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Engine Temperature Warning Light

To prevent overheating, most modern vehicles have an engine temperature warning system. Contrary to popular belief, more engines are destroyed from overheating than from any other cause—including oil and lubrication problems. This is because vehicle owners are accustomed to having the oil and filter changed on a regular basis, but rarely have the cooling system checked or serviced until there is a problem. Often the first sign of a cooling system problem occurs when the engine is already overheating. In many cases, this is too late to prevent mechanical damage.

There are several types of engine overheating warning systems on vehicles.

  • A temperature gauge that has a red colored section at the highest end of the temperature range
  • A red or yellow light that will come on and even blink when the engine temperature is too high
  • A messaging system that will flash an "engine overheating" message in the driver information center. Sometimes the message alternates between a flashing icon of a radiator or radiator fan and then back to the "engine overheating" message.

Regardless of the type of engine temperature warning system, all are tied to a sending unit or sensor that is linked to the temperature gauge and powertrain computer. Later model vehicles may have more than one type of engine temperature sensor deployed because the manufacturers found that an engine could, in some cases, lose all of its coolant and never trigger any type of overheating warning to the driver of the vehicle. To alleviate this problem, the cylinder head temperature sensor was added to the engine coolant temperature sensor, which serves as a layer of protection and a redundant safety measure to the temperature warning system.

When the vehicle is started cold, the temperature gauge needle will stay in the cold section or even below the lowest section of the temperature gauge. If equipped, the overheat light on the gauge should come on and then go off in 1 to 2 seconds or less. The needle should slowly rise to somewhere in the middle range of the gauge as the engine warms up.

Usually, the needle settles a bit lower or higher than the absolute middle of the gauge. This is normal. However, if the needle is higher than 2/3 or lower than 1/3 of the entire range, there is a problem. If the needle settles higher than 2/3, the engine is running too hot and therefore should be checked. If the needle settles below the 1/3 range, either the gauge is not reading correctly or there is a problem with excessive flow in the cooling system, possibly from a stuck-open thermostat. In either case, the vehicle needs to be inspected and diagnosed by a qualified repair shop.

What to Do: Engine Temperature Warning System

If the engine temperature warning system, either by gauge, light, or message, signals that the engine is overheating, turn the cabin heater to the maximum heat range and set the blower motor to high. Turn off the A/C and any other nonessential systems that are running, including the radio. This is to alleviate as much load from the engine as possible and to circulate the remaining coolant through the maximum amount of heat transfer surfaces, like the radiator and heater core. Following these steps will release as much heat as possible.

Pull the vehicle over to the closest and safest place on the side of the road. DO NOT open the hood for at least 20 to 30 minutes. A severely overheating engine can rupture a radiator hose and/or shoot coolant steam out of the coolant expansion tank or radiator cap and severely burn and even blind a person. While waiting, call a tow truck and have the vehicle towed to a qualified repair shop for a complete cooling system inspection and diagnosis.

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