'70 Cutlass Rocket 350, 111k miles, Northeast area. I try to drive it at least once per week maybe two, if not then I try to at least let it run for 10 min. Until I can get to fixing a minor leak I need top it off every so often.. 10/40 or 30, Synthetic or not? Thanks!

 

You will find that opinions on this vary widely. If you check older threads (and there are allot of them), I don't think that you will find any definitive answer. But since you asked...


For my '71 Cutlass Supreme 'vert with a 350 4bbl...Pennzoil High Mileage 10W-30. Even though I only put about 1500 miles on her a year, I change the oil every spring when I pull her out of storage. I've been using Pennzoil for over 30 years and never had an issue with any of my cars.


And now lets hear from the Quaker State and Castrol contingent.

 

in my 2003 marauder i run 5w-20 ( i think) mobile 1

i run 10w 30 in my 83 hurst olds, not tied to any one brand of conventional oil

in my fresh rebuilt 350 rocket i run 10w-30 brad penn on the recomendation of the engine builder.

in my 87 cutlass sedan i run 20w 50 because it burns oil and that weight slowed down the rate i was having to add.

Im switching my 70 GS stage 1 to brad penn because of the zinc content.

 

- Eric

 

The synthetic will leak where dino juice didn't. Thats the only disadvantage. If you already have a leak it will worsen with the synthetic.
I run Shell Rotella T 15/40 or 10/40 in my old school engines. New school gets Mobil 1. Both get a can of Prolong.

 

What droldsmorland said!

 

What's the deal with the Prolong other than the name saying it all?

 

With the parameters you provided, on Long Island, I'd probably choose the non-synthetic 10W-40 in a reputable brand. If the engine has the flat tappets try to get a brand that has sufficient ZDDP additive. There has been a tendency to significantly reduce it, and the cam & tappets would appreciate it being there.

 

Put it in your Googler. I've been using it for years. Its an oil additive which treats the metal and bearing surfaces, it does not treat the oil. Ive disassembled many engines with many hours (Prime Power Generators) on them and the lack of wear always amazes me. I put it in every IC engine I own.