thermostat still fluctuates after replacing new one.

i just replaced my thermostat in my 1990 chevy silverado because everytime i started it the temp gauge would go to 210 degrees then back to normal. now my temp gauge gets to 170 and drops back to 150 then up to 170 with about 30 seconds in between intervals. i also notice bubbles coming up from the hose in the reservoir now after changing my thermostat and adding coolant to appropriate levels..(no bubbles came up with the previous thermostat). i can only assume air bubbles in the radiator.

i just replaced my thermostat in my 1990 chevy silverado because everytime i started it the temp gauge would go to 210 degrees then back to normal. now my temp gauge gets to 170 and drops back to 150 then up to 170 with about 30 seconds in between intervals. i also notice bubbles coming up from the hose in the reservoir now after changing my thermostat and adding coolant to appropriate levels..(no bubbles came up with the previous thermostat). i can only assume air bubbles in the radiator.

you have air in the coolant system . with the pressure cap off idle engine and add coolant until full.

the temp should be solid 190 deg f area. 210 too high 170 too low.

cold engine may over temp then drop down. like 210 then drop hold at 190 deg.

okay. thats what ive been told before and i tried that. i ended up putting some coolant in the radiator until it was full but its still doing the same exact thing of bouncing between 170 to 150. maybe something is wrong with the sender. Im hoping and praying not a head gasket...

okay. thats what ive been told before and i tried that. i ended up putting some coolant in the radiator until it was full but its still doing the same exact thing of bouncing between 170 to 150. maybe something is wrong with the sender. Im hoping and praying not a head gasket...

the temp should be 190 deg f not 150.. so some how the coolant is going around the T stat. you installed this correctly and used the proper T stat ?

should be a rubber gasket on the outer edge of T stat .. many times cheap T stats do not work properly but this is the exact same issue so must be a install issue...T stat must fit into the bore tight...........

head gasket will cause the coolant to boil. this then is air the water pump pumps only water not air this causes temps to rise as the air increases and stops the coolant flow................

if you have good heat then the sender can be bad.. I have a temp reader that measures at the goose neck with these type issues ..

Reading your 1st post, I would have to say that the original T-Stat was good and doing what a normal OEM 195* one would do. It sounds like there is still air in the system and you've got a 160* stat in now?