My Wolverine owners manual calls for 10W30, but most ATV oils sold are 10W40? Can I uses 10W40 and will its hurt the motor?

 

No, it will not hurt it. If I was you I would run 10W-30 in the winter, and 20W-40 in the summer.

 

Whats the diff between 10W30 and 10W40?

 

10-W40 is a little thicker than 10-W30. Thats why you run thicker oil in the summer and thinner oil in the winter. The viscosity (basically the buildup of the oil) thins out when it heats up (basically the warmer the oil gets, the thinner it becomes). In the winter, the oil will not get quite as hot as it would in the summer (unless u live in the desert, cali or florida where its always warm), so you can run thinner oil. But if you ride alot and its hot outside (80F or higher) i'd use 10-W40.

 

I run 15W-40 in mine year round. Rotella, best ever.

~HoundDog

 

The base stock, is 10 weight for each oil, then they add viscosity improvers, to get the 30 or 40 weight for hot. The 40 weight has much more improvers than the 30 does. My yamaha owners manual doesnt suggest 10w 40 ever. It does suggest 20w 40 for very hot weather, this is 20 wieght oil with improvers for hitting 40 weight.
The bigger the spread, between the lower number and the higher number, means more improvers. This is why they only recommend 10w 30 or 20 w 40.
Heres some links to more info about oil.

oil links

 

I use Yamalube semi synthetic 10/30 with a 20% addition of Lucas synthetic additive....The thinner the oil..the easier it pumps at higher r.p.m. and I change mine every third or fourth ride...no matter what.Motorcycles are just harder on oils.

 

Try Amsoil 4 stroke 0 W 40 full synthetic. My Big Bear loves it, and it runs noticably cooler as well. Can be run all year round.