Temp reads from 140 to 200 then stabilizes then changes all over the place slowly then when parking here bubbling.  Haven't even opened hood its hot here in Vegas will check things this weekend. ideas about temp gauge?

|UPDATED|6/29/2016 9:27:40 AM (AZT)|/UPDATED|

When cold, make sure the cooling system (including the heater core) is purged of all air & all parts of it are full to required levels including the coolant recovery tank.

just checked and there the  radiator needed a cup of coolant of course over flow tank is never full, just realized somehow the radiator cap was changed to 7 llbs  thanks for replying, more after testing

|UPDATED|7/10/2016 1:42:28 PM (AZT)|/UPDATED|

The specification on the radiator cap should be 15 or 17 Lbs depending upon the year & engine of your car.  Check the specification in your owners manual.  You should also ask the question why only a 7 lbs radiator cap was there in the first place.  I recommend an AC Delco or Stat replacement.

Why do you say "of course"?   Your coolant reservoir should be about one third full, and the radiator should be 100% full with a cool engine.   As the coolant in your engine heats up, it expands, and the excess will flow into the reservoir..   As the engine cools off, the coolant will contract, and the coolant in the reservoir will be drawn back into the radiator, thus keeping your radiator 100% full.   This presumes you have a good radiator cap!

That is why I said of course the reservoir is not full. I left cap off after filling and it went down a little over night no leaks and engine is new hope it was just settling. will test tomorrow

Left cap off reservoir, or left cap off radiator?   What went down?   Having trouble understanding what you're trying to say.

Left cap off radiator over night to observe and it was lower, we are repeating this and it is still lower at radiator then after testing all day it stayed at the top, put cap on and drove it seemed better however when accelerating and warmed up temp gauge would still dip 20 degrees however at  idle or at constant speed temp would stay constant, still checking or air pockets, new plan to idle with cap open at a incline so it will help purge? Waiting for cool off this morning to test level.

|UPDATED|7/13/2016 8:15:17 AM (AZT)|/UPDATED|

Does your car have a bleeder screw on the thermostat housing?

No it does not temp is OK I think temp gauge is erratic when under normal acceleration is drop substantially waiting to cool down this morning to check connection on sending unit