Cannondaleriders

You could easy enough add a resistor to your existing sensor to get the cut in where you want it. Let me do a little digging and see what I can come up with. The sensor is an NTC thermistor and I think there's a resistance table in the electrical diag manual. Let me get out the calculator...
The elect diag says the sensor is supposed to cut in at 185????F. Have you seen that to not be the case?

Just looking to simplify here. Swap in a fx400 radiator with switch and your good to go. I already have several methods as a backup .

I'd have to think it may be easier to parallel in a 768 ohm resistor like this one than to swap out a radiator that you don't have. I bet the leads from the resistor could even be fed into the quick connects without having to tap through the wire insulation. A 768 would drop the standard thermistor cut in temp by 30????, which is what it appears you're looking for. If there are different cut in temps for the sensors, then the resistor would need to be different. So, the question there is whether or not the sensor in the radiator is different than the one the put in the engine case. I would think not, but you saying that some don't cut in till 205 is a little puzzling. Are you reading the temp from D&M or some other way? There is always a chance the sensors have drifted. I'd say that every year, I probably toss about 5 per 100 for being out of tolerance. Tolerance is pretty tight though at 1/4????. Occasionally they will just go bad and go way off, too. I spend my days looking at temperatures and thermistors among other things related to making things cold.

Maybe Im missing something here. The coolant temp sensors in the heads of all dales are the same. The mc500 system also uses an on/off temp switch in the radiator just to trip the fan relay. The fan on the 1000 is powered and turned on by the ecm.

I have some new FX400 fan sensor switches.
Maybe you could weld 16mm bungs into the later radiators?

That might work .Shoot me a price.

Dup post

Nope, I was missing something. I didn't know the FX's had a second sensor for the fan. The same thing could still be done, though. Take an ohm reading from that sensor and check the ambient temperature. If you've got 50???? and 3792 ohms (or 41????&4712 ohms or 32????&5896 ohms) or somewhere reasonably in between, they're the same. If you've got something different, it can be figured out easy enough.

The plus to using resistors is that you can change the cut in temp to almost anything you want. And they're cheap! I just saw that the link didn't work, you could google 768XBK-ND and digikey has them for like .08 each. Of course, you can't buy just one but local electronics places carry them.

I think i may be starting to understand what your getting at. But the mc500 which we are converting to has no part in fan control like the 1000ecm. All there is a on/off temp switch in the radiator and a relay for the fan. I dont think resistors are going to work with an on off switch. What your getting at is splicing inline a resitor to the variable resitance sensor in the head to turn on a relay? If you did that on a 1000ecm wouldnt that give the ecm the wrong coolant temp ? Or would you use a separate sensor to turn on the relay. I do know that the `1000ecm has a built in transistor to ground the fan as well as the fuel pump. To bad they didnt build in protection for the system in case of overload. Which is just another reason to ditch the system.

What about adding an in-line fuel pump relay or fan relay. I know I hav seen them in Summit and they are designed to keep and spikes and surges from the fuel pump from damaging the rest of the system. They cost around $30 I believe.