However, since you don't have the manual, a good starting point for a general guideline is 10W-30. This is a common and fairly versatile grade that worked well in many vehicles of that era.
Crucially, you should consider these factors:
* Climate: In hotter climates, a higher viscosity oil like 20W-40 might be beneficial. In colder climates, a lower viscosity oil like 5W-30 might be better for easier starting.
* Engine type: Different engines have different oil recommendations. A big-block V8 will likely have different needs than a smaller inline-6.
* Oil type: Check whether the owner's manual specified straight-weight oil (like 30 weight) or multi-grade oil (like 10W-30). Modern multi-grade oils are almost always preferred. Make sure you use an oil that meets the API requirements that would have been applicable in 1982 (these requirements have evolved over the years).
Without knowing the specific engine, 10W-30 is a reasonable guess, but it's not a guarantee. If possible, find a 1982 Chevy Silverado owner's manual online (many are available as PDFs) or contact a Chevy parts dealer to verify the correct grade based on your truck's engine. Using the incorrect oil can harm your engine.
