overheating

my 92 v6 is overheating in a very odd way.
the temp gauge read hot and the heater went cold, my thougth was low coolant or bad thermostate. I changed thermostate and topped off radiator and replaced the temp sending unit (prior ower claims to have replaced waterpump, radator and timing belt) After my changes still same issues. The engine seems much cooler than gauge would indicate. the radiator is only slightly warm to touch, hoses are warm but not hot and engine is warm but not hot, yet gauge is reading max hot. I ran with rad cap off to burb system and changed cap. now will either run cold for the 30 miles I commute or will warm when sitting at stop lights. if engine temp gauge reaches above the 2nd mark above cold it will continue to hot. and yes the fan will turn on eventually with little effect on temp gauge.
no coolant leaks visable, no oil in coolant or coolant in oil. ideas?

had a mechanic presure test the system and look for issues, he could not find any. I did find what may have been part of the problem. the heater thermostate is very sticky from sitting. I moved it several times and the heat eventually got better and the engine temp reduced. I then re-burped the engine by running it for some time with the cap off and was put in about another quart of coolant ( the mechanic put in a quart also) Now the engine runs cold but consistant (cold because no engine thermostate) and the heat is consistant. I belive the heater core was unfilled with coolant due to a stuck or sticky heater thermostate and would create a low coolant and air bubble situation.

more investigation shows valve idea wrong. the heater control valve is vacuum activated. I did find that if I accelerate the engine temp drops and the heater puts out heat. new idea is I have a faulty heater control valve and when the vacuum drops it allowes the hot water into the heater core which acts as a secondary radiator, cooling the engine. this leads me to believe I have a faulty radiator. I will need to test the valve, vacuum lines and likely replace valve. then have the radator tested.

arg! I hate this car!. the heater control valve was not where the picture said it should be (drivers side next to the power brake booster) either someone took it out our it is some place else. I have a 92 v6 anyone know for sure what the valve is?

as much as I wanted it to be something else it was the head gasket. the prior mechanic had not tourqued the head properly or added the correct amount of coolant, a double whammy. the heads were warped some but able to be trued up, thankfully no cracks (heads are another $200) word to the wise, make double sure the heads are properly torqued, (right ft/lbs and correct order):uhoh: