Low coolant light: Is it dangerous? And what should I do?

(Last Updated On: March 13, 2024)

Ever experienced your car’s coolant warning light abruptly illuminating while you’re driving? Curious about whether this could pose a threat to your vehicle?

The reason is not far fetched. This may be due to the low coolant level or faulty sensor in the system. Even though this may probably not get you killed, it can cause severe damage to your engine. So, what should you do?

This article will provide you with helpful and extensive information about a coolant warning light. Read on to find out!

What does the coolant warning light mean?

When you start your car’s engine, the warning light will illuminate on the dashboard for about two seconds and then go out. The way the light shows depends on the vehicle you are using. It can either be a box often with wavy lines under it to indicate liquid, a thermometer, or a message “low coolant.” 

Different symbols of low coolant warning light
Coolant warning light has many different styles and colors

Any of these indicators often appears on the driver digital instrument cluster display. If the light does not go out after your engine startup, it means either there is a problem with the sensor system, the coolant is too low, or the temperature is high.  

How does it work?

When your car’s radiator has low coolant, a coolant level sensor uses a movable float device that contains a ring magnet and a reed switch to sense the condition. The reed switch is closed by the ring magnet when you have enough coolant in the radiator but opens when the coolant drops to a certain level. Once the sensor detects the low coolant, a warning light will illuminate on the dashboard to alert you. The coolant level sensor is usually located at the expansion tank’s bottom or on the radiator, depending on your car.

Causes and how to fix the coolant warning light

There are 2 main reasons that lead the low coolant light to come on: Low coolant level and faulty coolant sensor.

what causes the coolant warning light to come on and how to fix
Figure out the causes of the low coolant light to know of what you can fix by yourself or what you have to ask your mechanic for help

Low coolant

When your coolant warning light suddenly comes on, the first reason that appears in your mind is the low coolant level. Yes, you are right! There are many causes that make the coolant level below the standard indicator. Let’s see them!

Unchecked frequently

If your vehicle has a floating sensor in its coolant tank and the coolant level goes below the standard amount, the sensor can trigger the warning light and make it illuminate. The first reason for this issue is that you did not check your engine regularly. Check with your car owner’s manual to know when to change coolant in your radiator.

How to fix

Topping up more coolant to the reservoir is a simple way you can do at your home to fix this issue. Ensure it reaches the full level when the engine is cold. 

Consider flushing your car’s cooling system if you forgot to do this process for time. These steps are very easy to do even if you are a newbie in the mechanical world. 

Other warning signs for low coolant level

  • The odd sweet smell coming from your car after you shut the engine off

    Antifreeze or coolants contains a sweet, viscous liquid called Ethylene glycol. So, you may notice a sweet smell under the hood or in your A/C if there is a leakage that can result in a low coolant level.
  • The air conditioner is not working properly

    The flow of hot air into the cabin is regulated by the coolant. So, if your AC is running and the coolant is low, hot air may start coming from your vehicle’s air-conditioner vents.
  • When the high-temperature gauge is red

    There is a high-temperature gauge on the dashboard to tell you of your engine’s temperature condition. The indicator has an H symbol at the top and a C symbol below. Most often, the temperature level should be at the center. But in a case where the gauge is reading close to H, it means your engine is running hot, and your coolant level is low. 

Coolant leak

A leak can be the primary concern if topping up the reservoir’s coolant level does not fix the low coolant light issue. This can be caused by many reasons like a hole in the radiator, broken hoses, damaged radiator cap, blown head gasket, failed water pump, and faulty expansion tank. You can check for coolant leaks in your car by:

  • Looking under your vehicle in the morning to check if any liquid is on the ground 
  • Feeling the radiator’s underside. Rust-colored stains or whitish deposit often indicate old leaks that have dried
  • Checking the hoses for cracks or any other damage
How to fix

Once you have found the external or internal leak, you can fix it by utilizing your repair service manual’s instructions. For minor leaks, you can quickly repair them at your garage by using a radiator stop leak. However, you may need assistance from your mechanic for major ones if you want to replace some components or parts in the system.

Some of the tools you will need are:

  • Wrenches
  • Bucket or receptacle to collect old coolant
  • Metal shears
  • Radiator hoses
  • Hose clamps
  • New thermostat
  • Painter’s tape
  • New radiato
  • New coolant

Note that the tools you need depend on the part of the car that is leaking. 

Cracked or loose radiator hoses are

When your car engine is running, the radiator hoses are exposed to hot coolant regularly, and this can cause them to break-down over time. They can burst, crack, or loosen causing coolant to escape and prompting the low coolant warning light to show on the dashboard. Seeing a liquid on the ground in the morning, overheating engine, and more can be a sign that one or two of the hoses are bad. You can check the radiator hoses for cracks by:

  • Squeezing the hoses and paying attention to where they bend. If the hose feels very soft, spongy, or hard, it is in poor condition. 
  • Visually inspecting and physically feeling the hoses for cracks.  
How to fix

You can fix the issue by checking the clamps that connect the hoses to the engine and the radiator. If you see any of the clamps loosened, tighten them with a screwdriver. You can do this yourself without going to the mechanic workshop.

