Does your rad \"sip\" from your overflow tank? This may be dumb, but I've never really thought about it before? When your rad gets overpressurized it will burp air(and coolant) out through the rad cap and into the overflow tank. I know that......../forums/images/icons/tongue.gif BUT...... If your rad is a little low, does the overflow tank act as a reserve? Does the rad cap act as a vacuum and pull coolant back into the rad? If it does, can somebody explain the physics of it to me?