I bought a 93 ES300 with 100K miles. It drives and looks like brand new.

Problem: I found that the cooling system is contaminated with rust.

I had the system flushed. My mechanic says that the rust problem will continue because there is no long term solution to rust contamination in the cooling system.

After the flush I drove my car home and when I shut the engine off coolant started spilling out of the overflow reservoir. The it stop doing it for a few days and then it did it again.

Temp gauge shows normal temp, but coolant inside the reservoir looks hot and bubbles come out the hose that enters the overflow reservoir.

What's Up?
Did I buy a problem with no solution?
Is there a relation to the rust and the overflow of coolant?
Can anyone help?