I can find thousands of sites on Google that back me up.

Here's one section from a Ford website.

"Even though your coolant in your vehicle is green, it may be sending you the wrong signal. Additives to protect the cooling system may have been depleted and the green color remains. Ethylene Glycol (antifreeze/coolant) will turn acidic when buffering ingredients have been depleted, acidic coolant becomes extremely corrosive and components such as the waterpump, cylinder heads and timing chain covers, can become pitted or worn prematurely and lead to costly repairs. That is why your cooling system needs to be power flushed every 2 years or 30,000 miles."

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".