[Lucky Dog 33]

I’d def start with the HEX. Without proper cleaning and inspecting, they will fail prematurely. Take it off and pressure test it. Do you know if they are original?

If it turns out to be the hex, make sure you flush the entire system before filling up with fresh coolant. As previously mentioned raw water can get sucked back into the system at cool down and you will have a mixture of old coolant and raw water, which will just cause future heating and/or corrosion issues.