[cycleguy55]

Originally Posted by patrickt

OK, without seeing a schematic of your setup I'm just shooting from the hip to a certain extent, but "yes" they do fail, and DC motor speed controllers that are PWM can fail more flakily, if that's a word, than say just a plain old big ass resistor. The latter just tends to burn up and not work at all while a PWM is just a big switch that turns on and off really fast. There's also circuitry involved that senses how hard the fans are pushing/drawing because moving hot air when your engine is running hard is completely different from when you just throw your switch on in the garage and proclaim "yep, the fans are working fine." Remember, you only have a couple of components in this little circuit: the fans, the controller, the temperature switch in your radiator hose, the relays and the override switch. Plus the connections everywhere and your little light. I don't think it's the little light. Dual fans can draw a good 30 amps and dual relays are good, and connections are important. If I were diagnosing this in the garage I would do a voltage drop test along the circuit to see if there was any unusual resistance and then I would immediately suspect the controller. I would bypass the controller so the fans were controlled by the temperature switch in the radiator hose and the manual switch exclusively -- and they only have one setting when running, "full blast." Then I would drive it a few times and if everything was fine I would just replace the controller. But if the temperature switch in the radiator hose won't trigger properly then check that it has a good ground and good connection to the relays and just replace it. You can always test it with a VOM and a pot of water on the stove if you are so inclined. But your problem is going to be one of those components. I promise.

While I've thought of going to a switch / sensor in the lower radiator hose (or tank), my controller has an attached probe that goes in the radiator fins, so I can't bypass the controller and use just the "temperature switch in the radiator hose". I'll take your suggestion to test it in a pot of water using a VOM, though.

Thanks.