Still no diff
 

I was not suggesting to use water alone. My point was that the charts show that adding WW (or PI I guess) has little additional cooling effect, and therefore is an unnecessary additional expense. There may be other benefits not shown on the charts and since I have not used the stuff I cannot comment on that. Other that optimizing the mixture ratio as you suggest, the only thing I think would be useful is to keep the radiator passages free and clean.

Best regards,

JL

For what it's worth I tried WW once in my 300D which was running a little hot with old (green) antifreeze. I did not notice any difference in operating temperature. After flushing the system acouple of times and putting in a 50/50 mix of MB antifreeze the temperatures went down. I have not tried adding WW to the correct antifreeze mixture, and don't plan to.