Above photo shows the internal parts of check valve inside expansion bottle. The green plastic ball floats in the coolant and is held in place by the black plastic piece vertically fitted inside expansion bottle at top of "elbow".
"Elbow" is seen at bottom left side of expansion bottle. Although being part of the expansion bottle molding, coolant cannot flow from elbow to expansion bottle or vice versa. A small vertical bore containing above mentioned green check valve is the only communication between elbow and expansion bottle.
When filling up a dry cooling system, coolant enters and air is purged out of system as follows:
- Coolant is filled into expansion bottle. Cap must be off and level needs be maintained requiring frequent top up as air is being purged out.
- Coolant flows out of expansion bottle through bottom hose barb marked with a pink arrow in above photo. Coolant flows into return hose from radiator and gradually fills radiator and engine block.
- Air in radiator is purged through green check valve in bottom of expansion bottle.
- Air in engine block and cylinder head must be purged by lifting temperature sensor on thermostat housing.
- Air in heater matrix circuit is purged when lifting temperature sensor on thermostat housing. Coolant enters from thermostat housing and purges air out of heater matrix circuit through return hose connected to top right hand side of expansion bottle.
- Air in rear end of circuit from thermostat housing to expansion bottle is purged through the check valve fitted in disc of thermostat. Of course if thermostat has been modified by removing this check valve, then air here cannot be readily purged out of system. Not really a problem. One can purge by disconnecting outlet hose at thermostat housing or repeat standard bleeding procedure a couple of times after engine has come up to operating temperature. A good alternative is vacuum bleeding.
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