Jeff mentions “OATs” so I thought I would elaborate

(The bolding and underlining are mine and may relate to the sludge some of us have found in our heat exchangers.)

“Automotive antifreeze/coolant is made of ethylene glycol, water, and a chemical additive package. For many years, there was only one type of antifreeze on the market, conventional green. Antifreeze technology has become significantly more complex in the last several years with the introduction of Dexcool and other extended life antifreeze formulas. Currently, there are three main types of antifreeze on the market. They all contain an ethylene glycol base, water, dye and an additive package. What makes them different is the additive package.

Conventional green antifreeze formulations usually contain a number of inorganic corrosion inhibitors that provide immediate corrosion protection because they maintain the pH of the solution (buffer it), but are consumed or transformed chemically as they perform their