Hi. I've got 30 years of professional automotive repair background and I have never heard of putting a screen in the cooling system to catch "stuff". Not to say that it could not be done, but there shouldn't be any great amount of "stuff" floating around in the system. The best bet would be to flush the system to eliminate any rust and debris. You should be able to find a flush kit at the local parts store. Avoid flushing an old heater core because, many times, this will push it over the edge. If you decide to try the screen program, use a screen with slightly smaller holes than the cores in the radiator. Take off the radiator cap (when the engine is cold!) and look down inside. You will see the cooling passages. The screen needs to be a little smaller than these so that anything that makes it through the screen will make it through the passages. After installing the screen, fill the coolant and drive the vehicle paying close attention to the temp gauge. This will tell you if the screen is causing an obstruction. If it is going to overheat, it will do it relatively slowly so stay close to home. The temp gauge will also tell you when the screen needs cleaned. The running temp will gradually rise as the screen becomes blocked. If your car is not equipped with a gauge, don't try this until you have one. Good luck!