<snip>Should I switch to 5W40 oil?
Or use 10 W60 again
10W60 or 5W40 for my XT 2009?
How about neither of the above?
I looked through this thread but could not find an obvious answer: Why not simply follow the manufacturer's recommendation (which is probably 5w30)? Are you experiencing some kind of problem with 5w30? If it ain't broke, don't fix it ;-)
That said, when using 5w30 you might monitor your oil usage very carefully. How much oil are you really using? If 1 quart per oil change, consider yourself lucky. If you are using more oil - using more than you prefer - then consider the following. When a vehicle is using oil, the easiest and cheapest solution is . . . simply add more oil.
You might also experiment with oil brands - Castrol Syntech might hold up a bit better than, say, Mobil-1.
You might also try a 0w30 rather than 5w30. If that sound counter intuitive, the reason it matters is this. Synthetic oils consist of a base stock plus additives and viscosity index modifies. Even within a single brand of oil (say Mobil-1), the base stock for 0w30 is probably different than the base stock for 5w30 . . . different as in 'better' or 'more robust'.
You might also experiment with the oil change interval. In North America, it's still 3,000 miles. From my experience with Mobil-1, there is little or no usage in the first 1000 miles; a bit more in the second 1000 miles and most of the usage occurs in the last 1000 miles. Watch this carefully. It's pretty clear to me that Mobil-1 starts out great, but starts degenerating as the oil change interval progresses.
You might add an air/oil separator. You are assuming that the oil is passing the rings, but it might be escaping through the PCV valve or breather.
Finally, if you're really adventuresome, you might try an oil additive like boron or MoS2. On my present 2012 FXT with 103k miles and a Grimmspeed AOS, I'm using Mobil-1 5w30 with MoS2 added. I can go 5000 miles and not use any oil - zero, nada, zip. I was able to do this same thing on an 2006 FXT which had 160k miles when I sold it - zero oil usage. Aside from bragging rights, the zero oil usage and extended OCI more than paid for the MoS2. I could extend the OCI beyond 5000 miles, but at some point the small oil filter would need changing.
p.s. Personally, I would avoid using a heavier oil unless you have exhausted all other options. As
@Scooby24 stated 'Tolerances were not designed for a 60 weight oil.' IMHO, the tolerances were not designed for 50 weight either - maybe 40 weight as well. Heavier oils will make your engine less efficient and reduce cold start lubrication. There are several better options available.
The 2006 . . .
and the '12