Your not supposed to mix the green and orange.

http://bioengr.ag.utk.edu/Extension/ExtProg/Machinery/Articles/engcool.htm

As this engineer states "The organic acids in orange types will cause precipitation of silicates in the green type"

You need a serious system flush. I would remove the thermostat and garden hose it for a while. If you can get to the heater hoses, I would power flush that also with a garden hose.

Be careful not to spill any antifreeze depending on your local regulations.

If it's really bad, I would have the radiator boilded and flushed at a radiator shop. Whatever it takes to get that crud out. <img src="/forums/images/graemlins/patriot.gif" alt="" />