F350 6.0 power stroke
 

I'm having overheating issues. Replaced the thermostat and radiator overflow cap but it's still getting hot enough to leak out of the cap. But not registering on gauge as overheating. Any ideas as to what is going on?

Welcome to the site..

Couple things that happen are,, if the headgasket/s leak, it lets compression pressures into the cooling system, raising coolant temps, and over pressurizing the system and expelling coolant from the degas bottle.. If the engines oil cooler restricts, it then reduces coolant flow to the EGR cooler next in line, raising compression/combustion temperature and pressures which helps in failing the head gaskets.

What year 6.0, and miles on the clock?

It's an 05 with 240k miles on it