What you are missing is the fact that water is not circulating up under the thermostat. The t-stat is mounted in a housing that is up and away from the block like all of them are. The only heat getting to it is from heat soak. The water is not moving across the thermostat, it has no where to go. The small air bleed hole that is standard on most thermostats is not enough, the water in the block simply heats up to fast. By adding a heater core to the system or more air bleeds, the water can now flow across the bottom of the thermostat heating it and the block evenly. Lots of engines do the same thing, most just don't notice it or think anything of it.
All heater systems are plumbed with hot water out of the top, through the heater core, then back to the water pump, its a constant circulation. In this case, the water exits the t-stat housing so water has to flow right across the bottom of the thermostat on its way to the core.
The fact that this engine goes to 220 only means it is heating up fairly quickly, possibly from running lean, fuel quality, tight tolerances, or poor casting of the block or head, doesn't mean there is something wrong. Since the modification, it's now working correctly.
I see this with my 250. The heater hose has a positive shut off inline, so my temp gauge also climbs higher the t-stat then settles once open. With the valve open the gauge shows an even heating with no spike.
Thermostats need to see hot water on the bottom side only. Inside the spring loaded brass piece is special wax that when heated pushes the valve open. The spring is only there to close it back up. You can have ice water on top and still not effect the way it works, but you must have heat on the bottom. With out circulation, the water simply heats up faster deep in the block then it does up in the t-stat housing. The water pump cannot move water if it has no where to go. The only exit out of a engine with no heater system is through the thermostat or the very small air bleed in the thermostat. There are no internal circulation holes or ports, so water just sits till has a place to go.
If there was a problem with the cooling system, the temp would not settle back to the set level and stay.
Joe
Last edited by Joe H; 03/01/2015 4:04 PM.
