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Fuel pump relay getting warm normal?

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Car is a 95 Toyota supra and I just installed a walbro 450 high pressure fuel pump. Knowing that it can draw more amps compared to a walbro 255, I opted to install a Bosch 75 amp relay. (I originally ordered a 50 amp but the supplier was out of stock and sent me a 75, which I know is overkill.) Battery is still in the engine bay, so I figured running 8 gauge wire from the battery to the relay would be ideal. Upon the car driving for 30 minutes or so, the relay is warm to the touch but none of the wires on the relay are. I know relays will get warm but I am curious as to what would classify it as being to hot? Is it a problem if only the wires are getting hot?

According to this Bosch Relay Data Sheet, all of the Bosch relays are good for 65-100 degC (149-212 degF) ambient conditions. So if you can still touch it with your hand and hold it there for 10 seconds, it's less than 65 degC and I wouldn't worry about it.

I would measure the voltage drop across the relay to determine how much internal resistance it had if I was really concerned.

Awesome information. Thank you David!