Coolant temperature warning light

Pull over now

Get off the road and shut the engine off within the next few seconds. Do not finish the drive, do not "just get it home," do not wait for a place to pull in more comfortably. Coast to the shoulder or a parking lot and turn the key off. An engine that keeps running while this light is on can go from a fixable problem to a ruined engine in a couple of minutes.

What the light means

The car has measured the coolant temperature and it is higher than the engine can safely handle. Coolant is what carries heat away from the engine. When it can't do that job anymore, metal parts start to expand past their tolerances, and gaskets and seals start to fail. This is not a light that means "keep an eye on it." It means stop.

What causes this, most common first

Low coolant is the most frequent cause, usually from a leak somewhere in the system: a hose, the radiator, the water pump, or a gasket. A failed radiator cap can also let coolant escape as pressure builds. Next most common is a bad thermostat that's stuck closed, so coolant isn't circulating even though there's plenty of it. After that, a failing water pump, a clogged radiator, or a broken cooling fan can all stop heat from getting carried away properly. On older or higher-mileage cars, a blown head gasket is also worth ruling out, especially if the coolant is disappearing without an obvious external leak, or if you see white exhaust smoke.

What it takes to fix

Once the car is off and safe, do not open the radiator cap or coolant reservoir cap while the engine is hot. Pressurized hot coolant can cause serious burns. Let it cool first.

The fix depends entirely on what's actually wrong. A low coolant level from a small leak might mean a new hose or a cap, which is quick and inexpensive. A thermostat or water pump is a bigger job but still routine. A head gasket is a much larger repair, and it's the reason this light gets taken seriously rather than shrugged off. The only way to know which one you're dealing with is to have someone look at the cooling system while it's not under load, check for leaks, pressure test it, and check the coolant condition. We do this kind of diagnosis regularly, and we won't guess before we know what's actually failed.

Warning-light symbols and meanings vary by vehicle — always check your owner’s manual. This is general guidance based on what the light indicates, not a physical inspection, and a light on its own never names a failed part.