[Supras] FW: A/C booster fans

[Jeff Mohler]

If the Rad Cap seal and/or spring is weakened, then the system holds
less pressure, leading to a lower boiling point..and more escaped
water to the overflow bottle, which amounts to less energy the cooling
system can aborb..and around you go.

However..if you dont have to worry about freezing temps, Antifreeze is
a backwards step, IMHO.

50/50 AF with water mix, has about 50% of the heat transfer efficiency
as straight water...add water wetter, and then you have the water pump
and corrosive addatives taken care of as WELL as reduced/zero
cavitation in around your cylinder walls.

If you open track your car, you should -never- have antifreeze in the
system...ever.



On 9/14/06, Eric Boeck <eboeck at cogeco.ca> wrote:
> Ahhh ...  MOST important, is that it keeps the coolant under pressure.  A
> liquid boils when it's vapour pressure equals that of its surrounding
> atmosphere.  Vapour pressure in a liquid is most often increased by heat.
> So if you increase the surrounding pressure, you also increase the vapour
> pressure neccessary for the liquid to boil, and therefore the liquid can get
> hotter without boiling.  Here's a P/T diagram for water, and you can see
> that at a pressure of 200 bar, water boils only at 374C.
> http://www.pa.msu.edu/~bauer/talks/Honnef2000/sld003.htm
>
> Also, by combining antifreeze and water, the boiling point for that solution
> goes above the 100C for water alone at standard pressure (1 bar), and it has
> to get MORE energy (heat) into it to get that vapour pressure equal to the
> surrounding pressure, and therefore boil. (check the container of antifreeze
> you used for the boiling point increase for the combination you used).
>
> Here's a link that might explain it better:
> http://en.wikipedia.org/wiki/Phase_diagram
>
> Long story short, under pressure, the antifreeze can get hotter without
> boiling.  Rad caps are designed to contain a certain pressure, but if the
> pressure gets too high, the cap releases, and THAT liquid / gas flows into
> the overflow container.
>
> As for what can break, well, I guess the spring can go soft, and that will
> release the pressure at a lower value, and therefore, the boiling point of
> the rad fluid is lower.  Any mechanic *should* have a rad cap pressure
> tester.  Just get him to test the cap.
>
> As you see in the pic I sent, the one on the far left has too small a rubber
> area to seal the big hole in the place on the rad where it goes (far right).
> The cap in the middle WILL and does seal the opening.  The cap on the far
> left is the one I got when I went to Toyota and just asked for a rad cap for
> my 91T.  The one in the middle is the brand new one, and I asked for the
> specific PART number, and NOT the cap that goes with my *car*.  The two are
> as different as night and day, and if you compare your rad cap to the pic I
> sent, and compare the opening in the rad to the one in the pic, you should
> be able to see if *you* have the correct cap.  The other way to tell is when
> the car is cold, just squeeze the upper rad hose.  If you hear bubbling in
> the overflow, your cap is either bad, or the wrong one.
>
> My car boiled over a few minutes after I turned it off because of heat soak.
> (no moving air, the heat builds up under the hood).  Since the rad cap
> wasn't keeping the fluid under pressure, it boiled at that lower
> temperature.  Now that I have the correct cap, it keeps the rad under
> pressure, and the heat soak temperature no longer is enough to cause
> boilage.
>
> HTH's
>
> Eric
> 91T
>
> PS.  Sorry for being long winded, but that's the chemist in me coming out.
> :)
>
>
>   _____
>
> From: Charismatisch at aol.com [mailto:Charismatisch at aol.com]
> Sent: Thursday, September 14, 2006 2:56 AM
> To: eboeck at cogeco.ca
> Subject: Re: FW: [Supras] A/C booster fans
>
>
> Hallo Eric,
>
> not being a professional mechanic, one thing puzzles me about your comments
> on the rad.cap. I always thought that a rad. cap was only there for 2
> reasons:
>
> 1. To get access to put more water/coolant in
> 2. To stop water/coolant spilling out of the rad. when the car is moving
>
> What can be broken on the original rad. cap or wrong with the replacement
> rad.cap on a Supra, and what is its real function? How come the car can boil
> over if it doesn't function properly, and how is it supposed to work/what
> does it do?
>
> Many thanks,
> Derek
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