I would throw a thermostat at it iregardless of that reading...I've very seldom (if ever) saw a 128 be anything else but a thermostat...jerry

 

Gave the nuts on the thermostat housing a tug and broke my 1/4" extension.
Headed to AZ for some vacuum hose so I'll pick up a 1/4-3/8 adapter. I'll need it for the sensor too, if the stat idea doesn't pan out.

 

Thermostat

 

I think it might be time for a cooling system flush.

 

Definitely. Water is black, might be the Dexcool but I think it is coming from the black hoses. Can't figure how to detach the Lower Radiator hose to do it.
The stat opened at 195-200 so for now I'll reinstall it and keep trying to remove the sensor,

 

$2.69 and up @ Rock Auto....Why would someone go this far and put it back in? Vehicle ran @ 150 degrees.... I would install a t/stat, drive it and see if the code (PO 128) comes back.......but if one enjoys additional work...pull the sensor and perhaps you can flush it thru that hole...

 

Ok, I got a new thermostat and put both of them in the stove water and They both opened at 195. However the old stst opened twice as much as the new one, which may be the reason the car ran so cool.
Put put the new one in and drove 20 miles today. At the end of that run the non-contact thermometer gave me a reading at the thermostat housing of 201.
Not sure what it all means.

 

What was the non contact thermometer reading at the thermostat housing with the old thermostat installed?


George

 

And what was the temp gauge reading? I've never heard of the sensor failing but I have heard of the gauge being off.

 

I had a sensor fail. Seen that before.

Testing your thermostat is always a good practice, also the easiest for troubleshooting.
That old thermostat opening double of the new one - broken winding on the spring maybe?

Usually they fail the other way round and don't open enough.