Quote Originally Posted by Dougal View Post
While we're on this topic. Does anyone know if the soft-dash heater runs a tap or valve on the hose on the engine side of the firewall?

Mine has one. I don't yet know if it is a dodgy replacement for a factory item or a dodgy addition.
The lines are still connected which suggests the heater core isn't leaking.
I've spotted a heater valve on most of the soft dash models I've come across. It's a 4 port bypass valve operated by a vacuum solenoid on the firewall. The valve is similar to ones used on Commodore V6s (16mm fittings) and some Falcon V8s (19mm fittings) of the later 90's.

Here is one installed on a P76 to cut heater flow without stopping coolant flow through the rest of the heater circuit.