Drain your cooling system by removing radiator hose or bung in radiator.
Find thermostat housing unbolt and remove thermostat taking not of the way it sits in the housing, clean surface ready for new gasket pop new thermostat into housing replace gasket and use a gasket sealer and bolt back on thermostat cover.
fill radiator back up start engine and bleed cooling system make sure thermostat opens will see temp gauge move. check water level after test drive
head gasket leak or thermostate needs to be replaced
We had the same problem with our LHS. We first replaced the thermostate and it still happened. So we keep looking and the lower radiator hose was colapsing. You might check the hoses after you replace the thermostate. Hope this helps.
your thermostate needs to be replaced
locate the thermostate on the lower rad hose as it enters the engine block. Remove the 2 thermostate mounting bolts and remove the circular thermostate. Installation is the reverse of removal. Ensure you obtain a new gasket prior to installing the new thermostate.
you need to replace either your coolant temp sencor or it could be your thermostate...but most likely it the sensor...i had this prob and i just replaced both to be safe
change the thermostate
I replaced my 1996 radiator on 2006. I tried yellow pages and found a new/aftermarket one for less than $100. You might want to replace the thermostate as well. Good luck.
Thermostate
Over heating and no heat from the heater.
Thermostate on buick lacrosse
thermostate stuck open need new thermostate
Try replacing the temp sending unit. The gauge itself can go bad but seldom do.