auto air vent

ok, just wondering...have you guys ever heard of anyone putting an air vent on the high side of thier coolant system to eliminate bubbles in the system? I'm a plumber / pipefitter and when we install heating or cooling systems we always put air vents at the highest point in the system. In fact, we use an auto air vent...it's got a bladder in it that allows air out while the system is under pressure. Anyone ever heard of using something like that on our closed loop systems?

The cap on the closed coolant system works like that, if I'm understanding you right. At 14psi. it starts to vent to maintain a constant pressure and keep the boiling point higher, then as it cools off it allows some air back in when the pressure drops.

Bored400 said:

ok, just wondering...have you guys ever heard of anyone putting an air vent on the high side of thier coolant system to eliminate bubbles in the system? I'm a plumber / pipefitter and when we install heating or cooling systems we always put air vents at the highest point in the system. In fact, we use an auto air vent...it's got a bladder in it that allows air out while the system is under pressure. Anyone ever heard of using something like that on our closed loop systems?

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I'd also thought of an autobleeder but decided the glycol would likely screw it up. Somebody recently mentioned cutting in a "T" on the top radiator hose with a screw cap, to bleed. I imagine something similar could be done with a bleedercock.
Most of the air that gets trapped and causes problems is upstream of the thermostat. The rest usually finds it's way out of the system eventually.
Buying a thermostat with bleed holes or drilling your own in the thermostat also seems to help.