Since I've been using the green antifreeze, I try to do a flush & fill every 3 years.  In October of 2015, I did another citric acid cleaning and noticed that my water pump was leaking at the shaft.  This image shows my water pump housing in my slant six after I ran an 8.1% citric acid solution (1 kg citric acid in 12.3L) for a few days. I drained out part of the solution when I removed the rad in order to replace the pump.  I couldn't finish replacing the water pump right away so the water pump remained half-immersed in the acid solution for a few days.

Water Pump Housing After Citric Acid Flush 15-10-08

 

Because the inside of my engine got rusty during the water pump replacement, I put the citric solution back in and ran it a for a few more days before filling it with fresh coolant.  After less than a month, my new water pump developed a leak at the shaft, so I had to replace it once again.  As you can see, the interior of my engine now looks freshly cast. I'm not impressed with the quality of these imported water pumps but this 2nd pump is still leak-free.

 

Water Pump Housing After Citric Acid Flush 15-11-07

 

I've looked inside the cooling systems of my other newer cars (with aluminum engines) and their interiors look like new. If you keep up with regular flushes (removing old coolant & replace with fresh coolant), the coolant's corrosion inhibitors should keep the engine corrosion-free and reduce the need for chemical cleaning.