Chevrolet Repair: overheating, head gasket, monto carlo

Question
i have a 1996 monto carlo 3.1    wants to over heat  temp gauge goes up and down when driving   already changed the thermostat    no sign of head gasket leaking     the antifreeze bubbles in the over flow tank   could it be the temp sensor?    it has 124,000 miles

Answer
Hi Brian Bell,

Your temp sensor is working if it is telling you your motor is hot.  You have 2 fans.  One is the low, and the other is the high cool.  One will only come on when the a/c is on max or the engine has gotten too hot.  It is to assist the usual fan.  

It is possible that the low fan is not comming on.  Check to verify that.  If not, that could be a fan switch.  This could be faulty or because the coolant is low.  

I suspect the radiator is old and plugged up.  It gets hot, kicks on the high fan, and the temp comes down.  Try flushing the cooling system to see if it helps.  Also looking for rusty water.  Pull the thermostat first, so debris doesn't get in it.  If this helps a little or not at all, replace the radiator.  

C J S