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This topic ignites such a firestorm on all the other motorcycle sites. Glad it didn't happen here. I use Shell Rotella "T" 15w40 Jaso MA spec (about $13.00 per gallon at Walmart). I once tried Valvoline "Motorcycle 15w40" for only about 200 miles and drained it out to go back to Rotella. With the Valvoline the shifting was noticeably less smooth and noisier from the very beginning. Hated absolutely every minute the Valvoline was in there. Well over 27,000 miles with the Rotella now and NO issues. At 3,000 mile drain intervals it still looks clean enough to re-use in the car.

Joe

In hindsight that makes sense. I used 5W-40 mobile 1 and my shifting feels "crunchy" but not in a bad way, just more noticeable. That Rotella is great stuff! I just can't justify the extra expense when I change my oil every 3k. I usually use the "high mileage" or the stuff with the diesel rating since they tend to have more zinc. I also would think the thicker 15W40 would hurt fuel economy. From what it sounds like you've gotten fuel economy wise it sounds like a false assumption on my part.

It does get cold here in the Phoenix winters but not long enough or cold enough to require a 5w oil. In an engine this small conventional wisdom would say a lighter weight oil would indeed give better mileage though. I don't dare try it in summer when we seem to spend most of the year at 110+ degrees. Hmmm, maybe the heavier oil is why my gas mileage drops in winter even though the air is cooler and denser when cold. THAT in itself should always give better mileage and performance. I'll try dropping to a 10w30 this winter and see what happens to gas mileage.

Joe

according to my shop manual 10W30 is approved for use in the 500 up to 86F