Every time I install a new radiator, a newly rebuilt engine or tear into the water pump area. I use a small section of hardware cloth= stiff screen with holes big enough to stick the full sized small ink tube of a ball point pen through the holes or slightly larger. It's available at almost any hardware store. Shaped over something the size of a shot glass, so it will fit inside the upper radiator inlet about 2 1/2 inches. Leave enough to fold the extra over the outside of the inlet to secure it in place when the upper hose is put back on to keep the formed screen from making its way into the radiator. A 1/2 inch of folded back screen will be as small and as far back over the outside of the radiator upper inlet as you would want it to go. They sell these screens commercially, but for like $25 or $30 bucks, or make your own for a few cents. Slide the upper radiator hose over the outer screen and tighten up the clamp just beyond the ends of the screen. Start and run your car through several heat cycles. Check the screen right after the first heat cycle to insure you haven't caught so much gunk that the screen is clogging and will block all flow of water into the radiator. You can start the car cold with the radiator cap off and watch * feel the flow of warm/hot water coming past the thermostat. If the flow suddenly diminishes or slows dramatically, the screen could be filling up quickly. Let the car cool, remove the screen, clean it and re-install it, and then increase your cleaning intervals to match the amount of debris it's catching. You might be amazed at what it catches, even out of a seriously cleaned out block that's already been on a dyno. I left mine in for about a week before removing it, as it stopped picking up particles of debris. Once I was done, I had nearly a half a coffee cup full of debris ranging from gooey white aluminum corrosion to chicks of rusty cast iron and gosh knows what else! All this would be in the cooling tubes of my new radiator had I not taken this simple precaution. Best to use reverse osmosis water with high quality coolant. Deionized water has all the minerals taken out of it and it is hungry for some minerals. That's why its such a good final rinse when used in a Hudson Type sprayer after washing your car. It removes almost all the hard water spots before you can dry thee car. I also added the radiator cap mounted (by a small chain) anode from Napa to help neutralize any electrolysis. All my electrolysis stopped after about 3 days with this contraption. I use radiator PH test strips to verify the condition of my coolant these days, especially with the increased use of aluminum parts along with the cast iron. Part of your troubleshooting should be to pull your radiator tip it upside down and back flush it with a garden hose. Use rags and the radiator cap to plug the openings and a rag wrapped around the hose to build up some pressure before you pull the bottom "plugs" out, so you really get some water flushing the crude out of the top of your cooling tubes inside the radiator. Also pull your thermostat when the radiator is out, and using a rag wrapped around the hose, back flush your block and heater core for 10 or 15 minutes. If you have any lower block plugs you can unscrew to assist with the flushing process, remove them too. The comments from the guys above are also great suggestions. Get yourself one of those inexpensive laser heat detector guns at Harbor Freight and use it. Check before and after the thermostat, the engine in various areas and the radiator and hoses. Publish the results on here. There are a lot of smart people on this site, some smart in their heads and some on the other end...lol Learn the heat flow of your engine, so you can tell where and when something is going wrong in the future....once you get this fixed first of course. Good luck.
