What is the best closed cooling system out there
 

Any experience from the Coastal Brethren regarding closed cooling systems. I have a lake nearby that has exceptionally hard (alkaline) water. I hear that this is very hard on sensors as well as can cake out at higher temps.

Seoncdly, are EGT's managed by raw water on all inboards? or are there other options out there?

Exhaust is always raw water.