What tool can be used to check the coolant level in a vehicle's cooling system?

The pressure gauge is essential for checking the coolant level in a vehicle's cooling system because it measures the pressure within the system, which indicates whether the coolant is at the appropriate level and if there are any leaks or issues. When the engine is cold, visual inspection of the coolant reservoir can also be used to verify the level, but using a pressure gauge provides additional insights into the system's health and ensures that it operates effectively under various conditions.

Although a dipstick and thermometer serve important roles in other maintenance checks (measuring oil levels and engine temperature, respectively), they do not measure coolant levels specifically. A radiator funnel is primarily used for filling coolant, not for determining its level. Therefore, the correct tool to assess the coolant level within the context of the system's pressure and integrity is indeed the pressure gauge.