Your timing is amazing. I was in Orielly's this afternoon, and another gentleman was there. He told the employees there he needed hydraulic fluid. When they asked what kind he needed, he said it was for his mower, and it called for 20W-50. The lady working there walked over to the 5-gallon pails of hydraulic fluid to check. Trying to be helpful, I went with her, and we checked the different pails there. "20W-50," I said, "That's motor oil viscosity, not hydraulic oil."
Went back to the gentleman, and asked if he was looking for engine oil or hydraulic oil. He said it was not for the engine, but for the reservoir on the mower, and that it had 20W-50 stamped right there on the side of it, next to where it was put in. He pulled out a piece of paper, and he had written it down from the manual. 20W-50 calling for CD spec. He said it was for a zero turn mower.
When he asked what he should do, the lady told him to check in the manual and see if they called for synthetic oil or not.
I asked what 20W-50 oil they had that was synthetic, and she said the motorcycle oil. I looked at her and said you think the manufacturer wants to use motorcycle oil in their mowers? She said the synthetic would handle the high heat.