You really need to do a complete oil change at winterization. You need to run the engine for a few minutes with the clean fresh oil to flush out the old from the bearings, rings, lifters, etc. Used oil is acidic, but it's the soft metals that are damaged the most, and simply draining the old oil leaves the used in these areas so you really aren't helping. With an oil change in the fall, no need to do it again in the spring $.02
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