I change the thermostat and now need to reset the engine light. Was wondering how that is done?
You need to read the trouble codes. Where are you located?
Scan your vehicle to verify if P0128 is the only code present .If others codes are present they must be addressed first.
If the code is P0128 will clear itself after 3 trips where the set condition does not exist.
The way it varies temperature is by controlling the flow of coolant into the vehicles engine, in regard of thermostat of vehicle. Engine light will come on if you are not changing your coolant regularly.
Have your issue resolved?