This may sound a bit strange,but the logic is straight forward.Try adding a cup of Lestoil to the water.We used to add it to cooling systems to help flush them out after a head gasket leak.It is non foaming,does not harm seals or gaskets and will help remove the caked on crud in the water jackets.
I could drain 0.8 gallons each drain. Pretty disappointing for something with about 2 gallons of capacity.
Here's what I ended up doing:
1. Drain and refill with Prestone SuperFlush and distilled water. Run engine 10 min.
2. Drain and refill with distilled water. Run engine 10 min.
3. Drain and refill with distilled water. Run engine 10 min.
4. Drain and refill with about 90% anti-freeze.
5. Drove normal for a week, then drained and refilled with 50% anti-freeze.
I'll wait another week then see what my concentration is, and correct it if necessary.
jon had me take the thermostat out, bolt the housing back in, turn the heat to "really hot" to open it up all the way, pulled the upper hose off the rad, and ran a hose through both ends til the water came out clear, after the initial drain... worked nice, and then drained the system once again to mix the coolant...