At a certain moment the cars were fitted with a meter to monitor the temperature of the coolant. They were usually provided with a scale and a color. Red or H from hot meant that the temperature was too high and that it had to be stopped to see what was going on.
Of course you could also continue driving while the meter was in the red area, but that would ultimately not be good for the engine. It almost always leads to a broken head gasket and when driving for a long time also to a bent head or even a bent cylinder block. In short, an expensive repair that could have been avoided by keeping an eye on the meter. When you see that the gauge is running, turn on the heater blower and open the heater valve. Stop in a safe place as soon as possible and see what happens. But there doesn't always have to be a cooling problem. Years ago I heard from someone that his classic English car was constantly getting too hot. Everything had already been replaced. The thermostat, hoses, radiator and water pump were renewed and the problem remained. In the end the meter turned out to indicate too much! The same happened to me in the eighties with a Volvo 240. Driving on the highway the temperature gauge suddenly rose to a terrifying value. However, when I pulled up and opened the hood, there were no signs of overheating. Back in the car I started the engine again and saw that the fuel gauge also indicated much more, even though I had not refueled. It turned out that the voltage regulator behind the counter unit had broken. That was not a difficult repair and I still had a used regulator from a scrap car.
Text and photo Jacques van den Bergh