Well, I said that the oil type and viscosity would not matter but I did not mean that there would be no change. I said it badly the first time and not much better this time- perhaps I can explain.
The oil will leak out of the CCT (cam chain tensioner) no matter what viscosity that oil is, especially when the oil is warm. That said, thicker oil will leak more slowly than thinner oil, especially when it is cold. :-) So let's say that particular 5W-40 oil takes 12 hours to leak out of the CCT when the engine and oil are fully heated. Using a 15W-40 weight oil will slow that process so that it might take 18 hours to leak down. So the thicker oil will not prevent the start- up rattle but it will push it off to a later time and if you start the bike w/in the longer time period the rattle will not be there with the thicker oil. Also a thicker oil will come up to full pressure more quickly on start up so even if the rattle is there it might be noticeably shorter than when using the thin oil.
So oil type / weight is not a preventative or cure but it very well could change how and when the rattle appears. Still, I would not worry about it and would use any oil you are comfortable with, especially if that oil is w/in or close to the parameters specified by Kawasaki. If thicker oil calms the start- up rattle and you like that, then by all means continue to use that oil just for that reason. (seriously, not sarcastically)
Brian
Ya, I was wondering if 5x40 oil viscosity was too thin when cold and might cause the rattle in my 08.
guess I'll live with it, tho it didn't seem to rattle when I used 15X40 Rotella
maybe my imagination