Quote Originally Posted by foama View Post
The coolant flows from the cylinder head where coolant gets hottest, then through the heater core, the throttle flap, and goes to the bottom of the block where it slowly recirculates within the block towards the cylinder head. The thermostat and radiator is being bypassed by this flow, but it is absolutely necessary for the coolant to actually flow within the block especially with a cold engine. Without that flow during warm-up, the cylinder head would overheat while the thermostat which is located in the lower block(!) remains cold.
Btw: The coolant and engine oil have large-surface passages right next to each other inside the lower block which are in effect a very effective oil/water heat exchanger! Thats why the oil temperature at high speed on the highway will not exceed coolant temperature, and also why the oil warms up comparatively fast during warm-up.
The diameter of heater core hoses is much smaller than the radiator hoses. Im confused if the entire volume of fluid goes through the heater core or not? if not, how does the engine regulate water pressure in the heater core lines? im also confused about when the thermostat opens what forces coolant into the radiator if the alternative coolant path thats used when the thermostat is closed has less flow resistance? does the entire volume of coolant go through the radiator? or is the radiator and the bypass(THIS coolant pipe. both operating in parallel?