I have a 98 Acura CL 2.3 which is overheating at highway speeds. Fans run fine, but they only run if the A/C is turned on. I've replaced the thermostat and coolant. Even with the A/C on (so fans are running) and the heater up at 90 it still overheats.

It's not leaking as far as I can tell, and I've bled it so I don't think its air. My guess is water pump or head gasket, any other ideas?
Yeah the weird thing about the fans is that both turn on with the A/C, but neither kicks on without it on. I'm not sure what to make of that except maybe a wiring issue?

With most Honda products, one fan is reserved for when the A/C compressor kicks on and the other should be controlled by the ECU (depending on the coolant temp) and should kick on and off regardless of the status of the A/C.

You might just have some issue with the non-A/C fan...