Low Coolant Levels May Not Mean There’s a Leak


How can it be that the level of coolant in your car is low but you don’t seem to have a leak? Aren’t low coolant levels an indication of a leak? And what is the big deal about coolant in the first place?

It is possible for levels to drop without a visible leak, or any leak at all. Let’s take a look at the critical role coolant plays in an automobile engine and then determine how low coolant can occur without a leak.

What Is the Purpose of Coolant?

The engine of your car or truck is an inhospitable place for just about anything. Sparks are igniting fuel and air and creating hundreds of explosions every minute inside it. Additionally, mechanical parts are moving at hundreds of miles an hour against each other continuously. It is an incredibly hot ecosystem—roughly 195-220 degrees Fahrenheit under ordinary conditions, and even hotter for short periods of time. To give you a sense of how hot that is: Water boils at 212 degrees.

The metal parts inside the engine are designed to withstand hot conditions, but much higher than 220 degrees for an extended period of time would damage them. To keep them from overheating, the cooling system pumps coolant—a 50/50 mixture of water and antifreeze—through the engine to absorb the heat and cool it down. The coolant is then pumped to the radiator where a fan blows the heat out into the atmosphere, dropping the temperature of the liquid. The coolant in the radiator is then pumped through hoses back towards the engine where it begins the cycle all over again.

When it comes to the two elements of coolant—water and antifreeze—water does the work of absorbing heat from the engine and relinquishing it into the air. Antifreeze keeps the water from boiling while the vehicle is operating and from freezing solid in the winter. Additionally, antifreeze includes additives that fight corrosion in the radiator and in the cooling system’s hoses and water pump. Water alone would boil and freeze; antifreeze alone would not cool the engine very effectively. Together as coolant they make a great team and keep the engine running smoothly for thousands of miles.

This is a simplification of the cooling system process, but it offers a glimpse into how it works. Without the cooling system, the engine would overheat and simply stop functioning.

Why Is the Level Low but There’s No Leak?

Make no mistake, low coolant level is a problem that must be addressed. The cooling system is designed to be a closed system, meaning nothing should enter or exit. With all the parts involved—hoses, radiator, radiator cap, overflow reservoir, water pump, etc.—there are many opportunities for liquid to leak or evaporate out of the system, or for contaminants and other fluids to find their way into the system.

If the amount of coolant in the system is diminishing over time, it means it is exiting the cooling system somehow. Often, the leak is so slow or in such a hidden place that it is not visible. For example, a hairline crack in the radiator cap can allow tiny amounts of hot coolant to escape into the air without any visible clues. The amount becomes noticeable over time, but it is difficult to identify the source of the leak. Anytime your vehicle experiences a loss of coolant and you can’t find a leak, check the radiator cap.

The solutions to this particular situation are easy and inexpensive. Coolant may simply be added periodically to replace what is lost. If the problem remains small, this solution may be satisfactory for a while. Most likely, replacing the radiator cap will become necessary because the cap not only keeps coolant in the radiator, it also maintains the pressure necessary inside it for the fluid to be pumped around the engine. The good news is radiator caps are simple and inexpensive to replace.

The issue may be even simpler if the radiator cap is not secured correctly. If that is the case, simply removing it and screwing it back on can solve the loss of coolant.

Other Reasons Coolant Is Disappearing

Another reason the coolant in your car may be disappearing without any visible trace is because the leaking coolant is coming in contact with the engine block and burning up. This scenario may be a small problem like a crack in a hose or a big problem—more on that in a bit.

Coolant may also leak from the overflow reservoir or the reservoir cap. The most common issue with a coolant reservoir is a miniscule rupture in the plastic that is allowing coolant to escape. If the leak is small, it may not be obvious. Steam or slow drips may be difficult to discover or pinpoint.

The reservoir is particularly prone to this issue because the coolant is always hot when it backs up into the reservoir. Although these leaks are small, refilling is only a temporary fix. Eventually the reservoir must be repaired or replaced.

It is important not to overfill the coolant. When adding the water-antifreeze mixture, pay attention to the overfill line in the radiator. Putting in too much taxes the reservoir and can cause a leak.

