* Check the engine: Identify the specific engine (e.g., 5.7L V8, 4.3L V6, etc.). This information is usually found on a sticker under the hood or on the driver's side doorjamb. Knowing the engine is crucial for selecting the correct oil.
* Oil type: For an older vehicle like a 1989 Silverado, a conventional oil is often sufficient. However, if you want better performance and protection, you could consider a high-mileage oil formulated for older engines. Avoid synthetic oil unless specifically recommended in your owner's manual, as it might not be compatible with all older engine seals.
* Viscosity: The viscosity (weight) of the oil is crucial. This is usually indicated by a number like 10W-30, 10W-40, or 20W-50. The owner's manual will specify the recommended viscosity grades. In general, higher numbers (like 40 or 50) are better for hotter climates or high-performance driving, while lower numbers (like 10 or 20) are better for colder climates. A common choice for older trucks is 10W-30 or 10W-40, but always check your manual.
* API certification: Look for the API (American Petroleum Institute) certification symbol on the oil bottle. This indicates that the oil meets certain quality standards. For older vehicles, you'll likely find an "SF," "SG," or similar designation. Modern oils often have a more recent designation, like "SN Plus". While a newer designation might offer better performance, it's generally safe to use an oil that meets the older standard recommended for your truck.
In summary: Find your owner's manual to determine the exact type and viscosity of oil recommended. If you can't find the manual, take the engine information to an auto parts store. They can help you select the appropriate oil for your 1989 Chevy Silverado.
