I recently flushed the coolant, changed oil, resolved oil pressure issue, and several other things. Car is running great! thanks to all who advised...

Now I'm getting P0128 code. Interestingly, temp gauge isn't getting up to the normal position, straight up, but rather a little below. The heater is working great, coolant level is stable, double checked for air in coolant system by trying to burp it (no air came out), the fan doesn't run after shut off, and I'm not getting any codes.

Before I start blaming the thermostat and replace that, and all that goes with it, I was wondering something. If the thermostat is stuck open, could it actually run on the cool side? Do I understand correctly that a thermostat isn't just "open" or "closed", but can be somewhere in between according to the temp of the coolant?

Could it be the coolant temp sensor and if so, how do I troubleshoot that one?

Thanks,
Monty

 

the tstat should open around 97 C. before that you will not have heat in the top front hose if its working properly

yes failed tstat can cause low temperature

 

Had this code few months ago. Just a stuck open thermostat. Make sure to replace it with a reputable brand. The sh¡t on Amazon doesn't last more than 1-1.5 year. Also, one of the bolts broke off when putting back the housing together. I didn't apply much force. Luckily, I was able to remove it with pliers. Probably best to buy new bolts.

 

as everyone already said, a stuck t-stat would prevent the car from getting up to temp properly. however, if it was all good before you did some work on it and now this is a new issue, i would double check all my previous work, first. secondly i would replace the sensor.

 

Yupp! I changed it out and all's good. Thanks for the insight guys.