Antifreeze

[STAG GEEK Mk.1]

I am thinking about changeing my coolant to a 50/50 mix of Prestones anti freeze and ironised water? What do you think ? thank you Martin

[GDPR]

30% will be more than adequate, and 50% would be more viscous and I don't think will circulate as well.

Why 50%?

[wilf]

Being a lazy b, I have always used a 50/50 mix on various cars (easier to measure) with good results.

[Staggard]

30% will be more than adequate, and 50% would be more viscous and I don't think will circulate as well.

Why 50%?

The way I understand it is the higher the antifreeze content the better the corrosion resistance but lower the cooling properties and vice versa

[NickA]

The way I understand it is the higher the antifreeze content the better the corrosion resistance but lower the cooling properties and vice versa

Which is why I only add 25% anti-freeze!

[V Mad]

The way I understand it is the higher the antifreeze content the better the corrosion resistance but lower the cooling properties and vice versa

Agree. Water is over twice as good at cooling. Another thing, antifeeze expands much more, which may cause over pressurisation. Because of this I only use 25% antifreeze.

(I can feel another debate coming....)

[wilf]

But I have a header tank with lots of room for expansion...............

BTW, this cooling effect thing. Does anyone know in what respect antifreeze is "less good" at cooling than good old H2O? Is it to do with some form of heat capacity or wetting ability?

[V Mad]

I believe it is the Specific Heat capacity.
Water=4.19 (kJ/kgK)
EG=2.36

[wilf]

Great. Understood.

But does that not mean that for any given amount of heat transferred from the engine metalwork to the coolant, the temperature of the water would rise less than the temperature of an equivalent amount of EG?

And, the amount of heat "rejected", or transferred to the air, by the radiator depends on the difference in temperature between the air and the coolant|? In which case a higher coolant temperature will lead to a greater amount of heat transferred to the airflow, all other factors being the same?

I can feel another headache coming on.

[KOY 23]

Agree. Water is over twice as good at cooling. Another thing, antifeeze expands much more, which may cause over pressurisation. Because of this I only use 25% antifreeze.

(I can feel another debate coming....)

Surely the pressure cap limits max pressure??

[V Mad]

Great. Understood.

But does that not mean that for any given amount of heat transferred from the engine metalwork to the coolant, the temperature of the water would rise less than the temperature of an equivalent amount of EG?

And, the amount of heat "rejected", or transferred to the air, by the radiator depends on the difference in temperature between the air and the coolant|? In which case a higher coolant temperature will lead to a greater amount of heat transferred to the airflow, all other factors being the same?

I can feel another headache coming on.

For the time being Wilf I am going to pass on that. I dont want to get my self in hot water. lol

But if you want to get a headache, have a look at this website: http://www.engineeringtoolbox.com/ethylene-glycol-d_146.html

It says:
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.

[wilf]

Chris, that would make sense, but something is telling me that the actual amount of fluid circulated isn't a limiting factor for most engines, in fact there is a school of thought that says slowing coolant flow down actually increases heat pick up and transfer capability.

Like you, I think I will stop worrying about it, for me, so far, my "shade tree mechanic" 50/50 mix works well enough, and I guess that is really all that matters.

[Stag therapy]

I am neither a chemist nor a physicist and it is some years since I was in school, but I would imagine it is to do with the molecular structure of the liquid.

Molecules move around in a liquid. As water is heated, the space for the molecules increases until it reaches boiling point when the molecules break away. Additives such as ethelene glycol will interfere with this process making the water more viscous, thus lowering the boiling point. The same additives also prevent the molecules coming together so easily when water reaches its freezing point.

Given the source of the heat is constant, the heat either stays in the liquid or it is transferred elsewhere.

If it stays in the liquid, whilst the boiling point will be increased over unadulterated water, it will become hotter, with a consequent increase in pressure until that boiling point is reached..

If the heat is to be transferred elsewhere, with the increase in viscosity, in order for the same amount of heat to be transferred as if there was no additive, there has to be an increase in the circulated volume.

To take an extreme example, if you were to fill your cooling system with molasses, you would instantly achieve a higher boiling point than that of plain water, but because of the higher viscosity, the amount of heat transfer through the radiator would be affected considerably, as the volume of liquid being cooled by the fins, would be affected by the viscosity of the molasses.

The recommended %ages for EG are probably a compromise between increased viscosity and the attendant problems, its anti corrosion qualities, but also the performance qualities of the anti freeze.

Baz

[Jeff]

Just add salt to the water, that lowers the freezing point

[V Mad]

Salt? Molasses? How about some yeast, and make a brew?