Abstract: A quick connect diagnostic apparatus for the cooling system of a vehicle engine includes first, second and third temperature sensors which are configured to attach to liquid hoses which circulate cooling liquid throughout the engine, the first sensor attaching to a hose directly from the engine, the second and third sensors attaching to input and output hoses, respectively, connected to the radiator. The sensors are housed within a cuff structure which is wrapped around the hoses to detect the fluid temperatures within the hoses. Each sensor is connected to an analyzer which compares the first signal to a temperature threshold signal, compares the first signal to the second signal to generate a first difference signal which is then compared to a thermostat threshold signal, and compares the second and third signals to produce a second different signal which is compared to a radiator threshold signal.