What tool is used to check the fluid levels in a car?

The use of a dipstick to check fluid levels in a car is essential because it allows drivers and mechanics to accurately assess the engine oil level and, in some cases, other fluids such as transmission fluid. The dipstick is a long, thin tool that is inserted into the vehicle's engine oil reservoir. By pulling it out and observing the markings on the stick, you can determine whether the oil level is within the recommended range. This is crucial for maintaining engine health, as insufficient oil can lead to serious damage and decreased performance. The design of the dipstick is specifically intended for this purpose, making it the most reliable tool for checking fluid levels among the options.

Other tools like a wrench are used primarily for fastening and loosening parts, while a thermometer measures temperature, and a gauge typically indicates pressure, temperature, or another measurement, but they do not provide the specific information about fluid levels that a dipstick does.