Why Is My Engine Temperature Warning Light On?

To protect against overheating, most modern vehicles have an engine temperature warning light, which alerts you to a problem in your cooling system. The first sign of a cooling system problem often occurs when the engine is already in the process of overheating. In many cases, this can be too late to prevent expensive damage.

How does your engine temperature warning light work?

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

• A temperature gauge that has a red light at the hot 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 "engine overheating" 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 light your car has, all are tied to a sensor that’s linked to the engine computer. This sensor monitors the temperature of the coolant circulating through your engine. The coolant absorbs the heat produced by the combustion in the cylinders, and then releases that heat to the atmosphere as it travels through the radiator. When working properly, the cooling system keeps the engine running at peak efficiency and at its ideal operating temperature.

Upon starting, the engine temperature warning light should come on and then go off in two seconds or less. But if it stays on, or comes on while you’re driving, there’s a problem.

Why does the light come on?

There can be a specific reason why your engine temperature warning light is on, or it may be the result of several factors. Some of the possibilities include:

• Low, leaking or old coolant
• A defective thermostat that is stuck closed
• A bad water pump
• Radiator is clogged with debris
• Radiator hoses have collapsed
• Radiator cap is worn out or defective
• Blocked coolant passages inside the engine
• Cooling fan has failed
• Low oil level
• Blown head gasket
• Bad temperature sensor, producing a false warning

Is it safe to drive with this light on?

Under no circumstances should you keep driving after the engine temperature warning light comes on. Overheating will quickly ruin your engine and put a big dent in your pocketbook.

Turn your heater on full blast, pull off the road as soon as you safely can, and shut off your engine once you’re off the roadway. Don’t open the hood and investigate — you could get badly burned. You’ll likely need to call roadside assistance or a tow truck and have your car taken to a mechanic. The best strategy at this point is to not drive your car anywhere until it has been repaired.

How can you fix or prevent it?

When it comes to dealing with the causes that can make your engine temperature warning light come on, there are two basic categories:

• Repairs that you should let your mechanic handle
• Preventive maintenance that you can take care of

Unless you are an experienced automotive do-it-yourselfer, you probably won’t feel confident about tackling most of the mechanical problems that can trigger the light. You can rely on a mechanic’s expertise in dealing with various cooling system problems and related issues.

But there are several basic items of routine car maintenance that will keep your cooling system working well, at least until until some mechanical component fails or wears out. Here’s a list:

• Check your coolant level regularly, adding fresh coolant as needed. Be sure to use the right coolant type and to mix with water.
• Have your cooling system serviced or flushed as recommended by the manufacturer
• Check your oil and other fluids regularly, topping up and changing them as recommended
• Have your vehicle serviced at the recommended intervals

If you notice that your temperature gauge starts reading higher than normal, have your mechanic check it right away. It could be a sign of an impending problem that can be caught and fixed early.