What is the criteria for checking engine oil within the engine compartment?

Checking engine oil is a crucial part of maintaining a vehicle, and the correct criteria involves assessing both the cleanliness of the oil and ensuring it is at the proper level. The oil should be clean, indicating that it is still effective in lubricating the engine parts and has not become contaminated with dirt, debris, or combustion by-products. Additionally, the oil level should be at the full mark as indicated on the dipstick, which ensures that there's enough oil present to provide adequate lubrication and prevent engine damage.

Thus, having oil that is clean and within the full mark demonstrates that the oil is both in good condition and at an appropriate volume for proper engine function. This ensures the engine operates smoothly and efficiently, reducing the risk of poor performance or mechanical failure.

The other options do not provide relevant criteria for checking engine oil quality or level, as having a strong odor, a specific color, or a certain viscosity can be subjective and may not accurately reflect the condition of the oil.