It does have a gauge. Not sure how accurate it is, or if it works. It is mostly used to give my kids and my nephews rides. It was purchased new by my grandfather and has lived with me since he passed. Mostly a family heirloom that has many memories attached to it. It earned it's keep, and is now out to pasture.
My thinking was that 10w30 might be a good compramise for the obsolete 20-20w and that since it doesn't get up to temprature and stay there very often that a 30w might not be so great. It is old however, and having never been rebuilt, i'm sure the tolerances aren't really tight. Maybe a 30w or an even heavier 15w40 HDEO would work. I have engines that call for 30W, 15w40, 5w30, and 20w50, so some streamlining to buy in gallons would be good. Prices aren't all that much diferent from what I can tell, so that isn't much of a concern. This tractor doesn't see enough hours to require changing that often either.