I really meant that only having the light won't show you what's going on. I agree that having both is ideal. Reading up on my Territory, that when the temperature goes to high, It will beep at you, then if you ignore that, then it starts cutting out cylinders, until you don't have any power. So hopefully you pull over and see whats going on. Having worked for the RAA for many years. It's amazing how many people keep driving, with the light on hoping to either get home or that things will get better by themselves, until the engine seizes up. One member had a faulty alternator, so I gave it a tap with a hammer, and it started charging. Usually worn brushes. A week later, he still hasn't bother fixing it, but kept hitting it until he put a hole in the side of the alternator.
JD