ok so im driving home from work and i notice the car is reading 4 bars...thwn goes to 3...then goes to 4...then five..then 4...then 4...then 4 then red. i pull over done notice any leaking..nothing under the car nothing. let the car cool down get home and park it..checked it again same thing.. i get a code and it reads P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature). A code P0128 may mean that one or more of the following has happened:

Low engine coolant level
Leaking or stuck open thermostat
Faulty cooling fan (running too much)
Faulty coolant temperature (ECT) sensor
Faulty intake air temperature (IAT) sensor

my levels are fine. rad. is getting hot top hose getting hot. bottom is warm..seems fine..cant put my finger on it but can be faulty thermostat or water pump?

please help.

 

Is the heat good and hot? Rad is full yes?

 

heats never been hot

 

You got the CEL because the car got too hot and it locked your thermostat open, need to replace it.

Also he asked you if the HEAT is hot. He's basically checking if your heater core is full (aka it's been bled properly when filled last)

 

Heat in the car should get very hot when set to do so.

If it doesnt, you likely have air in the system. This will surely cause overheating.

 

well i think if ur thermostat was stuck open it would have symptoms like if u didnt have one at all...never comming to operating temp...stuck closed or sticking will cause to overheat...test it....also test the other compenents with a volt meter...but with the ECT as the temp gets hotter the voltage goes down on it cuz its an NTC type sensor....