However, if tightening the clamps does not solve the issue, you will have to replace the damaged radiator hoses. This can be done without a mechanic’s help if you are an individual who loves doing things yourself. Tool required to get the replacement done.

  • New hoses
  • Safety glasses
  • Pliers
  • New clamps
  • A damp clean rag or degreaser
  • A screwdriver

Faulty radiator cap

The pressure inside the radiator determines how the sensor works. If the radiator cap is damaged or broken, the pressure won’t indicate properly, triggering the low coolant warning light. You can know if your radiator cap is damaged when the lid is stuck, pressure builds up inside the radiator, and the hose breaks, causing the coolant to leak.

Other signs are when the reservoir overflows, the radiator hose is burnt, and your engine starts to billow steam.

How to fix

You can repair the faulty radiator cap by replacing it with a new one when the engine cools completely. Ensure you get a replacement cap that has the same pressure rating as the old cap.

You don’t need a mechanic’s help as you can replace the faulty radiator cap yourself within a few seconds. All you need to do is buy a new cap, place it on the radiator, push it, and twist in a clockwise direction to sufficiently tighten it. 

Bad intake manifold gasket

You will find the intake manifold at the side or top of the engine. Its work is to supply fuel and water into the cylinder, burn them, and provide power. There is a gasket where the intake manifold joins with the engine. If the seal fails, the coolant can leak from there, causing the low coolant light to come on. 

Signs that your intake manifold gasket are: Bad is engine overheating, coolant leak, bad fuel economy, engine stalling, and decrease in power and acceleration.

How to fix

If you want to repair or replace the intake manifold, you will need a new intake manifold gasket, coolant, funnel, gloves, socket and ratchet set, gasket maker or sealer, jack stands, drain pan, and repair manual. This project needs some know-how. It can take about two hours to complete for those who are experienced. Yet, it will be best to take it to the mechanic if you are a beginner. 

  • Bad head gasket 

The head gasket provides a seal between the engine cylinder and block. It also ensures that the coolant and oil flow smoothly. When the head gasket is not working correctly, the coolant can be burned in your combustion chamber. The coolant leaking and burning can trip the sensor causing the warning light to illuminate. You can tell if a head gasket is bad if:

  • Coolant leaks externally from below the exhaust manifold
  • Coolant overflow tank or bubbles in the radiator
  • Exhaust pipe produces white smoke
  • Engine overheats
  • You find coolant on top of a spark plug
  • The oil is milky
How to fix

The solution to this issue is to use a gasket sealer. In case the leak is too big to use the sealant, you need to replace the gasket. For simple repairing as using a gasket sealant, it is very easy to do yourself at home. However, replacing a faulty head gasket can be tricky as it involves removing almost half of the car’s engine. 

The steps include removing the battery cables, draining the coolant, disconnecting the electrical components, removing the intake and exhaust manifolds, removing the cylinder head, and reassembling. 

The tools you need include:

It is advisable to take your car to a professional mechanic for the replacement if you are not a mechanical savvy.  

Faulty coolant sensor

Bad coolant sensor

In case the coolant level isn’t low, your engine isn’t overheating, but the light is still illuminating anyway, there should be a problem with your coolant sensor. The float of the sensor can be stuck at the reservoir’s bottom. The switch may have malfunctioned. 

Bad wiring

Sometimes, the problem is not at the coolant sensor itself, but the bad wiring leads to the wrong coolant warning light to illuminate. If a wire is loose, worn-out, or shorted out, it can make the light come on without any issue. 

How to fix

The above issues may need to drain the coolant fluid inside the system and diagnose the problem. It is advisable to ask for your mechanic’s help. Let professional service handle this.

Can I drive when the low coolant warning light is on?

It is advisable NOT to drive with the low coolant warning light on even though you can potentially do this for a short time. Driving when the coolant is low can cause your engine to get too hot, and this can result in trouble for your journey, vehicle, and yourself. So, what should you do when the low coolant light is on?

When you are on the road

  • Pullover immediately and turn your engine off to prevent further damage that can result in expensive repair cost
  • Allow the car to cool down by letting it sit for half an hour. Then open the radiator cap, check your coolant level, and add more coolant if it is low. 
  • You can also check for possible leaks. If the leak is significant, consider calling a local shop or breakdown service for assistance. However, you can continue your journey if the leak is minor. 
Warning: Open the radiator cap when the engine is hot will cause the hot coolant to spray out.

Tip: In desperate situations, long journeys, and warm temperatures, you can top up the coolant with distilled water if the coolant level is below standard. This will help take your car to the closest shop or home. Don’t forget to flush and repair your cooling system as soon as possible. 

Many new cars have a detection facility that automatically shuts down the car engine to prevent possible damages. Besides, some modern cars will protect the engine by switching to “limp home” mode automatically. 

Read more: Can You Mix Red And Green Antifreeze?

