I use Mobil 1 10W-30. I think 5W-30 is just fine. Around here we don't have extreme hot or cold so we can easy run the same weight oil all year. Moderate range is sufficient. I was originally running 15W-50 per a local's recommendation but I think there's no need to run heavier weight oil that robs horsepower. But it does help reduce the leaks.
15-50 Mobil one
Ive always used it and have good luck with it..
I talked to old Ohio George and he swears it was the best oil he ever used while maintaining 80 yes 80 Buick v6 indy lite engines . . He swears he used all the oils out there and would take all the engines appart after every season and Mobil one was the only oil that the bearings would show little to no wear after a season of racing.He has worked on more stage 2 buicks than ANYONE (Dan at pte or Bill Anderson,Rob at RPE)and i mean ANYONE. The guy has seen it all as far as Buicks go because he was in charge of the whole engine program for the indy lites. He told me when he started the progam he spent over 1 million dallors of Buicks money in engine parts. He bought all 80 of them back after Buick pulled out and had them stored in a warehouse for years for pennys on the dollarHe has more stage 2 motors than anyone on the planet