350 Heating Up at Stops

[Steeveedee]

At idle, heating is generally caused by lack of air flow. My truck was running hot both at speed (when towing) and at idle. I put a new severe duty fan clutch and 19" 6-blade fan. I removed the stock shroud because the fan was way far into it. I formed an aluminum strap into a circle and made a sheet metal shroud to mount it. After all that, as I was filling the radiator and seeing that the thermostat was opening, I could see that it wasn't flowing much coolant. So I drilled 3 #10 holes in the thermostat, and that brought the water flow up and the temperature down. But the holes allowed flow and it took longer for the engine to warm up, so I bought a high-flow thermostat at NAPA. I have yet to tow the trailer in the highway, but the temps are staying down, now. I put a water pump on it about 5 years ago. It is possible that the thing doesn't pump properly, though the running hot persisted after changing the pump. I changed it because it was leaking.