Block rust, coolant change over due

[brods]

Changed the water pump today and here is what the block looked like:

I thought I'd changed the coolant in the last couple of years, but it must have been on another vehicle. Looks like I did it last in Nov of 2010 at 93K miles. 141K miles now and coolant 7 years old. So besides the normal distilled water flush, anything else to do about the rust or just add new coolant?

 

[Motorhead]

I have used citric acid granules. Mercedes Benz recommended this when I had a 5 cylinder diesel. It was safe in all cast iron engines or mixed metal engines. The ratio is about 1 pound to 2.4 gallons of water.
Here is a link to a MBZ site. Read post 2 as that is the instructions from the MBZ manual. http://www.benzworld.org/forums/w12...3937-mb-citric-acid-cooling-system-flush.html
I have personally used this "recipe" to clean several cooling systems. It does a good job and doesn't take out the water pump seal.
Citric acid granules are readily available. Amazon: https://www.amazon.com/Citric-Grade-Granular-Organic-Anhydrous/dp/B0149E1IH6

 

[brods]

Thanks, that is interesting stuff. I was hoping that those guy's who see these engines all the time would say if the rust is normal and not to do anything about it or if it worthy of cleaning.