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What weight oil to use????

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briang0

Regular Contributor
I just bought a new boat switched from Crusader to Mercruiser the engine is a 83 305. The tag on the engine says to use straight 30 weight. The service manual for the engine says to use 25w 40. Does it really matter if I do not use a multiweight oil. I only use the boat from May to early October the weather never gets below the upper 40's. In my older Crusader engine I only used 30 weight oil and never had a problem I'm thinking it should be the same for this engine.
 
25W40 is Merc's current recommended oil. You are in a cool climate so 10W30 or 10W40 would work. Straight 30 would not hurt it one bit.
 
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