The way I tested mine was from inside the dog house I stared at the top and went across the top every several ins. I had to hold the fan clutch with a rag and re position it to take the readings. Working my way across and down in about a 2 in grid pattern I took readings until I got to the bottom. What I found was a 52 degree difference from the inlet on top to the outlet on the bottom and no cold spots especially in the center of the radiator. I am told the the center,area where the electric fan covers is the likely area for clogging. I have had several brand new thermostats that would not open or only partially open right out of the box. Always test in boiling water first. I change anti freeze and chemically flush first then flush by removing the thermostat, replacing the housing and forcing water into the system through the lower radiator hose. I made an adapter to do this. If you put a pail underneath you can see what comes out of the radiator. Also when you remove the cap the water should flow freely out the bottom inlet, if it kind of gurgles out it would indicate some restrictions. Hope this helps you out.
