There are also many cases where a failing alternator that still puts out 11-12 volts
will allow the car to run but will cause other things to not work. I have personally
seen a suburban that completey shut everything down (cluster, guages, power
windows) except the engine. Last week a dodge neon had all the cluster lights on
and the car was stuck in first gear because the alternator was at 11.6V instead of
13.6+. As far as the coolant goes like tom said get a second opinion on everything.
if anywhere ever gives you a price of $150+ and its not something you are educated
on, get a second opinion.