overheating 318

I can tell you what I've found... I must say that the only reason for my removing the freeze plugs is 1 behind the starter stayed damp from just the tiniest seepage. The one was rusted almost completely through. Anyway.. Once it was removed I discovered huge chunks of rusty crud and previous owners stop leak. So much that the next freeze plug forward was knocked out and the same 2 on the other side. High pressure hose under the car. 1 hour job turned into day and a half. Total of 4 freeze plugs replaced.
Here's what I think I learned... Any and all material in the water is going to settle at the lowest and farthest location from whatever agitates it ( shaken or stirred ).
Not only was the stuff restricting flow but some heat soaking was occurring too.
Flow through a radiator, a system that holds water and water pressure, all important.
Circulation throughout the system is also important.
Adding a coolant recovery setup will keep air out of the system to help prevent rust.
Honestly... I like raising the hood and seeing clean green fluid at the correct level in the bottle. That tells me nearly everything I need to know about cooling system health at a glance.