Originally Posted by Infinite Monkeys
Thanks for that extremely informative reply. You saved me from making a big mistake. Since I am not going to put in a heater for now, I was going to block off the manifold port and just run the upper and lower radiator hoses. I did not realize that the coolant needed to circulate before the thermostat opens.
Another question is: what direction does the coolant flow when the thermostat opens. Does it go into the engine from the top of the radiator, or out.
It comes from the bottom to the pump typically into the block, up to the heads with return collected at the front using the intake manifold as a location to put the passages. The manifold houses the thermostat and return fitting which then sends the return coolant to the upper radiator connection.
While this description covers a great many engines including the SBC not all are configured like this. The early Chrysler Hemi's followed this basic scheme but the return was separate from the intake manifold and external using a fitting on the passenger side and a hose to connect to a bolt on thermostat housing on the drivers side with the radiator return from there. The 1990's LT1 and LT4 with reversed cooling puts the coolant into the head first then to the block and uses a complicated mixing system that adds just enough cold coolant to the hot to maintain a very tight operating temp. The new LS engines also use this system. At GM reverse cooling came out on the Pontiac engine in 1955 and was used through 1959 production. The system proved to be troublesome in service this being a period of transition trying to get the motoring public to adapt the use of glycol coolants instead of straight water, or water mixed with a dissolveable oil (water pump lubricant). the other problem was steam formation in the heads above the rear combustion chambers which was not solved till the LT1/4 with nothing more than a small bleed tube from the rear to front of the heads then connected to the pump's suction side. There are, also, many other coolant routing schemes both by the factories and by the racing community.