I found Motorad uses a time control thermostat If placed into boiling water it takes about 3-5 minutes before it opens fully. If you look the return hose goes uphill. It has a 3/8 inch aluminum pipe plug on the end of the radiator hose at the block. Mine was over tightened I used a 1/2 drive Gedore german allen 8mm socket and it completely rounded out. I had to use a spiral drive easy out. I put a 3/8 brass pipe back in use pipe sealant or teflon tape. You can purchase 3/8 npt aluminum pipe plugs on ebay.
If you can't get the pipe out go to Advance or Auto Zone and get a loaner pressure tester. It allowed me to install about tow quarts. With the plug out I got about 1 cups worth more. I have my own pressure tester. The thermostat end with the spring goes into the block. The cone shaped part goes into the radiator hose. Make sure you bleed to the overflow bottle works watch antifreeze levels.
Does anyone know if brass will react with aluminum and cause corrosion.