Originally Posted by Efthreeoh
This is backwards. The T-stat will throw a code and will illuminate the SES light, so you will know when it goes bad. But "going bad" only means the heating element has failed in it, the t-stat will still operate properly. The only way to "keep an eye" on the waterpump is to scan the ECU for shadow codes that indicate a slow waterpump speed, which do not illuminate the SES. Once you find the code for a slow waterpump it means the pump is on the way out.
Thanks for the correction!