yes, mix away. Oil forums talk about this all the time. No problem, especially amongst same brand of oils.
If you are really changing the oil are you really mixing it?
If you are really changing the oil are you really mixing it?
Yeah why not
If you are really changing the oil are you really mixing it?
Mixing 1qt 25W-40 and 2qt 10W-30 in same crankcase.
<div class=”d4p-bbt-quote-title”>Ripjiggen wrote:</div>
If you are really changing the oil are you really mixing it?Mixing 1qt 25W-40 and 2qt 10W-30 in same crankcase.
Why not just keep the 25W-40 for next year, and run the 10W-30 this fall/winter?
You can buy 4 quarts of 10W-30 Marine oil for like $30. Why putz around with mixing oils at that point?
You will have 15w33
Had a similar existential oil crisis mixing dexos and non dexos in my last change in the truck.
Hasn’t blown up yet 
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