This coolant level sensor monitors the fluid height inside the expansion tank. It sends an electrical signal to the instrument panel when the coolant drops below a set threshold, alerting the operator before the cooling system loses prime. The sensor threads into the tank wall and uses a float or conductive probe to detect the level. A failed sensor may give a false low-level warning or fail to warn of an actual low condition, risking engine overheating. The manufacturer machines the sensing element and seal interface to match the original tank port geometry, so no adapter or thread sealant is required during installation.