Yes, but only after it had displaced a great deal of coolant.

Jim

On Mon, Sep 9, 2013 at 4:18 PM, Tom Carchrae <tom@carchrae.net> wrote:

> Great explanation Mark.  Thank you.
>
> If the "air" is indeed steam, then wouldn't it return to liquid form once
> the system cools?
>
>
>
>
>
> On Mon, Sep 9, 2013 at 1:59 PM, mark drillock <mdrillock@cox.net> wrote:
>
> > There are 2 major choices for the "air" that appears to force the coolant
> > out into the overflow tank in your case. Either you have a hot spot that
> is
> > boiling the coolant and making steam, or you have some failure that is
> > letting high pressure combustion gases seep into the cooling system and
> > displacing the coolant. A third variation would be if you were foolishly
> > running straight water then steam is going to happen much more easily.
> The
> > coolant 50/50 mix doesn't boil until it is about 50 degrees hotter than
> > straight water does. If the cap is bad and you are running straight water
> > then that is a double whammy since a pressurized system raises the
> boiling
> > point. A leaking cap valve reduces the system pressure so boiling is more
> > likely to occur with a bad cap.
> >
> > Whether the "air" is combustion gases or steam, its source location is
> > away from the coolant tank. So when it first appears in the system it
> adds
> > rapid pressure to the system that will want to escape somehow. Typically
> > the pressure will escape through the overflow nipple of the cap and into
> > the overflow tank, pushing liquid out since that is what is in the tank
> at
> > that moment. The "air" will later end up gathered at the main tank. If it
> > had originated at the main tank it would be the first thing forced out
> the
> > cap nipple but that is not the case. Thus the source is elsewhere.
> >
> > Mark
> >
> >
> > Tom Carchrae wrote:
> >
> >> This is not a different issue - this is my cooling issue....  :)
> >>
> >> I have a question to ask the experts regarding the bad cap theory.  I
> get
> >> how the fluid ends up in the overflow tank - but if it just a cap, where
> >> does the air/gas come from the displaces the coolant - and why does it
> not
> >> pull the coolant back into the pressure tank when it cools?
> >>
> >>
> >>
>