I maintain a 2005 JD 4115 25hp Yanmar powered tractor at my workplace with about 1200 hours on it. The recommended OCI is 200 hours using 5w30
, 10w30, or 15w40. JD's oil grade recommendations never made sense to me. I change it once a year at about 90 hours because it has a really small sump - only 2.1 quarts vs. my old Kubota with 4+ quart sump.
When new, I debated 10w30 vs. 15w40, maybe running the 10w in winter and the 15w in the summer (very short OCI). The dealer, for what it's worth, recommended running the 15w40 year round,especially emphasizing it for summer.
That's what I've been doing and everything is fine. The tractor sits in an attached unheated garage (tempers the cold a bit) during winter when I use it for snow plowing. It starts just fine in the winter, but I'm sure that it is not the best option the very few times it is started below 10F. My old Kubota recommended 10w30 year round.
If I used this tractor a lot of hours, I would consider managing the oil better. My point is, at my low hours accumulation, I will never notice that extra bit of engine wear that occurs on 3 or 4 cold start ups per year. One would think that 5w40 would be the best for a year round oil if you are on the fence about choosing. I know Dnewton is impressed with HDEO 10w30s and maybe that would work as well - the dealer thought it might not be wise under very heavy, hot summer use.
I'm in central lower Michigan.