Quote:
Originally Posted by kkim
why are you using a 50wt oil?
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I'm no oil expert, but I looked into this before making a decision. I would love to get contrary opinions, but there were a few reasons I went with 20/50. First is that it may be too early for synthetic. I'm only at 600 miles on this bike, and while there is debate, I thought I'd play it safe and wait a bit longer using conventional oil. If I'd gone synthetic, I wouldn't have any worries about a 40 weight oil.
But habit has me hesitant about a conventional 40 weight oils. I'm used to running 15/50 or 15/40 deisel oil in motorcycles, because of the higher film strength and the fact that if you use auto oil (like I did in my last bike) 10/40 and 30 weights often have friction modifyers that make the clutch slip. Not directly applicable since I'm using a motorcycle oil this time, but there is some discussion of this in
this article by Mike Guillory, a motorcyclist and oil chemist.
Guillory does specifically recommend a 20/50 for warmer weather, " 20w50 is better in warm weather than 10w40, because it gives you a thicker oil cushion between bearing surfaces at operating temperature." It never gets below 75 degrees here, and a 20/50 is rated down to 32 degrees, so I'm fine on the bottom end. It does get up over 100 degrees though, so there is a chance the 10/40 wouldn't cut it during summer. 20/50 is within the ranges recommended by the manual for the weather.
And non-synthetic 40 weight has other problems, too. As discussed in
this great article on oil by Mark Lawrence, 10/40 is one of the more unstable oils, so it breaks down more quickly, losing top end capabilities. In one study, after only a few thousand motorcycle miles, 10/40 effectively became 10/25. This has me worried about the hot Caribbean summer, especially because my bike will have a couple thousand extra miles on it just when summer hits.
Finally is the very practical reason. Perhaps because of the local weather, 20/50 is the only weight of motorcycle oil local stores carry. They did have the good heavy duty non-synthetic deisel oil I've used before (Rotella 15/40), but it was more expensive than the moto specific oil, so I stuck with the moto-specific 20/50.
What concerns do you have? I certainly respect your opinion and would love to hear any concerns. It's a fascinating topic.