I got into a little front end collision last year and it slightly bowed the radiator. That's the first thing. It has been running fine since then. So the a couple weeks ago I looked at my gauge and it was running hot. I parked it and the radiator reservoir was empty. I pulled the bottom hose and pumped some water in it and the fluid was real rusty looking. I then connected it back and filled it with radiator fluid. It was running fine. Today the truck started to run hot so I checked it and the reservoir was empty and just filled it with water as I was stuck on the side of the road. As I drove home it kept going up and down as my heater kicked on and off. If the heater was blowing it was at normal temps but once the heater kicked off it went back up. It never fully overheated but got to about 90% a couple times. Any suggestions? Water pump seems fine.

 

Find the leak, obviously.