RE:'95 A6 Quattro, 2.8 with 197,000 miles. I see a reddish/brownish deposit on inside walls of plastic expansion tank. Also fluid seems to have a brownish sediment mixed with liquid. Getting heat but not as hot as originally.

I want to flush system and install new red Pentosin coolant. I have an air compressor. Is flushing just a matter of opening the drain at bottom of radiator, running water hose into expansion tank till drain water appears clearwhile engine is running and then applying air pressure at opening of expansion tank to force out all fluid?

Any tips on this are appreciated. Thanks.