You MUST check your owner's manual. This is the definitive source for the recommended oil weight and type.
However, in the absence of the owner's manual, here's some general guidance:
* Most common recommendation: For older engines like those found in a 1969 F100, a straight weight oil like 20W or 30W was common, especially in warmer climates. A multi-grade oil like 10W-30 or 10W-40 is generally considered suitable for most conditions and is likely what's recommended for many of these engines today. Higher viscosity weights (like 40W or 50W) might be needed in exceptionally hot climates.
* Consider the engine: A larger displacement engine might benefit from a heavier weight oil than a smaller one.
* Climate: Colder climates generally require a lower viscosity oil (the "W" number), allowing for easier starting in cold temperatures. Warmer climates can use a higher viscosity oil.
* Modern oils: Modern oils often exceed the standards of those used in 1969. You can likely use a modern multi-grade oil that meets the API standards appropriate for your engine, though a straight weight oil is also a possibility.
To find the correct oil, you need to:
1. Identify your engine: Look for an engine tag on the engine block. This will tell you the exact engine type (e.g., 240 inline-6, 302 V8, 390 V8, etc.).
2. Consult a repair manual specific to your engine: Chilton's or Haynes repair manuals often provide details on recommended oil weight.
3. Check online resources: Websites specializing in classic Ford trucks might offer guidance based on your specific engine.
Using the wrong oil weight can seriously damage your engine, so please prioritize finding the correct information for your vehicle.
