Coolant bleeder valve purpose and operation
 

I'm leaking coolant out of my bleeder valve, so I've ordered a replacement. While I'm waiting for it to arrive, I've been trying to understand exactly what it's doing.


1. When the coolant warms, it expands and builds pressure. Is the tank at the same pressure as the rest of the system? Or is it at a lower pressure? Will coolant spray out if I open it while hot?

2. At 13PSI, the valve opens to release pressure. What's being released? Just water vapor? Are the additives vaporized as well? No liquid will be vented, right?

3. If water vapor is released every time the engine gets warm, why doesn't the system need regular refilling?

4. As the engine cools, the pressure will drop. At what point is air let back in through the bleeder? At atmospheric pressure? Negative pressure?

5. Why would I ever want to put the clip in the up position to force the bleeder open? Can't it bleed normally as the engine warms? I've read that people run with the clip up on the track; why?

Thanks! :)

I'm probably opening a can of worms by attempting to answer this but...

Yes same pressure, yes of course if under pressure it will have to go somewhere.


I dunno if it is 13 psi but air is lighter than water so what gets release is on top. Some coolant will be forced out in the process

Ideally only air is purged, once that is gone, it grabs what coolant it needs from the coolant over flow/expansion tank.

It should not allow air in the bleeder, coolant is drawn thru the expansion tank as needed.

When you drain or service the system there will be large amounts of air pockets in the system, This trapped air is not easily removed without forcing the bleeder open.