Replaced Coolant and Rust everywhere

I used flush and everything.

I had to remove one of the hose to the heater core and run water through the whole system in order to get all the lose rust out.

I flushed my coolant system 5 times and finally got all the lose rust out but all the surfaces have rust on them but will not come off.

Why would there be so much rust in a coolant system for a truck that is a 2000 C3500 with 5.7 with 100,000 miles.

Did it sit for a long time?

I know someone replaced the coolant once since the plug is broken off.
I had to remove the bottom rad hose to drain the system.

What kind of coolant came out when you drained, what color besides rust? This troubles me i have a same year truck...JJ

There was a little green and a little red but about 1%.

I am hold coolant and the engine is running really cool.

I do have a 160 them on also from Jet Chip. I found out that the guy before me had the complete package put on my jet.

well maybe there was to little coolant period. This will cause major rust probs. You might go ahead and put correct factory recommended coolent back in as some say it best handles the iron block and aluminum head combination of metals. I would take it to a garage or jiffy lube that can perform the power flush precedure they have now, then put put the required 50/50 ratio back in...JJ