You MUST check your owner's manual to be absolutely certain of your engine type. The manual will specify the oil viscosity recommended by Chevrolet. However, that information can be outdated.
Generally speaking, for these engines, a high-quality 5W-30 or 10W-30 oil meeting the API certification SN Plus (or better, such as SP or SN+) is a good starting point. Using an oil that meets GM's dexos1 Gen 2 specification is also a safe bet.
Here's a breakdown to consider:
* Viscosity (5W-30 vs 10W-30): 5W-30 is generally preferred for better cold-weather performance. 10W-30 is a bit thicker and might be slightly better for higher temperatures or higher mileage engines, but 5W-30 is versatile and often recommended. Again, check your owner's manual.
* API Certification: The API certification (like SN Plus, SP, or SM) indicates the oil's performance standards. Newer certifications generally meet or exceed older ones.
* Synthetic vs. Conventional: Synthetic oils generally offer better performance and protection, especially at higher temperatures and under strenuous driving conditions. Conventional oils are more affordable but might not last as long. Many people successfully run conventional oil in these cars, especially if they change it frequently.
* Oil Brand: Many reputable brands make excellent oils. Mobil 1, Castrol, Valvoline, Pennzoil, and Royal Purple are popular choices. The brand itself is less important than meeting the correct specifications.
In short: Find your engine type, consult your owner's manual (for the original recommendation), and then choose a high-quality 5W-30 or 10W-30 oil that meets the API SN Plus (or better) and ideally, GM dexos1 Gen 2 specifications. If you're unsure, consulting a mechanic specializing in classic Corvettes is a wise decision. Using the wrong oil can damage your engine.
