Folks, I see all over audi pages that they need phosphate free coolant. Is any coolant phosphate free? The jug of Prestone I have doesn't say wether it contains phosphate or not... Does it matter? Will hell break loose if I use standard coolant? I currently drive a 5000S Quattro from '87 and I'm thinking of replacing it with a 90 Quattro from the early 90'ies. Tom