okay i have a 95 blazer . when i got it it was overheating . found water in floor and thought it was the heater core . turned out the rad was stopped up from failure to maintane dex cool . so i changed the rad flushed the system and ran it with the heater core bypassed . well just had new born son thought might be a good time to fix the heat . flushed the core and hooked it back up and made sure there was no air in system . now my temp gauge goes up to bout 215 and drops to 190 and keeps doing it while driving / i stop in traffic 215 as soon as i take off 190 and then will slowly climb and then drop while steady driving . not sure whats causeing it . did not happen till hooked heater core back up ????? any help ? thanks .

 

Too many things to type right now & I'm not blowing you off but try the Search feature.
Tons of things like this have been covered, thermostat, air bubble, clutch fan etc.
Plus it gives you reason/excuse to "get away" because it's about the DD lol
(don't show the wife this!)

 

Sounds like an air bubble to me, but like the above post said it could be several things.

Can you hear the clutch fan kick in when it gets hot or on first start up, by hear I mean the "roar" of the fan? If not then your fan clutch maybe bad.

You could also be having a sticky thermostat, you may want to also check your coolant level as well.

 

It could be the temp sensor / wiring / connector. Mine Opel car had a worn out connector and have a similar behaivor.
Also air bubbles: a Renault car that I had, have the same issue (related to a worn out water pump).
And another Opel car (just 30.000 miles) had a bad thermostat and similar behaivor prior to thermostat failure.

Air bubbles doesn't came alone: normally when temperature raises, water turn to steam and appears air bubbles. Is not solved the main problem, you should have more and more bubbles and, eventually, you need a new engine.

First check for water coolant leakage. If not, check the thermostat operation checking the temperature between inlet and outlet radiator houses when you get around 190 °F. if one is cold and another is to hot, bad thermostat. Also check for temperature switch/sensor.
Sometimes a worn out cable/connector/sensor gaves erratic signals. Check also for melted or dirty connectors. Remember to put electrical connector cleaning and then dielectric or tune up grease (is the same) in connector for a long life.
Sadly I dont have any problems with this issue up now with mine blazer, so I cannot gave you more info.

Good luck