As far as I understand you have to change oil every year if the bike is stored during the winter. The used oil that sits in your sump breaks down and forms corrosive byproducts (vapours). If the bike is being used continually these vapours don't have the chance to corrode the insides of your engine. If the bike does sit too long between rides or during the winter months (we're talking months) then these byproducts will cause corrosion and damage the internals. This is definitely true for mineral based oils. I'm not sure if it holds true for synthetic oils as are used in the XR.
Therefore, change at the END of each season. Guys please comment if I have been misled all these years.
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