where is the old going

I have a 1982 (I think) 446 case.

it run ok and mows ok. but it uses some oil,

If I pull it hard and mow most of my big yard is will lower the oil about 1/2 the marks on the dip stick, which is not too bad. But I always check it before and after I mow.

because after a couple of mowing without adding oil, it would be out of oil

I do not see any oil smoke while mowing. have seen some smoke at startup.
a few times.

I use shell rotella 30 weight oil

any ideas, should I change the type oil I am using??????????