[TR] Interesting data on coolant

[spook01@comcast.net]

I was speaking with a cooling systems engineer the other day, and he was telling me some interesting facts on how coolant acts within an automotive cooling system, and how systems are designed.
When coolant is mixed 50/50 with water, the water stills boils at 212f at sea level.  The glycol portion doesn't boil at that temp, but separates from the water.  Hence, any steam in the system is 100% water, not boiling glycol.  Boilover, that is the gush of coolant out of the radiator of a hot car, is caused by this steam.
This steam, while the engine is running, can cause an insulating pressure barrier within parts of the engine allowing the metal to over temp in spots, causing pre ignition, damage and loss of power.
The hot cooling fluid reaches the water pump, where pressure changes due to pump action take place.  A steam bubble can form on the intake side, restricting coolant flow through the system.  I was told 2-2500 rpm is generally the entry point for this to happen.
If 100% coolant is used, the boiling point is raised overall to the boiling point of glycol but freeze protection is less.
Obviously, the boiling point of water rises with pressure, hence our pressure caps.  And, that's why unpressurized systems aren't used with a 50/50 mixture.
100% coolant of various types have their strengths and weaknesses.  Most are designed to work mixed 50/50 because the mixture "clings" better to the metal walls of the block/head(s) allowing better heat transfer.
The main feature of using normal coolant mixtures is this surface tension relaxation and drop in freezing point.
The first point can be proven by heating a container of 59/50 coolant mixture to 212f or so, and collecting the steam on cool metal.  It's water!
This guy said that the normal mix is used for corrosion control, slight improvement in cooling efficiency, and, mostly, for freeze protection.  He talked about about additive packages being different for different types of coolants (long life, etc.) and how some can interact.

I also asked him about waterless coolant, and he said it was too expensive for use in mass produced autos, but did offer significant advantages in boiling point and going pressureless in systems which equates to longer hose and pump life.
Interesting, eh?

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