TurboTime

As mentioned, I think if your coolant is murkey, it has a stop leak in can added. Flush with water and refilll with the non phosphate solution - don't use DEX-COOL by GM. Drive the car, if it gets hot, look at replacing the radiator. Our rads are all getting up in years. Money well spent to prevent premature head gasket problems. I had a single fan go out on a PCA climp up Mt. Whitney, and overheated. I was soon replacing the headgasket.
Some of that was from 20psi too. Now, I'm down to 18psi.

Make sure you burp her good. I got a Mitey-Vac system for ~$60, and use it on all my cars. Vacumms the air out (using your air compressor) and sucks new coolant in its place. Love this tool!

DDP

If you are going to flush out the coolant with water, use distilled water. If you use regular water, which has minerals in it, you could leave mineral deposits. Distilled water doesnt have any minerals in it. Good luck.

84black944

When i did the radiator in my 84 i was going to flush the system but my dad said that flush is for getting rid of rust and stuff you dont get in all alluminum engines. Watch out for the radiator drain when i removed it it shot out like a hose on full, and the block drain makes a big mess all over the header

KuHL 951

The best reason to use distilled water with a flush is it will actually help remove mineral deposits. Being mineral deficient it will disolve deposits as it tries to reach equilibrium with it's environment. Never think that distilled water is non-corrosive; it's in an unnatural state and will quickly remove passivation on aluminum if not used with inhibitors.