* Check your owner's manual: While generally safe, it's always best to verify if Ford specifically recommended synthetic oil for that model year. Some older manuals might only specify conventional oil. If it doesn't explicitly prohibit synthetic, it's usually fine to use.
* Oil viscosity: Make sure you use the correct oil viscosity grade. Your owner's manual will specify the recommended weight (e.g., 5W-30, 10W-30). Using the wrong viscosity can damage your engine.
* Initial oil change: When switching from conventional to synthetic, it's good practice to change the oil and filter a little sooner than your usual interval to ensure a thorough flush. This isn't strictly necessary, but it's a precaution some prefer.
* Potential for leaks: In older vehicles, synthetic oil can sometimes reveal minor leaks that weren't apparent with conventional oil because it's a thinner fluid. It's not a common issue, but keep an eye out.
In short, switching to synthetic oil is generally acceptable and often beneficial (better performance at high and low temperatures, longer drain intervals) for a 1997 F-150, but always double-check your owner's manual for specific recommendations and use the correct viscosity.
