Thermostat stays closed

[Shassan]

I recently took my 03 Matrix XRS for emissions and failed due to P0128 OBD code pointing to a thermostat issue. My Matrix was running terrific but I decided to change the thermostat. When I removed the old thermostat I noticed that only part of the thermostat was there. The springs and copper were removed basically leaving the thermostat open. I put the new thermostat in and put everything back but now my Matrix is overheating. I suspect that the thermostat isn't opening. I am not sure what to do next...the service manual diagnostic for thermostat calls for me to change the ECM unit now. Any suggestions?

[fishexpo101]

Did you reinstall the thermostat with the jiggle valve pointing up? There is a little dot or arrow that indicates how the thermostat should be installed, otherwise it may not open correctly.

Running an open thermostat from before, assuming this was done by the previous owner, actually would have cause more issues with overheating. Only thing I'm worried about is this was done to cover up a previous issue / problem with the car.

[circuitsmith]

Did you put in an OEM (from Toyota) thermostat? Facing the right way?

Does the cooling fan come on?

If the top hose and radiator stay cool when it overheats then the thermostat is staying closed.

Check the coolant temp sensor, it might not be really overheating. Any boilover or loss of power?

[Weanuts]

Boil the new and the newer if purchased in some water with a thermometer on board. Bad thermostats are out there.

[Shassan]

I figured out the solution by doing a compression test on the radiator cap. Turns out all I needed was a new cap for the system to hold pressure enough for the thermostat to open and close. Thanks for the replies, tjis is a great forum.

[shortlid]

yes they can be bad out the box!