Final answer:
If an oil's viscosity is too low at normal engine operating temperatures, it cannot provide sufficient lubrication, leading to increased engine wear and potential engine damage.
Step-by-step explanation:
When oil is too low in viscosity at normal engine operating temperatures, it fails to provide adequate lubrication. Motor oils are designed to maintain a certain viscosity level across diverse temperature ranges to protect engine components. In a scenario where the oil's viscosity is too low, the reduced thickness can lead to increased metal-to-metal contact, resulting in accelerated wear, higher engine temperatures, and potentially causing engine damage. This is because low viscosity oil would be too thin to create an effective lubricating film between moving parts. The Society of Automotive Engineers (SAE) rates motor oils from SAE 5 to SAE 50; the lower the number, the lower the viscosity. Modern engines typically use multigrade oils, such as SAE 20W/50, with additives to maintain viscosity at different temperatures, ensuring that they can function properly in cold starts and at operating temperatures reaching up to 200°C.