Reply to "cooling system advice ??..."

Larry, you wrote your post after I had already begun mine.

Lift the hood on any modern car and you will find an air bleed system just as it is plumbed here, this is nothing new. Open up Carrol Smith's books "Prepare To Win" chapter 8 or "Engineer To Win" chapter 10 and you'll find a race car cooling system with swirl tank, fully described.

The air bleed hoses are small diameter, 1/4" ID is plenty big, so the amount of hot coolant recirculated from the swirl tank to the "surge tank" (formerly the overflow tank) is minimal. I've specified pulling the air from the radiator's outlet tank, so that coolant has already been cooled.

The cooling system has three pressure zones: the highest pressure is the pressure in the block, the intermediate pressure is the pressure between the thermostat and the radiator, and the lowest pressure is the pressure between the radiator outlet and the coolant pump inlet. The swirl tank is in the intermediate zone, the surge tank is in the low pressure zone, so coolant will readily flow from the swirl tank into the surge tank. The radiator outlet tank is in the same zone as the surge tank, it doesn't seem to me that coolant would readily flow towards the surge tank from the radiator outlet. But I've checked under the hood of several cars and have found them all plumbed this same way. Carrol Smith also specifies the radiator air bleed plumbed this way. I can only guess that since air rises, that as long as the surge tank is higher than the radiator the air will migrate towards the surge tank.