The 1,000,000th question about oil on here.

[yullose]

The first year GM started using synthetic was the first year they put the LT1 in the Vettes. I'm pretty sure that was '92 or so. Hadn't seen it before then.

FWIW, I run Castrol 20/50 in my '86 T-type.

 

[Weazel]

I run a Valvoline Synthetic blend, it's like $2.50 a quart so it's easier to swallow than full synthetic. Plus I'd also read about the leaks with full synthetic, and with my rear main seal weeping oil as it is, I'd hate to exacerbate that situation. But yes, there will be as many opinions as types of oil. The car wanted 10-30 from the factory. With the engine being looser now, I run a 10-40. I just think 20-50 is too thick, considering the climate up in Maine (it can be below freezing well before the roads are salted and the GN goes into hibernation, haha). Best of luck.