Niall,
I currently ahve an Edelbrock manifold.
According to RPi's site, and I quote : "Rover intakes have always and necessarily had this type of coolant bypass allowing for a slight volume of coolant to continuously circulate even when the thermostat is shut. without this required feature, incomplete Weber installations kits will lead to problems with coolant circulation and higher engine running temperatures,"
There's still one other solution, I guess : there's an other type of hose that can be used ( instead of opening the extra outlet on the back of my water pump); this hose has 4 outlets ;
1. connection to the water pump
2. connection to the radiator
3. connection to expansion tank (return )
4. connection to heather ( as return)
This way I can use the one outlet of the waterpump to connect to my intake manifold , from the back of the manifold a hose will feed the heater, the return will then be connected to the big return from radiator to water pump....Will this do also ?