best way to purge air from cooling system??

[70 RAG TOP]

How important is it to get air out of cooling system?  I am about to start my newly rebuilt engine and have read that you need to purge air out of your cooling system to avoid hot spots that can damage the engine.  If it is important, what is the best/proper process to purge theair out?

Thanks

Mike

[Chryco Psycho]

the only trap is the thermostat , I usually drill a small hole in it to allow air out , it would take a minute or two to pull the housing & either drill a hole or let the air out & reseal it . Or you could pull the heater hoses off & let the air out that way

[70 RAG TOP]

how big of a hole? and on what part of the stat should the hole be drilled?  I assume that it would be somewhere on the flat part of the flange.

[Strawdawg]

1/8" usually is a good number

[femtnmax]

   with all the above.   Many of the new cars have small holes with/without check valves that let the air bypass the closed thermostat.
I add the 3/32-1/8 hole to all my thermostats that don't already have one.  This eliminates nearly all the air from the system.  Just fill the cooling system somewhat slowly...not just dump in real fast...you will hear the air gurling out as you fill it.

[GoodysGotaCuda]

I have a fancy vacuum fill system I use, but that was more for problematic BMWs that would catch air pockets. Without it I usually run the heater wide open and allow flow through it. Let it get warm, while still warm I pull the cap (as long as its safe to do so). Do that 2 times or so, top it off, and it's good to go.

[brads70]

  with all the above.   Many of the new cars have small holes with/without check valves that let the air bypass the closed thermostat.
I add the 3/32-1/8 hole to all my thermostats that don't already have one.  This eliminates nearly all the air from the system.  Just fill the cooling system somewhat slowly...not just dump in real fast...you will hear the air gurling out as you fill it.

I do the same.

[daveh]

Another trick is to lift the front of the car as high as you can while running it and filling it with the cap off.  That will clear the lines.  I use car ramps and it has never failed me.  Good luck