Steve, attached is the Hanover cooling system diagram … note all the cooling elements (radiator, hoses, filler bottle) are completely full of glycol (green); only the expansion tank (approx 1 litre, with stant lever cap) has room for air, filled only about 1/3.  The location of the expansion tank is shown higher than everything else in the diagram but can actually be located lower; what is important is the connections be as shown, i.e., highest point of saturated cooling system connects to bottom of expansion tank, expansion tank is only 1/3 full and this is where you install the pressure cap.  Attached is also a photo of my swirl-pot/expansion-tank; note it is not the highest point in the system; the bottom connects to the highest point (water pump outlet); the top is connected to an tire valve for pressurization and also the system pressure gauge. Not shown but later installed, is the rear iron (closest to prop) was T’d into the TOP port of the expansion tank with 1/8” restrictors in hose to remove air from the engine block.

Gurgling sounds are not good; there are two o-rings per iron, per rotor housing. The inner is the combustion o-ring and the outer is the water-jacket o-ring.  If you are getting gurgling sounds then it is possible that coolant is getting past the compression o-ring into the combustion chamber. This can be checked easily but removing your exhaust, turning over the engine by hand and watching for signs of coolant being expelled when the apex seals pass over the exhaust port.  If there is a milky film on the dip stick then it is possible that coolant is also getting past the coolant o-ring at bottom of engine and leaking into the oil sump.  Either situation if true constitutes an engine tear-down and rebuild.  The Bruce-T video is what I used to overhaul my engine/s.

This leads to the question: “Where did your engine come from and what was done to it prior to installation on your project”?

Jeff