Hi Steve, along with having a hole in the thermostat you should also have an air bleed at the highest point in the water system.  I have 2 - one is attached to a hose connector in the rear housing just behind the re-drive - the other is at the top of my water pump outlet; both use 3/8 hose with plugs drilled to 1/8 inch and they tee at the bottom of my small expansion tank.
Jeff - Wishing all the best in 2018.
Sent from my BlackBerry® phone powered by Koodo Mobile®.