When you are at home/ after driving

  • Park your car over a dry, clean surface and allow it to cool for 30 minutes to 1 hour.
  • Locate the radiator, its components, and hoses to inspect them for any leak.
  • If you find any issue, confirm if it is something you can fix yourself, or you will need a mechanic’s help.
  • If you can’t find the source of the problem, call a local workshop or professional for help.
  • Overall, ensure you do a proper fixing or repair.

How long can I drive with the low coolant?

Usually, you can drive your car for some time when the coolant level is low and the warning light comes on. However, the coolant level often determines how long you can run your car. Confirm if there is a low coolant or no coolant. Then, if there is coolant, how low is it? 

Low coolant level

You can still drive your car for an hour if the coolant level is low (but it is above the minimum). However, if the coolant is below the minimum, use distilled water to top it. This will allow you to drive your car for an hour and take it to the nearest shop service.    

Without coolant in the radiator

According to an experiment done by a group of mechanics, a car can be driven 54 minutes without coolant before it dies. 

Even if you run your car for a few moments without coolant, it can cause severe damage to your engine. The best bet is to call a local shop or repair service. However, if you are alone and in an emergency situation, there is a “till you get home” solution, which is okay for a short time. You can use distilled water instead of coolant to run the engine around 4 miles at a drive speed under 45mhp.

Remember, this is a temporary solution to get you home or to the nearest local repair shop. 

Note : Check the coolant level of your vehicle frequently and do a general checkup of the engine and other parts before a long journey. If you are not an experienced DIYer or mechanical savvy, consult your car owner’s manual for specific details. 

how long can drive with low coolant level

What happens if I drive with the low coolant level/ no coolant?

If you drive your car when it runs out of coolant, there is not always a good outcome. You can experience:

Automatic engine cut-off

If your car has an automatic cut-off feature, the engine will stop automatically when heating up to prevent any damage from low coolant conditions. You will have to wait until the engine cools down before the engine starts again. 

Damage of engine parts

The engine’s parts running too hot can get damaged if you drive with a low coolant level or no coolant. You can experience:

  • Crank failure
  • Bent or warped connector rod
  • Damaged water pump
  • Faulty cylinder and piston timing
  • Burnt head gadget, and more

Note that driving with no coolant can lead to pricey repair bills and irreparable and permanent damage.   

How much does it cost to fix a low coolant light?

The repair costs to fix a low coolant light problem vary with the causes. Where you live and the model and make of your vehicle also determines the cost of repair. So how much does it cost to fix a low coolant light?

Top up or change coolant

A new coolant bottle can range from $8 to $35, depending on the brand and size.

Fix the sensor

It could cost you between $90 to $150 to replace a malfunctioning coolant level sensor.   

Repair the coolant leak

  • Add sealant/ radiator stop leak:
    You mainly pay for the capacity and size of the container. The radiator stop leak or sealant price varies from $5 to $35 for a bottle around 12 ounces and below. But you will get a larger container and bottle at the price range of $35 and more. 
  • Replace radiator cap
    A replacement or new radiator cap should be around $10 and range up to $20. 
  • Replace hoses
    Replacing your coolant system’s hoses can range from $90 to $200. However, if you want to fix or repair it, you can spend around $35 to $65. Note that the replacement price often depends on your car type and the size of the hoses. 
  • Repair the reservoir
    The price of repairing or replacing the coolant reservoir varies based on the mechanic fee and the kind of car you drive. But averagely, it will cost you around $130 to $230 to replace the reservoir.
  • Fix manifold gasket
    The repair cost of a faulty intake manifold gasket can range from $200 to around $600. 
  • Repair/ change head gasket
    You can spend between $1,000 to $2,000 repairing a damaged head gasket. The high cost is not because the parts are expensive but due to the amount of labor required.    

Final thoughts

When the low coolant light illuminates on your dashboard, it means one or more factors that cause the low coolant light to come on is in play.

If you experience any of these problems, the best thing to do is fix the issue immediately or as soon as possible. If you don’t fix these problems on time, it can pose a danger to you and even result in more complex damages to your vehicle that may be expensive to repair.    


1. Why does my coolant light come on, but it’s full?

If your engine is not overheating and the coolant level is not low, but the coolant light illuminates, the sensor that reads your car’s coolant level may be malfunctioning. 

2. Why is my low coolant light only on when cold?

Temperature affects coolant more than other fluids in your car because it has a high percentage of water. The coolant particles’ contraction rate increases as the external temperature reduce. So, when the temperature is cold, especially during the winter months, coolant contrasts. When this happens the sensor can be triggered even if your vehicle’s coolant level falls a bit below the average. It means the same coolant level that does not make the coolant light illuminate during the summer or hot season can make it come on during the winter months or cold season.

3. Why does my low coolant light come on, but the engine is not overheating?

If the engine is not overheating and the low coolant light comes on, the coolant level may be down. Also, the thermostat or water pump may be damaged, the engine may have overworked, the sensor may be malfunctioning, or the radiator may be damaged or clogged.

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