In most cases, this indicates a problem within the circuitry of the fuel system, as a fuel pump relay can become hot from electrical resistance, overload, etc. The relay acts like a switch that controls the 12-volt power to a fuel pump where it can run at the right pressure, usually between 40-60 PSI for most vehicles. If the resistance is high—and that’s often due to corroded or loose terminals—the relay generates heat because electricity is having difficulty flowing through the circuit. I have seen studies showing that sometimes this added resistance can raise the relay temperatures by 20-30 degrees Fahrenheit (or more), significantly shortening its service life and damaging nearby components.
A circuit overload is another very common cause of a fuel pump relay overheating. Fuel pumps require a fairly stable current, especially in high-performance models over 100 PSI. During high demand periods where connections or fuses are not properly rated, the relay has to pass extra current to meet demand, generating heat. In an automotive electrical study, it was found that relays overloaded by 50% lose up to 15% of efficiency and tend to fail subsequently when subjected to high demand indicating component rating may be the most important design consideration.
If the relay isn’t designed for a continuous load, it can also heat up due to a running fuel pump. Generally speaking, if the engine does not require the fuel load, the relay will switch off. But if a relay gets stuck in the on position it will then keep throwing current at the pump which will simply increase heat and wear. If the relay is found to be very hot, mechanics advise checking for continuous operation and see if it is a case of a stuck relay or a wiring problem in the pump’s control system.
For instance, conducting preventive maintenance and checking the fuel pump relay and wired connections to the pumps can help spot any problems in its early stage and facilitate the safe and efficiency operation of the pumps. A worn out or overheated Fuel Pump relay can cause a circuit overload which can lead to overheating of the circuit and is a potential risk on the long term reliability and function of the pump so replacing it is the solution.