Steve Cattaneo

One of my post from 2003



Only phosphate and propylene glycol free antifreeze should be used in any aluminum water-cooled engine. These chemicals are corrosive to any plastic and aluminum in the cooling system. Green and yellow antifreeze also known as conventional antifreeze, contain phosphate, borates and propylene glycol. These chemicals are harmful to aluminum. Green and yellow colored antifreeze were formulated for North American vehicles with cast iron blocks and heads. This antifreeze lacks the needed rust and corrosion inhibitors which aluminum engines need. But most importantly, they don’t contain the buffers needed to keep the PH of the coolant as close to neutral as possible, which prevents corrosion of aluminum.

Do yourself a big favor, on a cold engine, open your coolant cap, if you find green or yellow colored antifreeze (orange colored is ok), drain and flush your system. You must flush to remove any trace of this conventional antifreeze. Fill with approved antifreeze only at a 50/50 mix. Your engine will live long and prosper.

Just because the label says for aluminum engines does not mean it doesn’t contain phosphates, read the ingredients first. It must say phosphate free.

To bleed the cooling system on a 928: Move the temperature control lever, in the center console, to 85 degrees. Run the engine when filling it. Let it reach operating temperature to allow the thermostat to open. Turn the engine off and recheck the cooling level, add if necessary. A completely drained cooling system will take 16 liters to refill. 8 liters water/ 8 liters anti freeze for a 50/50 mix.

Bill Ball

It doesn't matter as long as it is silicate and phophate-free, although the phosphate issue has to do with using hard water causing calcium phosphate deposits. Use distilled water or very soft tap water, and that is not an issue. I use a name-brand, like Prestone Long-life. I still change it every 2 years, although maybe I don't need to. Conventional antifreeze is ethylene glycol, although some are now made with propylene glycol, which is not as good but was substituted because it is less toxic if ingested (which actually is a major medical problem - I used to see a few cases a year when I worked in the hospital - very nasty but fascinating metabolic phenomenon treated by IV infusion of alcohol). There is nothing wrong with ehtylene glycol based antifreeze as long as it is silicate-free.

My 89 was serviced by Porsche and had green coolant when I bought it in 99. When I removed the original water pump at 90K miles, everything was like new inside. I could have left the pump alone. I switched to Dexcool anyway, but soon concluded the Dexcool hype was mostly GM marketing and went back to green or yellow as long as it was silicate-free, like Prestone Long-Life. 100K miles later, no problems.