djhedges
Active member
Our bug threw the engine code P0128. My initial reaction was it's a bad thermostat. I read several forum posts criticizing mechanics for swapping a thermostat without verifying it wasn't the coolant temp sensor. It got me thinking how do you verify it's a bad thermostat?
My biggest indicator was that I could drive the car home with the heat on full and not want to take off a jacket. It wasn't that cold of a day either. I also logged the coolant temp data with a bluetooth ODBII reader and graphed the results.
https://docs.google.com/spreadsheets/d/1mtmV44TQO5UZyrp7oTAHY4ssI-ynyk_Ul2YIZyi2RUk/edit?usp=sharing
You can see the coolant temperature peaked at ~72C on the interstate while driving home with the old thermostat.
The new thermostat reached ~90C on interstate. I believe the thermostat opens at 87C. Also note the lower air intake temps on day I measured the new thermostat.
My biggest indicator was that I could drive the car home with the heat on full and not want to take off a jacket. It wasn't that cold of a day either. I also logged the coolant temp data with a bluetooth ODBII reader and graphed the results.
https://docs.google.com/spreadsheets/d/1mtmV44TQO5UZyrp7oTAHY4ssI-ynyk_Ul2YIZyi2RUk/edit?usp=sharing
You can see the coolant temperature peaked at ~72C on the interstate while driving home with the old thermostat.
The new thermostat reached ~90C on interstate. I believe the thermostat opens at 87C. Also note the lower air intake temps on day I measured the new thermostat.
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