Should you use 10w40 engine oil in a 1968 V8 Mustang?

It is generally not recommended to use 10w40 engine oil in a 1968 V8 Mustang. The engines in these vehicles were originally designed to use a non-detergent oil, such as SAE 30 or SAE 40. These non-detergent oils have fewer additives than modern 10w40 engine oils, which helps to keep the engine cleaner. Additionally, the viscosity of 10w40 engine oil is too high for the engines in these vehicles, which can cause increased wear and tear on the engine components, especially when starting the car. It's best to use the manufacturer-recommended oil, which for a 1968 Mustang would be SAE 30 or SAE 40 non-detergent oil.