Why the Coolant Level Warning Light Is On, and What to Do

Stephen Fogel
September 25, 2018

Your car’s cooling system keeps the engine from overheating and getting ruined. The system uses a pump to circulate coolant — a mixture of antifreeze and water — throughout the engine. 

But for the coolant to do its work properly, there must be an adequate amount of it in your vehicle. Your low coolant level warning light is there to keep an eye on this.

What is the low coolant level warning light for?

When you start the engine, the low coolant level light should come on for a second or two and then go out. If it doesn't go out, either the coolant level is too low or there is a problem with the sensor system. `

The light usually shows either a thermometer or a box, often with wavy lines to indicate liquid. It can also say “Low Coolant.” Depending on the vehicle, this message can appear on the driver information center in the middle of your instrument panel.

If the light comes on, it’s cause for serious concern. The consequences of a low coolant level can include overheating and the destruction of your engine.  

» LEARN MORE: Get an estimate for your car repair

Why the low coolant level warning light comes on

Repair shops have extensive experience with cooling system issues, and can resolve any issues you are having. Unless the solution is a simple one, don’t try to fix it yourself.

When the low coolant level warning light comes on, you should stop driving. Pull over to the side as soon as possible and shut off the engine to prevent any additional damage.

Here are some reasons why the low coolant light can appear. 

Your coolant level is low

If the coolant level in your reservoir is very low, below the “Min” or “Low” mark, there’s a decent chance you have a leak somewhere. We’ll get to that in a minute — but there is always the chance that you just need to add more coolant.

Solution: This is potentially an easy fix. Simply top up your coolant to the “Max” or “Full” level when the engine is cold. Use a 50/50 coolant-and-water mix, as specified in your owner’s manual. For the next week, check your coolant level frequently (with a cold engine), to be sure that there is no ongoing leak that requires regular top-ups. 

Your coolant reservoir is leaking

Check the sides and bottom of your coolant reservoir for any holes, cracks or fittings where the coolant may be leaking out.

Solution: A mechanic can replace the coolant reservoir.

Your radiator cap is bad

The radiator cap keeps the coolant inside the system, and at the right pressure. A faulty cap can allow coolant to escape, which can turn on the warning light.

Solution: You or a mechanic can replace the bad cap with a new one. If you attempt this yourself, be sure to wait until the engine has cooled down completely — you could get badly burned. Be sure to get the correct replacement cap, with the right pressure rating.

Your radiator hoses are loose, cracked or worn out

Radiator hoses are exposed to hot, pressurized coolant whenever your engine is running. These hoses will eventually wear out. They may crack or burst, or their clamps may come loose. Coolant can escape and trigger the low coolant level warning light.

Solution: Either you or a mechanic can tackle this. Park your vehicle over a dry surface. Let the car run until it is fully warmed up, then park it overnight. In the morning, check for any coolant leaks on the ground underneath the vehicle. Feel the undersides of your radiator hoses for leaks. See if tightening the hose clamps solves the problem. If not, the worn hoses should be replaced.

You have a more serious cooling system leak

If your radiator cap and hoses are fine, but there are coolant leaks around the engine, or coolant puddles on the ground, you could have a faulty radiator, water pump or thermostat housing.

Solution: Get your vehicle to a mechanic immediately. Have it towed if necessary. These repairs will usually require draining the coolant, replacing the defective component and refilling the coolant.

You have a bad head gasket

Your head gasket provides a seal between the engine block and the cylinder heads. It also allows the flow of both oil and coolant. A failed head gasket can lead to a situation where coolant is being burned in your combustion chambers, so you may not see any leaks. 

This will cause a loss of coolant, eventually triggering the warning light. This situation is also very bad for your catalytic converter and other emissions-related components, which can be ruined by the byproducts of burned coolant.

Solution: This problem is bad news, especially for older, higher-mileage vehicles. It’s a very expensive repair. Figure out what your vehicle will be worth, both with and without a functioning engine. If you have an older vehicle with lots of miles, it may not be worth fixing.

If you choose to have it repaired, your engine will be partially disassembled, the gasket will be replaced, and it will then be reassembled. Other processes may be needed if the engine has overheated. This is definitely a job for your mechanic. 

Some newer vehicles may be covered for this repair under the powertrain warranty. 

You have a bad intake manifold gasket

The intake manifold is located on the top or on the side of the engine. It provides the air and fuel that is sent into the cylinders to be burned and provide power. The intake manifold has its own gasket where it’s joined to the engine. This gasket can fail and leak coolant. 

Solution: A mechanic can replace the defective intake manifold gasket. Compared to a blown head gasket, this is a much simpler and less expensive repair.

You have a bad sensor, wiring or warning light

If the coolant level in your expansion tank is actually fine, but the low coolant level warning light is on, this could be the reason. The float may have leaked or gotten stuck at the bottom of the reservoir, the sensor electrodes could be gunked up, a wire could be loose or shorted out, or a switch may have malfunctioned. 

Solution: Have a mechanic check and repair the problem in the warning light system. This may require draining some coolant, so definitely let a repair shop handle it.  

Get it diagnosed by a professional

Can I drive with the low coolant level warning light on?

The safe answer is no, especially if you don’t know the cause and don’t feel comfortable looking around under the hood. To prevent any major engine damage, call a mechanic and have it towed to the shop.

If you’re familiar and comfortable with cooling system care and maintenance, check that there is coolant in your reservoir, and that your engine shows no signs of overheating. If this is the case, you should be able to drive directly to a repair shop to have any necessary repairs done.

How the low coolant level warning light works

The low coolant level warning light is part of a system that includes a sensor inside your cooling system’s expansion tank. It will have levels marked “Min” and “Max,” or “Low” and “Full,” that indicate the actual coolant level when the vehicle’s engine is cold. Your owner’s manual has the correct information for your vehicle. 

The coolant level sensor can be a float-type device, which activates the warning light when a low coolant level sends it to a low position in the expansion tank. Or it can involve electric sensors with two electrodes that are placed at the bottom of the expansion tank. These maintain an electrical circuit as long as they’re covered with coolant. When the coolant level gets too low, the electrodes are exposed to air, the circuit is broken, and the low coolant level warning light on the dashboard is triggered.


Stephen Fogel

About the Author

Stephen has been an automotive enthusiast since childhood, owning some of his vehicles for as long as 40 years, and has raced open-wheel formula cars. He follows and writes about the global automotive industry, with an eye on the latest vehicle technologies.

2 User Comments

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By , June 19, 2017
Yes this also happened to me. I will put in more coolant and take to a shop, money will be a concern.
By , August 24, 2018
My Low Coolant Level won't go out, and the recovery tank is full of coolant. I replaced the coolant level sensor with a brand new one, but light still won't go out. I then disconnected the wire from the sensor. Light still did not go out. I then took a wire and jumped the connector the wire from the sensor normally plugs into. Light still did not go out. I disconnected battery for 10 minutes, then reconnected battery. Light still won't go out. Anybody have any other ideas??

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