I did a bit of looking around and the C175 should have the Kohler KT-17.
I also found a manual for the KT-17, and Kohler recommends straight 30W oil for temperatures of 32* and above.
I also found the B & C Series Wheel Horse Owners manual. In it they call for a "Premium quality motor oil with a viscosity of 10W-30 or 10W-40".
Personally, I would recommend following the Mfg. recommendation. That's what I do with my old GTs and it's worked for me.
I'm a "Bolens Guy" and don't know that much about the Wheel Horse tractors. However there are a lot of really good knowledgeable Wheel Horse guys at this forum:http://gardentractortalk.com/forums/forum/20-wheel-horse-toro/
The guys at GTTalk are like most of the folks here, a right friendly bunch and willing to help you with any questions you have. This post was edited by OldBuzzard at 14:04:07 06/04/13.