85 Monte Carlo

[Ace85]

Is it best to use synthetic oil? Should I use 97 octane gas? 305 with 66,000 miles.

 

[69hurstolds]

Today's synthetic oils shouldn't hurt. You could even go with snythetic blends to save a few dollars. It's more important to use either 5W-30 or 10W-30 quality oil and change it at recommended service intervals. The 97 octane isn't worth the money, IMO. You have a relatively low-compression engine that wouldn't benefit from the higher octane like some of today's high-compression engines. I'd stick with 87 octane NON-ethanol gas if you can get it without ethanol. Still cheaper than 97 octane, but has no ethanol in it which could be bad long-term in your vehicle.

 

[Sweet_Johnny]

Be sure to use an additive containing ZDDP if not using oil specifically designed for older engines. Synthetic/ conventional is up for debate but it's a good idea to pick one and stick with it.