5W40 synth is a real bargain/gallon at Walmart. Since I use it in other machines, I could get the economy of scale when I change the oil (Which I tend to do frequently) I know Polaris recommends their 0W40 but I think I read here that some use Castrol 5W50 syntec with great success in engine and tranny. Polaris oil has evolved from 0W40 to 0W50 and now I'm jhear 2W50.......5W40 would seem to be ok if not used in sub 0 temps.

 

I used 5W40 in my 81 and 87 Mercedes Diesels but never a atv, I would think it would work fine.

 

If Shell made their Rotella T Synthetic in 0W-40, I'd use it for sure. I'm sure the 5W-40 would be fine except like you said in sub zero temps.