I have an odd thing happening with my YM 336 Cooling System. Had a blown out lower hose and replaced it, but noticed no water flow out of my upper radiator hose into my radiator and concluded that I needed to replace the water pump. Did that and still no flow! (I am in FL and run without a thermostat so I knew that that was not the issue). Radiator is not clogged. I took off the lower radiator hose and the upper hose and back flowed water through the engine and out the lower hose. Reconnected everything and had water flow while running. Thought I had fixed, however let engine cool and started it a few hours later and again, no flow. I repeated the back flow and achieved flow again while running, but after waiting some hours and restarting, it returns to no flow!!!??? I have back flowed several time, but keep getting the same result. Any ideas on this?