Originally Posted by BruceK
I`m curious, what do you mean by "vented"? I seem to remember a long while back adding an overflow bottle on a car and having to replace the old conventional "spring" cap with one which sealed the radiator opening.
My mechanic installed Mercruiser recovery bottle systems on my FLs, retaining the standard caps on the tanks, I have wondered how well that works.
Apologies if this overly diverts the thread but I think it relates.
There are two types of expansion or collection bottle systems
#1 One uses a Recovery type cap. It uses two spring loaded valves. One on pressure build up opens directing the excess coolant, from expansion, to a collection bottle or tank. The pressure is contained in the engine to spec.
This cap or the bottle will have a vent hole as it is not intended to maintain pressure, just hold the ejected coolant.
Upon cooldown the other valve opens as the coolant in the engine contracts creating a vacuum which pulls the excess coolant in the bottle back into the engine.
The bottle simply collects the spit out. Simply adding a collection bottle and using the original cap will not work as the old cap will not suck the expelled coolant back. It does not have the two valves. If it does suck back then he installed the recovery type caps.
For this system to work properly the recovery type cap on the exchanger must have good seals and those two valves.. The hose between the expansion tank and the overflow bottle must be fitted tight. An air leak will allow air, not coolant to be pulled back.
#2 Dead cap. The other system actually replaces the function of the engine mounted expansion tank cap , by installing a dead cap, but the overflow bottle now holds the pressure relief cap subjecting the overflow bottle and the hose between also to full pressure all the time. The overflow bottle now is fully part of the pressurized system. Of course the bottle must be more heavily built and must be designed to hold the pressure relief cap or A pressure relief cap.
They both do the same thing, just somewhat differently.
Both these systems will completely purge the engine of air and completely fill the heat exchanger. ALthough the bottles can be used to monitor coolant levels you must watch that the levels rise and fall with heat up and cool down. If not then there is something wrong. coolant loss or an air leak from a loose clamp, bad hose, or failing recovery type cap. I always look for a small leak or it needs a new cap.