DealerShip Service or Kmart?

[MattW]

coolant isnt really antifreeze or antiboil. It just raises the point at which it boils and lowers the point at which it freezes. A glycol coolant actually inhibits the transfer of heat from the engine to the coolant, but it doesnt boil because of the raised boiling point.

[Tommo]

Ummm.
I use a 'coolant' which is mainly ethylene glycol.
true enough, the specific heat capacity of 100% eth. glycol is only about 60% that of water (depending on it's temperature). 50% eth glycol has about 80-85% of the specific heat capacity of water. this is the solution's cooling capacity, if you like, and means it isn't as good at cooling as water is. Mind you, even at 100% pure it's about the same as engine oil, for example. It just happens that water is one of the best 'coolants' around inside it's operating temperature. So a 50/50 mix is great for cooling, but it will allow rust, unless your 'coolant' has some anti-rust additives, which many do.

As for eth.glyc. not being anti-freeze, a 50/50 solution of eth glycol and water freezes at about -37 celcius, so I reckon that counts as antifreeze as much as anything does. I've been in -12 up in the vic alps, and my car worked fine even after sitting overnight and ending up under a metre and a half of snow. (For those smarties out there, yes - i realise a snow blanket would partly insulate the car from the -12 outside, but i did brush it all off and then leave it for a while too...)
A 50/50 solution also boils at about 107 celcius.

Eth glycol also has a much lower surface tension than water, which aids it's ability as a coolant.

Eth glycol is also about 10% more dense than water, so even though it has 40% lower specific heat capacity, this is partly offset. If it does boil, its vapour pressure is much lower than water... to the point that if you filled your radiator to 100% with it, you could drive around with the cap off. (No, Don't try it.)

So water has the highest surface tension, lowest specific gravity, and lowest boiling point... it's not ideal as a coolant, even if it has a high specific heat capacity.

When you add up all the elements and put them together a 50/50 water/glycol mix, plus an added surfactant, and a rust inhibitor, is the best coolant mix. You can buy it already mixed in a bottle at most auto places. But pure water is not the go.

[krankieone]

Dont forget boiling point increases with preasure

Ummm.
I use a 'coolant' which is mainly ethylene glycol.
true enough, the specific heat capacity of 100% eth. glycol is only about 60% that of water (depending on it's temperature). 50% eth glycol has about 80-85% of the specific heat capacity of water. this is the solution's cooling capacity, if you like, and means it isn't as good at cooling as water is. Mind you, even at 100% pure it's about the same as engine oil, for example. It just happens that water is one of the best 'coolants' around inside it's operating temperature. So a 50/50 mix is great for cooling, but it will allow rust, unless your 'coolant' has some anti-rust additives, which many do.

As for eth.glyc. not being anti-freeze, a 50/50 solution of eth glycol and water freezes at about -37 celcius, so I reckon that counts as antifreeze as much as anything does. I've been in -12 up in the vic alps, and my car worked fine even after sitting overnight and ending up under a metre and a half of snow. (For those smarties out there, yes - i realise a snow blanket would partly insulate the car from the -12 outside, but i did brush it all off and then leave it for a while too...)
A 50/50 solution also boils at about 107 celcius.

[Tommo]

True.
But if 50/50 boils at 107 (roughly) at sea level, then a little vaporised water will bump up the pressure even more, further retarding boiling.

If you used 100% glycol, the boiling point would be almost 200 celcius anyway. If it does boil, it doesn't expand anywhere near as much as water though, so the increase in pressure is less to retard further boiling. So if you are running a cooling system in which the coolant runs cooler than 200 you're fine with pure glycol.

Oh, and when I talk about pure glycol, you probably want to use it in an aqueous solution anyway because pure eth glycol is flammable.

It's also poisonous, so if you think you might have to drink it, use prop. glycol instead.

[mjy78]

Well I ended up taking the Jeep into Footo's at Sumner Park and I must thankyou all for the suggestion! I'm very happy with the service and the price was excellent. I think it's safe to say the Jeep service centre won't be seeing much of me anymore.