Originally posted by bentleywarren:
Four months later:::

I found out that if I disconnect the wiring connector from the water temperature sensor, the cooling fan will run all of the time. I assume that low conductance when the plug is removed activates the fan. Here's my question. If I splice a switch into the wire going to the temperature sensor, could I turn the switch on or off, and make the fan run all of the time? Would I be messing something up electronically? I would only turn the switch off (turn the fan on) when the engine was tending to overheat.






If you disconnect the ECT sensor, it will trip a code in the ECM, and the engine will likely run lean since that sensor feeds temp data to the ECM to help determine correct air/fuel mixture compensation and ignition timing advance. When the engine is really cold, ECM supplies a very rich mixture since fuel doesn't atomize well when cold, and when ECM thinks engine is really warm, it runs a really lean mixture to the engine. You wouldn't want to disconnect that sensor while engine is running. Also because the computer MAY even (on some cars), go into limp home mode, and timing advance will set constant, air/fuel mixture will lock into a preset value, which was a mode designed to 'limp' the car to the dealer or a shop, in case a crutial ECM sensor fails while driving, so you can wherever possible, make it without breaking down.

Best way I think to turn on fans is to just tap into the stock fan relay (on the high-speed trigger), and wire an auxillary switch into the trigger wire, MAKING SURE to wire in the diode to protect the ECM from relay power-down recoil, which can cause a surge and hurt something (relay coils build up a magnetic field like an ignition coil when power is applied, then when field collapses a HV surge back feeds through the circuit). A 0.5 watt diode wired into the trigger wire feeding from the ECM should protect the circuit from this potentially dangerous powerdown spike.

Or you could just wire a completely separate fan relay parelleled directly to the fan itself, so as just to overide the whole fan circuit and make the fans have power whenever you power up the secondary relay (this will not pose any risk to the ECM, but should still have a diode on the primary trigger, since powerdown recoil can still generate sparks that can eventually in time, burn down the contacts inside the toggle switch that you use to turn on the relay.

Also if one was to wire a relay in to turn the fans BACKWARDS in direction, please note, that IF YOU MUST DO THIS, you must ALSO wire in a safety disconnect relay, that will dis-able the stock fan's relay from being able to have the potential to power up the circuit at any time that the fans are engaged backwards! If the ECM were to successfully be able to power up fan circuit while fans were going backwards, this would cause a short circuit and maybe a fire, if proper circuit protection wasn't there. Which COULD burn your car down. So by also wiring in a disable relay for the normal circuit, then you would avoid this from happening. But you would STILL have to remember to turn of the reverse rotation function while driving forward, since the fans would be trying to fight the natural airflow, which could cause an overheat condition at highway speeds and loads, and put unnecessary stress on the fan motor since it would be trying to fight natural airflow. Not good.
By the way, why would anyone deem this mod necessary in the first place?? What is hoped to be achieved? Do you feel your car runs too hot at the track in the staging lanes or something? Because Summit DOES just sell ADJUSTABLE fan turn-on thermostats that can be mounted on the radiator to control the fan. And you can just set it at whatever temp you wanted, and then the fan will continously run until the temp probe you mounted to the radiator is below the set temp setting you put the knob to. Then it would be all automatic. To me, that's the only way to fly. 'Cause when you got some hot chick in the car with you, you wanna be like holding her hand or something, NOT having to play around with a row of toggles and $hit

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