A little story.... I was driving my G35 around Sunday evening and it started getting cold so I turned on the heat, but no heat was coming out. The engine was warm and the temp gauge showed a normal reading, so immediately that seemed odd. I cranked the heat all the way and the engine temp shot way up. I pulled over and the let the engine cool down a bit, then was able to drive home slowly with a light throttle keeping the engine in an acceptable, but still high range.
Turns out the Nisson dealer where I had service done a month ago screwed up. My G35 engine (same V6 as in several Nissans) is notoriously difficult to bleed the air from the cooling system after changing the coolant. Part of the process of bleeding the air is turing the heat on high, which never happened a month ago when I had my coolant changed. If there is air in the system the coolant won't circulate. The engine will overheat and likely cause extensive damage. If I hadn't quickly noticed the temp shoot up, I likely would have blown a head gasket causing several thousand dollars damage... and never know why.
So, how closely do you watch the temperature gauge? Would you notice if your car is overheating before damage is done? I checked, and all three of our cars have temp gauges and no idiot lights. I like having gauges, but wish there was an idiot light too just in case.