All are good suggestions. Start as ink said some will throw a discreet fault with no light. If you need a thermostat, I personally go back to oem on my vehicles due to several of the after markets failing shortly after installing. If as stated the temperature isn't where it should be it will mess with the system. Even if the guage is about where it normally runs. The O2 sensors usually from my experience won't give a light unless the heat circuit is failing. As far as O2 sensors go buy NTK (ngk) direct fit. The one I bought for my Durango from Mopar was made by NTK who is also NGK. It was stamped right on the sensor.
