A couple of things. First of all, since the thread is nearly 7 years old so I truly hope any problems that were presented in it have been solved. Second of all 50/50 antifreeze-water mix gives the best cooling in my experience. Having tried most all of the other additives available over the years, it always comes back to water and antifreeze doing the best job under normal conditions. The key being what you said. ("If your cars cooling is in good shape"). I've run extensive tests with straight water also and you'd be surprised how quickly rust begins to form in an engine. So, straight water is something not even worth considering. Who did you 'hear' this from?

http://www.engineeringtoolbox.com/ethylene-glycol-d_146.html

Note! The specific heat capacity of ethylene glycol based water solutions are less than the specific heat capacity of clean water. For a heat transfer system with ethylene glycol the circulated volume must be increased compared to a system with clean water.

In a 50% solution with operational temperatures above 36 oF the specific heat capacity is decreased with approximately 20%. The reduced heat capacity must be compensated by circulating more fluid.

In racing most places won't let you run antifreeze, because if you bust a hose or spring a leak it is very slippery on the track. Water + water wetter is the usual way to go for that application.

While I agree that running without antifreeze is generally a bad idea for a street car, antifreeze is not the best solution in terms of actually cooling the engine and isn't even allowed on most race engines.

Your radiator is pressurized to increase the boiling point of the coolant. Even if you're just running water, you'll be able to push it way past 212 with a proper cap. Zs have 13 lb caps if I recall. According to this chart, a 13 lb cap plus atmospheric pressure of 14.7 is going to give a boiling point of around 245 degrees. Higher pressure caps are out there too if needed.

http://www.engineeringtoolbox.com/boiling-point-water-d_926.html

Edited June 8, 200915 yr by jmortensen

I did say 'under normal conditions' but I should have added that I was referring to street driven cars.

I know the thread's 7 years old, but is it possible that the OP's engine running hotter may be due to insufficient bleeding?

Do Z's even have bleeder valves? The reason I ask is because if he lost coolant, installed the heater core, topped her off, and then experienced in increase in running temperature, air bubbles may be trapped in the lines and hindering the flow back to the radiator.

He gets heat just fine, but beyond that, could this be an issue?