My uncle has a 1992 full-size Chevy Silverado pick-up truck. It has a V8 diesel engine with a turbo (I'm not sure of the exact engine size).
He put in a new engine about a year ago, and he just installed a brand-new turbo, after his rebuilt one went up. He occasionally uses the truck for towing a trailer, but not often.
I would like to know...
Which oil brand is the best conventional oil?
AND
Which oil brand is the best synthetic oil?
... to use in such a vehicle, especially to help keep the turbo running well.
Thanks in advance!