The aux. electric fans engage at high speed at 105C (about 221F) coolant temp. and disengage at 100C. In addition they are activated at low speed by the AC system high pressure switch if not already running at high speed based on coolant temp. On some modern cars the fans don't engage until about 230F. Most manufacturers have eliminated gages and replaced them with idiot lights because customers complain that the car is "overheating" at 200-210F.

IMO the OE cooling system is very effective, and I think you're better off fixing any problems with it rather than cooking up a home brew solution. Temperatures up to about 110C (about 230F) are normal for extremely hot weather in stop-and-go traffic.

Maximum antifreeze concentration should not exceed 70 percent and 50 percent provides freeze protection down to about -35 F and boilover protection to about 265F (about 130C) with a 15 psi cap while having more than adequate corrosion protection additive concentration.

Water has greater heat capacity than glycol, which is why running over 70 percent glycol is not recommended.

What's the highest temperature reading you're seeing on the dash gage?

Duke