So, you used a jumper wire to only eliminate the temperature sensor and this leaves the fan on all the time?
I'm not familiar with the specifics of the temperature sensor and fan system, but if you're sure that's the only component you jumped, that doesn't make sense to me that it wouldn't work.
A very simple way of describing it's operation would be (where all components are in series):
12V Source ---- Radiator Fan ---- Coolant Temp Switch ---- Ground.
Basically, the radiator fan doesn't kick on until the Coolant Temp Switch reaches a certain temperature (227 F) which acts as a switch, closing the circuit and allowing the fan to run. When the Coolant Temp Switch is cooled off to a certain temp (220F I believe) the switch opens back up, cutting the fan off. Cycle is repeated as necessary.
Grab your multi-meter and check continuity of the wires going to the temp switch. One should read <1 ohm to ground, the other shouldn't read anything since it comes from the fan. The only thing the switch does is close the fan circuit to ground.
If the switch is operating correctly, I would say either the terminals to the switch or the wires are not connected properly.
I was thinking the same thing. But the fact that I can jumper the CTS connector plug out, essentially acting as though the CTS reads a temp of >227F makes me believe the problem is downstream of the connector. What do you think?
I think Pistol
may be right about the radiator needing flushed. Since I've already verified both sensors to be working within the same range, that seems like the most likely problem. I just have a hard time believing the radiator temp doesn't soak the sensor even with a low flow condition.