[TR] Interesting data on coolant

[Anthony Rhodes]

 Hmmmm, there may be a difference between evaporation and "boiling" with
regards to the combo of water and glycol coolant. Certainly there will be
water evaporation at a higher rate than glycol evaporation from a hot mixture,
but I am pretty sure the boiling point is raised above the boiling point of
plain water.  It may be true that when boiling of the mixture finally occurs,
most or all of the vapor is water, not glycol

The gush when opening the pressure cap is due to the fact that, as you said,
pressure further raises the boiling point. When you remove the pressure,
formerly non-boiling fluid may start to boil.

So, I don't see your info as being fundamentally different from the general
understanding people may have had before, but I do disagree with the idea of
the temperature of the boiling point not changing compared to plain water.
That said, I have not tested this personally!.

-Tony

Sent from my iPhone

On Mar 2, 2014, at 2:00 PM, triumphs-request at autox.team.net wrote:

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> Date: Sun, 02 Mar 2014 12:33:10 -0600
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> To: "triumphs" <triumphs at autox.team.net>
> Subject: [TR] Interesting data on coolant
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> 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?