what weight oil/ what kind

I have a yz400f 1998, I bought 4 quarts of motorcycle oil, 15w 50 because i found it on sale and i was planning on using it until somebody told me it needs to be like 90 degrees f to use or its to thick so i am wondering if i should use it or not it is around 50 degrees in wi right now i am currently running 5w 30 last summer i ran 10w 40 so what should i be using and what is the weather i should be using these in 

Depends on the bike, but I pretty much use 20W50 year round.

Attached is a typical oil range chart from the manual.  Note that 20w-(X) is good for temperatures down to as low as 50 ℉.  10w-(X) covers temps as low as 10 ℉.  On the up side, (X)w-40 is usable in weather up to 110 ℉, so there is rarely a reason to run 50 weight oils at all, although I personally use a 20w-50 during the hottest 3 months of the year in SoCal (July-Sep) when temperatures are at or above 90 ℉ most of the time.


50 weights are unnecessary in cooler weather, and I almost always run 40's because the lighter oil circulates faster, and the volume of oil delivered to the lube points is more important than how thick it is. 


Use a premium oil, preferably a true full synthetic blended for use in motorcycle engines that share engine oil with the clutch and transmission.  Change or service the filter every time you change the oil.


ok thanks it rarely gets 90 in wisconsin so I will stick rotella t6 10w-40 

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