Just so to be clear... When the temp indicator lights up, it doesn't mean that it's already too late. The designers aren't that stupid. In most cases, a lit warning indicator is more conspicuous than to see minute movements of the temp needle. When it initially lights up red, it means that it has reached a certain temp range beyond what the designers specified as normal (but not necessarily in the red zone). But needless to say, prolonged use in that condition is something you should avoid.