With out circulation at the thermostat, the water in the block is going to heat up faster then the water in the thermostat housing. It is going to take some time to transfer heat to the thermostat (remember, no circulation), so while that is going on, the block is going above the thermostat setting. Once the thermostat has enough heat to open, the rush of hot water will cause the radiator to spill out due to high heat and pressure. After a brief time the system averages out and works as normal.
No blockage, or broken parts, just a incomplete system.
If the heater hoses were attached, or the heater core bypassed with a loop hose, this would not be a issue. Water would circulate around and under the thermostat creating a smooth even heating.
The owner created his own bypass with three small holes. Its working, he's happy, and the truck is happy. The only down side to drilling a lot of holes is you can slow down the heating up of the engine.
What's so hard to understand?
Joe
