Oh no, now you're going to restart the great Water Wetter debate.

I assume you mean 90 C. I wish my 300D would stay at 90C in traffic. I don't believe the thermostat is even fully open until about 95C. I didn't see much result from WW. I found a good flush and refill with 50/50 MB antifreeze was more useful. Let us know if it does anything for you.

Craig