What grade motor oil for 1965 ford mustang with over 175000 miles?

For a 1965 Ford Mustang with over 175000 miles, you should use a multi-grade oil with a higher viscosity rating than what was originally recommended. The original recommendation was likely a straight-weight oil like 20W or SAE 30. However, due to the high mileage, the engine likely has more wear, requiring a thicker oil to maintain adequate lubrication and pressure.

A good choice would be 10W-30 or 10W-40. These multi-grade oils offer good protection across a range of temperatures and provide a thicker film at higher operating temperatures, compensating for wear.

However, always check your owner's manual. While the original recommendations might be outdated, the manual could offer guidance on appropriate oil for higher mileage engines. Also, consider the climate where you live – if you experience extremely hot or cold temperatures, you might want to adjust the viscosity accordingly. For example, a 20W-50 might be suitable for extremely hot climates.

Finally, ensure you use an oil that meets the API service specifications for your engine. This information will also be found in your owner's manual or on the oil bottle.