HELP!!!! Cooling Problem

[tturse@ps-b.com (Thomas Turse)]

Hi all, just a quick question about a recent cooling problem I've been
experiencing.  The other day I was driving up to Pikes Peak and my car
started overheating and coolant was leaking everywhere.   I pulled over and
opened the hood, when the car cooled and smoke cleared it seemed that the
coolant was spraying from under the filler cap.  This has never happened
before and the outside temp was only in the 60's.  I let the car cool and
refilled the radiator w/ water.  After letting the car run at idle for about
15 minutes, the car was at normal operating temp so I drove it around
Manitou Springs for a while and no leaks or overheating.  I cautiously drove
back to Evergreen.
    The next day I drove around the mountains for a while and everything was
normal.  Then yesterday driving home form work in Denver, the temp gauge
started to raise to the upper 3/4 mark on the gauge and sure enough steam
started to pour from under the hood right at where the filler/resivour is
located.  I checked the cap and everything seems normal.  Also, The symptoms
are:  under normal driving conditions and consistent outside temperature
range the temp gauge will abnormally move to the upper marks of the gauge,
w/ no warning light coming on.  Then  steam and coolant leak from the
vehicle, seemingly from the filler cap.  There don't seem to be any other
cooling system leaks when the car is cold/parked- no drips at all. The
problem seems to only occur when the system is hot/under pressure and I
can't explain the sudden increase in the temp gauge just minutes before the
overheating occurs.  Any suggestions or thoughts on this problem would be
greatly appreciated.

Sincerely,
Thomas C.  Turse
tturse@ps-b.com
85 4ksq   141,000