My 940T uses a green cap, as does my 940 NA.
A coolant pressure test on the 940T showed up a knackered heater tap, which was leaking coolant.
The cactus heater tap was replaced with a Gates tap for a VT Commodore, which has 4 ports. Under vacuum in this configuration, the tap both isolates the heater core, as well as providing a coolant return to the head. The standard configuration just stops coolant flow to the heater core under vacuum and doesn't provide any flow back to the head.
The standard config is a nice way to cook and melt your engine on a very hot day when you engage Recirculation, because this is when vacuum is applied to the heater tap.
