Is it possible that your head gasket is leaking combustion gases into the
cooling jacket?

Entity Chas Hoakanson spoke thus:

> Need a little more help folks:
> I posted this morning that when I got to work I noticed the coolant boiling
> in and out of the overflow reservoir.  After work, I went out check the belts
> and such -- all okay.  I  replenished the coolant in the overflow reservoir
> (with some bottled water since fortunately my wife had just gone to price
> club abd left a case of bottled water in the van) and drove home (abot 26
> miles of mostly freeway).  Temp was fine (stayed below the LED).  However,
> about half way home the LED started blinking and statyed blinking the rest of
> the way home.  Owners manual says this means the coolant is low.  Checked the
> overflow and it was full, and totally cool.  Of course the coolant in the
> main tank was hot and appeared full (hard to tell)  Belts are fine, since it
> doesn't overheat the thermostadt must be fine, no obvious leaks.  I haven't
> openned up the cooling system or anything for over a year. Kinda stumped  --
> any help appreciated.  thanks