beltfed,
A "smartie" huh!. I am only going by the little picture I linked...having never dinked with one of these. The valve in question isn't a simple ON/OFF valve (I think). There is a small bulb/capillary tube affair that sits in the cab and signals the thermostatic valve to open or close to some degree...a crude climate control.
This valve needs to be on the downstream side of the heater core so the core is always charged with 'hot water'. The valve is adjusting this gradually...allowing more through to bring the heat up and closing to cool things down.
This is how I assume it works, but I have been know to be wandering in the fog before.
Stuart
