The difference between gauges and warning lights

"There was a time when automotive enthusiasts wanted their vehicles to have gauges not idiot lights."

There was a time when automotive enthusiasts wanted their vehicles to have gauges not idiot lights. What is an idiot light you say? An idiot light is a warning light, that usually is in the instrument cluster, that comes on when there is a problem. A red light indicates a serious problem and the best course of action is to stop driving whereas an orange or yellow light is a cautionary warning that something is wrong with a system but probably not serious enough that you cannot proceed.

Gauges were preferred because, like the manual transmission, the driver felt more in control of his destiny. The engine temperature, oil pressure, and fuel level gauges as well as a tachometer were the gauge package option of choice.

A real gauge had numbers on it with meaning. Most vehicles to this day have engine temperature gauges. A lot of them have forgone the numbers and only have a C for cold on one side and an H for hot on the other. Somewhere in the middle is where the needle ends up pointing when the engine is up to operating temperature.

If your vehicle is more “enthusiast” oriented it will have temperature values. Most fully warmed up vehicles will reach a temperature between 80 and 100 degrees Celsius. If you are a driver that watches your gauges you will expect that when functioning correctly your temperature gauge will hover around the 90. Climb a hill in the heat of summer and it will creep past the 100 mark. Coast downhill and somewhere just above 80 is what you would expect. When this gauge starts to read too low it was time for a new thermostat. When the gauge was reading too high there was bigger trouble, maybe the radiator, maybe the thermostat was stuck closed.

The temperature gauge allows the driver to react to excursions. If the temperature is creeping up on the high side the driver might decide to reduce the heat load on the engine ( gear down and slow down) or maybe turn off the air conditioning or turn on the heater.

In the case of the warning light (or idiot light) when the vehicle was overheating on would come a red light to tell you the vehicle has overheated; you better do something quick.

The best option likely being to stop. No gauge to watch meant no time to react. No plan of attack.

Most new vehicles have stuck with some level of basic gauges but there is an added twist. Usually there is an extra display to alert you with symbols or words to let the driver know what is going wrong. Some vehicles even have driving tips. “Roll up your windows for better fuel economy” and “Do not idle the vehicle to warm it up” are two that come to mind that I have seen.

If you are a gauge watcher when you drive you may have noticed something strange about the gauges in your new car. They seem to always read the exact same value. Very little excursion.

The manufacturers decided that the gauge watchers are happy when the gauges do not stray. I have noticed that alot of temperature gauges read 90 when the real engine temperature is between 70 and 110 degrees Celsius. I guess they feel this is more comforting for the driver.

When is a gauge no different than a warning light? If you drive a newer vehicle check out your engine oil pressure gauge if you have one. Does it seem like your oil pressure is always rock solid and other than when your engine is off that gauge stays dead centre? That gauge is no different than a warning light. Oil pressure varies a lot. A fully warmed up vehicle will have very little oil pressure at idle. Less than 5 pounds per square inch is common. As the speed of your engine rises the oil pressure should climb to 40 or 50 pounds per square inch.

The new oil pressure gauge is only a switch. As long as the oil pressure is above zero or close to it your gauge will read dead centre. To coin a new term, welcome the idiot gauge.

Trail’s Ron Nutini is a licensed automotive technician and graduate of mechanical engineering from UBC. E-mail:

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