BillDurant

My Son and I are about to change out oil & filter & antifreeze
1989 117,000 miles 6 speed manual
Oil was changed out last year by local garage.

My son suggests Synthetic Oil ? Any thoughts?
If so what brand & type ?
and preferences on Antifreeze? for older car bit of miles
car does run great tho
Thanks

Eilias

Starting with the LT1 factory fill was a Mobil 1 synthetic. They didn't have oil coolers equipped, and the synthetic could take the high heat with no issues. On an L98 conventional shouldn't give you any issues, especially if you aren't racing it or running it hard.
Changing it regularly is more important than a synthetic is.

For antifreeze, the old style green stuff should be what is in your car. Changing it is always a good idea if you don't know the condition of it.
DO NOT MIX GREEN WITH DEXCOOL!
It should be as simple as removing the radiator petcock and the knock sensor on the block, then refilling and burping the system. On my LT1 it took maybe an hour for the whole process.

RetroGuy

The oil change should go fine with synthetic Mobil 1 5-30W or 10-30W and a new Mobil 1 filter or a Fram synthetic filter. The coolant system is a lot more messy. You need to not only drain the radiator, but also the overflow tank. You should also fill again with water and flush the system prior filling with new Dexcool. You can find intstructions on this forum. A complete proper coolant change can be a lot of hassle unless you have a type of pro lift or kwiklift. I took mine to a pro radiator shop for its coolant needs.