The 50/50 mix is the best to stay with. The water in the system is actually the best component for heat transfer.

It is not the mix that prevents the boiling but rather the pressure. When the system is properly sealed the pressure is what prevents the boiling. Water normally boils at 100C (212F) but if you put it in a pressurised container then the boiling point is increased - IE the concept of cooking at higher temperatures with a "pressure cooker"

The fill cap on the expansion tank is what controls the pressure.

Your temperatures are operating in the correct range.

It is true that the 540 operates warm - that is for thermal efficiency which gives you better fuel economy and polution control.

It may also be a factor on the rad and expansion tank problems - the design and plastic may not be up to those temperatures for the long haul. Actually I think another problem is more of a contributor to the failure of the rad necks - that being that the upper rad hose is short, and tugs on the rad neck when you accelerate. If you do repeated rapid acceleration where the engine rocks to the right side then that will break the rad. The right engine mount can also be a factor in this.

For further info about the coolant and mixture see the following

What happens if I use too much antifreeze or water?
Arctic Blend? Universal Antifreeze & Coolant FAQ
Using too much antifreeze or water in your engine coolant can harm your vehicle. Antifreeze concentrations higher than recommended levels can cause problems including corrosion, water pump failure, and increased engine wear. Increasing the concentration of ethylene glycol above 60% actually hurts the engine's freezing and overheating protection.

Cheers
Jim Cash

• 70/30 antifreeze mix better than 50/50? - thisolde39 2008-05-12 17:01:44 (88 views)
  • Re: 70/30 antifreeze mix better than 50/50? - jimcash 2008-05-14 11:15:42 (100 views)
    • Re: 70/30 antifreeze mix better than 50/50? (pic) - thisolde39 2008-05-14 21:49:00 (126 views)
      • Re: 70/30 antifreeze mix better than 50/50? - jimcash 2008-05-18 12:50:07 (54 views)
      • Your pic is quite common for the V-8 4.4L engine. (nt) - hypercritic 2008-05-15 04:50:17 (82 views)