I just installed a rebuilt ballancer pulley in my 56 Oldsmobile. I took the radiator out, and drained it. I filled it back up with water, and let it run. When I took the radiator cap off to the check the water it was foaming a little. Prior to this I had antifreeze and water combination 50/50. There was still some antifreeze in the block. I did not fush the motor. Is this normal? I checked my oil and there is no water in the oil so I dont think its a head gasket. Prior to all of this the car was sitting for a month and a half.

 

What sometimes happens is air pockets are created within the engine block, usually at the top of the waterpump housing, this leads to foaming and eratic temp readings if you have an aftermarket gauge. Here, my water is not really hard, and pretty neutral as far as acidity I just jam my water hose down the radiator neck after the car warms up and force the air out of the system.