The radiator is about a year old - the last one broke off where the top hose connects (fortunately close to home) and I had to replace it.

I pulled the high temp sensor (from reading other posts, it was supposed to cause the auxiliary fan to operate on high speed) but it didn't move...

Can you pull the power source and connect it to a 12v battery to see if it will run on its own?

Thanks for the response.