Chevrolet Repair: Overheating

Question
I have a 2006 Chevy Equinox FWD 3.4 V6 automatic with 136K.  It recently started overheating.  I pull over, shut it off until the fan stops.  It drops back, according to the gauge to less than halfway and starts to climb again.  It happened the other day when it was 25 below, and happened again today in the +50's.  Was some slow moving on back roads and had no highway trouble.  Suggestions.

Answer
HI JIM,,WELL THE FIRST THING I WOULD DO IS LET IT COOL DOWN AND THEN CK THE [RADIATOR LEVEL] NOT THE RESERVOIR...MAKE SURE IT IS FULL WHEN YOU REMOVE THE CAP..IF NOT, START IT AND WARM IT UP AND REFILL USING GM DEX-COOL. IF IT IS REALLY LOW HAVE IT PRESSURE TESTED AND CK FOR A LEAK..IF JUST 2 QTS LOW OR SO THIS COULD BE NORMAL..BUT LETS SAY YOU CK THE RADIATOR AND IT IS FULL.YOU SAID IT GOT DOWN TO -25 DEGREES..MAN THAT IS COLD..I WONDER IF THIS COOLANT HAD FROZEN A BIT..NOT GOOD. YOU MAY WANT TO CK FOR HOW LOW THE TEMP IS PROTECTED IN THE MEAN TIME JUST TO BE SAFE. BUT IF THIS COOLANT IS GOOD AND FULL AND CLEAN THEN YOU MAY HAVE A HANGING UP THERMOSTAT.
IF IT WERE MINE AND ALL OF THE ABOVE CKS OUT,, I WOULD PUT A NEW T-SAT IT IT JUST TO RULE IT OUT.
YOU SAY THE COOLING FANS ARE RUNNING SO WE CAN RULE THIS OUT..THE FANS SHOULD STOP ANYWAY WHEN YOU DRIVE OVER 35 MPH..THERE IS ENOUGH AIR GOING THROUGH THE RADIATOR AT THESES SPEEDS. NO NEED FOR THE FANS..SO LAST THING AND YOU ARE NOT GOING TO LIKE THIS AND THAT WOULD BE A BAD HEAD-GASKET. LEAKING INTERNALLY,THIS WILL CAUSE OVER HEATING PROBLEMS FOR SURE...BUT,, CK THE ABOVE OUT FIRST AND REPLACE THE STAT AND KEEP YOUR FINGERS CROSSED..I HOPE THIS HELPS YOU AND VERY GOOD LUCK TO YOU SIR..TOM..