If you have substantial coolant being forced into the overflow and
replaced by "air", the "air" has to come from somewhere. The choices are
either a hot spot boiling the coolant and making bubbles or combustion
gases getting into the cooling system. A leak in a sealing ring at the
top of one of the cylinders can allow combustion gases to pass into the
water jacket.

I assume you are using a 50/50 mix of water and coolant. Plain water
will boil at a very low temp and cause problems. Also the pressure cap
needs to hold pressure. Does it? (it should hold 15 psi +-2 psi though
checking this is not simple) From your problems with rear heater leakage
I would guess you have too much pressure not too little. This makes
combustion gases seem the more likely source of your problems.

Mark

kevin obrien wrote:
>
> Hello All (Again!)
>
> I'm out trying to bleed the air out of my 1990 Carat's
> coolant....did the procedure (per Bentley)
> yesterday....seemed like air was out.  Took for 20
> mile drive (mostly flat and downhill) ....temp good
> (needle 1/2 way to a hair above red light....which
> continues to blink by the way , despite a new sensor.)
>
> Anyway...coming home (long gradual uphill) temp climbs
> gradually to 3/4 up gauge...getting hot.
> Shut her down up rgetting home.
>
> Today....begin Bentley procedure again...notice
> Overflow Bottle (behind license) is way above "Max"
> level.  Begin procedure...radiator bleeder
> open...girlfriend is keeping engine 2200-2500
> rpm....keep adding coolant as it drops in Expansion
> Bottle...seeing a little flow out radiator bleeder and
> small bubbles....
>
> Accidentaly unscrew bleeder too far...bolt & washer
> fall out...girlfriend is revving engine..coolant
> shoots out of Rear Expansion tank.   Shut her down...
>
> I get bolt back in....fire her up...radiator bleeder
> is open...no sign of flow. After awhile coolant begins
> shooting out of Expansion bottle (seeming to blow back
> into bottle from upper hose (the big one...not the one
> to the Overflow.).  Shut her down...
>
> Pissed...defeated...I return to The List.  Any Gurus
> out there know what is going on???
>
> Thanks
> kevindobrien@yahoo.com
>
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