Back in the day you could get Castol in a 10w50 but it was almost double a 20w50. I loved that oil but most didn't because they didn't want to pay a buck seventy five a quart!
BTW, Torco makes a 20w60 full synthetic. It's designed for some European engine IIRC. I almost used it and then said screw it and closed up my clearances so I can run 5w30 or maybe even 0w20. It expensive. $23.00 per quart.
