Considering the age and technology of the engine: Your 305 is a relatively high-mileage engine by now, so focusing on protection against wear and tear is key. It's not likely to benefit from the latest, most advanced synthetic oils in the same way a modern engine would.
Oil Type Recommendations:
* Conventional Oil: A good quality 10W-30 conventional oil is a perfectly acceptable and cost-effective choice for this engine, especially if it's primarily used for shorter trips or in moderate climates. Check your owner's manual; it likely specified 10W-30 back in the day.
* High-Mileage Oil: Consider a high-mileage conventional or synthetic blend oil. These oils often contain additives that help to reduce leaks and improve seal condition – beneficial in older engines. Look for a 10W-30 high-mileage formulation.
* Synthetic Blend Oil: A 10W-30 synthetic blend offers a balance between performance and price. It provides better protection than conventional oil, particularly in extreme temperatures or under heavy loads, but it's not as expensive as full synthetic.
* Full Synthetic Oil: While full synthetic oil offers the best protection and performance, the incremental benefit compared to a high-mileage blend might not justify the higher cost for a 30-year-old engine. However, if you consistently drive long distances or in demanding conditions, it could be worth it.
Viscosity (Weight): 10W-30 is a very good starting point. If you experience issues starting the engine in cold weather (thick oil), consider switching to a 5W-30. However, if you're regularly towing or driving at high temperatures, a 15W-40 might be better. Again, check your owner's manual for recommendations.
Oil Certifications: Look for oils that meet or exceed the API certification for your engine. You'll likely see "SM" or "SN" (older standards) on the oil container. Newer designations like "SP" or "SN Plus" will also work fine, offering additional protection, but may not be necessary.
In summary: A high-mileage 10W-30 conventional or synthetic blend oil is likely the best balance of cost, protection, and performance for your 1985 El Camino 305 V8. Always consult your owner's manual for specific recommendations. Regular oil changes (every 3,000-5,000 miles, or as recommended by your chosen oil) are crucial for maintaining your engine's health.
