The heater core IS supplied by the port at the right rear of the head on the manifold.
Makes no sense. Is it supplied by the head, or by the manifold? On older engines, the coolant at the back of the head transferred up to the right rear corner of the manifold, and then to the heater core. On TBI engines, that transfer port is blocked except for the "steam hole" as shown in my photo. The bulk of the heater core supply comes from the coolant channel in the manifold, supplied by coolant taken from the front of the head at the thermostat crossover, under the throttle body and fuel/air ports.
So in both cases
the right rear of the manifold supplies the heater core--but the path the coolant takes to get there is entirely different.
What happens to the coolant flow from the left side of the engine?
Virtually all of it travels forward through the head to the front, where it enters the intake manifold at the thermostat crossover. At that point, it could largely stagnate due to a closed thermostat, go out the open thermostat, while a portion of the coolant will enter the under-manifold coolant passage and then supply the heater core.
Coolant flows from the radiator into the lower hose, up into the water pump and is pushed into BOTH sides of the block. It flows from the front of the block around the cylinders on both sides of the block to the rear and it also flows upwards to both the cylinder heads. When it exits the heads it flows into the intake manifold on its way to the thermostat flowing forward.
Essentially correct so far. The coolant flows forward in the cylinder head before entering the manifold at the thermostat crossover.
Part of the coolant also flows in to the port on the intake manifold at the RR of the intake
This is also correct IF you agree that the coolant flowing to the heater core supply at the RR of the intake is coming NOT from the head directly, but from the thermostat area of the intake manifold. The only coolant flowing into the manifold from the head at the rear is what gets past the "steam hole" in the gasket. The heater core supply fitting is getting the huge majority of the coolant from the under-manifold passage that begins at the thermostat crossover.
and flows into the heater core, after it passes through the heater core that portion of the coolant is then returned to the radiator at the port just below the pressure cap. The balance of the coolant flows through the bleed hole in the thermostat until the system reaches operating temp at which time the thermostat opens and allows more coolant to flow into the upper radiator hose and return to the radiator to be cooled by air flow across the cooling tubes.
This is correct IF the thermostat has a "bleed hole". Some--Robertshaw thermostats, for example--are designed with a bleed opening. Others are not. Some folks insist on drilling bigass holes in the thermostat flange for no good reason.
None of this is exceptionally important except that you need TBI intake gaskets if you're using a TBI intake manifold, and the heater core supply fitting ought to be restricted to prevent over-pressurizing the core at high RPM.
This has nothing to do with the restriction in the manifold gasket, The article is referencing using a restrictor in place of a thermostat restricting the entire coolant system.
Correct in that the article references a restrictor vs. a thermostat. The article also mentions that restricting flow to "increase cooling" is a myth.
A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.
The restriction in the manifold gasket is there to SLOW the flow of coolant in the block to allow it to pickup heat,
Not correct. See quote above.
There is still flow from the block up to the heads into the manifold in a TBI engine with the rear port restriction.
There is still flow from the block up to the heads and into the intake manifold AT THE FRONT. There is extremely little flow from the heads to the intake manifold at the rear--only the amount that can "sneak past" the "steam hole".
