Generally, for a 1969 Pontiac 400:
* SAE 10W-30 is a good all-around choice for most climates and driving conditions. This was likely a common recommendation from the factory.
* SAE 20W-50 might be preferred in hotter climates or for higher-performance applications or older engines with more wear. This thicker oil provides better protection at high temperatures.
* SAE 10W-40 is another suitable option, offering a balance between the two.
Important Considerations:
* Climate: Thinner oil (like 10W-30) is better for cold weather starting, while thicker oil (like 20W-50) is better for hot weather protection.
* Engine Condition: If your engine has significant wear, a slightly thicker oil might be beneficial to help compensate for the increased clearances.
* Owner's Manual: Always consult your original owner's manual if you have it. It will have the most accurate and specific recommendations for your particular engine.
* Modern Oil Technology: Modern oils are significantly better than those available in 1969. While the SAE viscosity is important, consider using a high-quality multi-grade oil that meets or exceeds the specifications for your engine. Look for oils that meet or exceed the API service classifications recommended for your engine.
In summary, while 10W-30 is a safe and generally accepted choice, determining the *best* viscosity for your specific situation requires considering the factors above. Checking your owner's manual is crucial. If you don't have it, you may be able to find a digital copy online.
