Water temperature has dropped to about 150° and stays there. SES came on, P0128.
because the temp does not rise to normal i'm thinking it's a bad sensor. Am I thinking right?
Okay, now where is it?

 

Try pulling your thermostat and see if it wide open first. When they fail, they fail in the open position and will cause low coolant temps. Cheap and easy fix if that is the problem.

 

I was thinking when the thermostat is wide open the temp holds at 195, not 150, so I figured an open thermostst was not the problem.

 

You would be incorrect. It does sound like a bad thermostat. Do you have a non-contact thermometer? If you do, verify that the engine temp is actually 150 degrees when it's warmed up. If it is, replace the thermostat.

 

I had this happen a while back. It was the thermostat.

 

Thanks, y'all, good idea with the noncontact thermometer. I used it and temp at stat housing was 193.So it must be the sensor? Which one and where is it?
Thanks in advance

 

Driver's side head near rear spark plugs

 

Holy cow what a bitch to get out, IF POSSIBLE.I wish it WAS the thermostat. I'm quitting for now, the sensor is still in there but so is the coolant(!) so at least I can drive.

 

Soak it with wd. And try after the engine is warm, it might break loose easier.

 

Got to get a wrench on it first. It's way down in there.