entrained air

[Norm Keller]

In discussion on another site regarding installing a second radiator, the owner was intending not to use an overflow tank which surprised me. I thought everyone knew about the effects of entrained air but apparently not. Just for reference, the overflow tank is used to accept expanded coolant volume during heating and to return the coolant to the radiator when cooled. Without the overflow tank, the radiator must be run with sufficient air space to provide for expansion. If the radiator is completely filled with coolant, as with race bikes, the coolant will expand, dumping the excess coolant volume. This will be no problem during the race and on cooling the radiator will be refilled. Problems occur if the radiator is not refilled because the air pulled into the radiator during cooling/contraction will mix into the coolant. As a rule of thumb, 2% entrained air by volume will reduce cooling effect by 8%. 4% trapped air by volume reduces cooling by 38%. Thought it might be of interest.