Problem just started. I did have a radiator leak in lower corner. Had a radiator put in about 7 years ago. The shop must have lost the lower rubber mount where it leaked because it was missing when I pulled out the old radiator.. Guessing it bounced around and finally a bad leak.
Replaced the radiator. Replaced the hoses, some heater hoses . Did just fine. Then started to overheat a couple days later. The electric fan wasn't turning on when near overheating. I have a manual switch in the hood to turn it on during smog time. I pulled out the electric fan. Fan turned on fine. Reinstalled and it was working. I was thinking when I put it back in from the radiator replacement, I tweaked it. Hooked the regular connection. And it was fine. Until yesterday. Wasn't turning on. Turned on the switch and fan working.
So I'm thinking something controlling the fan isn't working. Or the fan is an intermittent problem. What controls the electric fan? Is it a temperature sensor. then to a relay?
What should I check and how?

 

The sensor/sending unit that controls the efan is in the t-stat cover.

 

How do I check that sensor?
Boiling water with volt meter attached and check for output? Or just replace it? They are not expensive. Don't think its the same sensor registering with the Temp gauge on the dash? .