Intermittent overheat.

[jhamelton]

Working on a guy's truck and twice he has left my house, got about 5 miles down the road, and it's overheated. The first time, I did some cosmetic work and replaced the valve covers. Ran it in the garage for about 30 minutes, drove it for about 30 minutes, all good. Guy picks it up, 10 minutes later call me. Truck overheated. Went to his house a couple days later, put in a new 160 thermostat. Filled and drove it for about 30 minutes. All good. Guy called again two days later. You guessed it, overheated again. So it only overheats every now and then. I don't know much about the truck. I believe the motor is stock. I've included the only pic I have of the engine bay. 4 barrel carb, stock intake. Intake, radiator, water pump and raised thermostat housing are all chrome. Don't know if that helps any. It has an electric fan that is hooked up to run all the time. Stock temp gauge. Sensor is in the intake, next to Tstat housing. Gonna get more info from the guy tomorrow. Any help is appreciated.