Small coolant leaks can often be fixed with a chemical additive formulated specifically to repair them, like BlueDevil Coolant Stop Leak. The fluid bonds to aluminum, alloy, or plastic, and eliminates the further loss of coolant from the system.  To use, simply allow the engine to cool, then start it up and run the heater at full blast. Slowly pour the contents of the bottle into the radiator and secure the radiator cap. Allow the vehicle to idle for 45 minutes to circulate the product. Turn off the engine and allow it to cool for an hour before starting it up again. Leaks should be sealed.

Coolant leaking from the radiator may exit the front of the vehicle along with the heat, blown away by the radiator fan. Small leaks may be soldered but larger ones will require a new radiator. Replacing the radiator can cost $1,000, so finding the leak sooner rather than later can save hundreds.

A Blown Head Gasket Can Cause Coolant Loss

The worst-case scenario leading to coolant loss is a blown head gasket, fractured cylinder head, damaged cylinder bores or other major engine damage. The head gasket separates the engine block from the cylinder head. When it corrodes or cracks, it allows gas, coolant and oil to mix, potentially fouling the combustion process, reducing the lubricating properties of oil and preventing coolant from reducing engine heat. Additionally, as it leaks into the oil, less of it is available for cooling the engine.

The head gasket endures searing heat, immense pressure and the constant battering of the various fluids just mentioned. When the head gasket blows, the engine is in danger of imminent failure.

Fixing a blown head gasket is time-consuming and expensive because much of the engine must be disassembled to access it. A typical head gasket replacement costs $1500-$2000. Fortunately, this is much less common than leaking hoses or a corroded radiator.

If the head gasket is indeed the culprit, it may be possible to avoid that kind of expense with BlueDevil Head Gasket Sealer. It is poured into a cold engine with the engine running and heater turned up. While the engine is idling the sealant reacts to the temperature differential at the leak point, forming a permanent bond that is safe for the entire cooling system.

Don’t Ignore a Coolant Leak

Whether the cause of coolant loss is in the radiator, hoses, reservoir or a damaged engine part, the common denominator is that it must be addressed. Given enough time, coolant loss will lead to other damage to the water pump, radiator, engine and more. When a car’s coolant level gets low, the best course of action is to bring it to a car care professional to find the source of loss and repair it immediately. Doing so will cost a little upfront but save a lot in the long run.

BlueDevil Products can be found at AutoZone, Advance Auto Parts, O’Reilly Auto Parts, NAPA, Parts Authority, Auto Value, Bumper to Bumper and other major auto parts retailers.

BlueDevil Products can be found on Amazon.com or at AutoZone, Advance Auto Parts, O’Reilly Auto Parts, NAPA, and other major auto parts retailers.

26 responses to "Low Coolant Levels May Not Mean There’s a Leak"


  1. Eric on October 9, 2022 at 2:56 pm

    Is there anything to tell you the head gasket is gone.
    How do check if the head gasket is blown

    • BlueDevil Pro on October 10, 2022 at 8:13 am


      The tell-tale signs of a blown head gasket are water/coolant mixing in with the engine oil and/or smoke/steam billowing out out of the exhaust pipe. You would also be experiencing the engine overheating. If you are unsure as to what is going on with your vehicle, it would be best to have it inspected by an ASE certified mechanic.

      Thank you!


    • Big WIlly on September 6, 2023 at 7:25 am

      You need a sniffer test done at a garage to see if there are exhaust gases present in the coolant. Also look out for oil in the water, or water in the oil, overheating or white smoke out the exhaust.

  2. Dave on December 22, 2022 at 3:02 pm

    I have pressure in my cooling system when stone cold… pressure builds and pushes coolant out of reservoir… but because of the pressure the coolant can’t return to the radiator… there is no oil in coolant and no coolant in oil… would I use block sealer or head gasket sealer?

    • BlueDevil Pro on January 3, 2023 at 9:04 am


      Have you noticed any smoke/steam coming out of the exhaust pipe or any water getting into the engine oil? Please contact our technical support line at 888-863-0426 so that we can get a little better explanation of the vehicle’s current condition and be able to make any appropriate recommendations.

      Thank you!


  3. david williams on December 24, 2022 at 9:55 am

    i have an 07 silverado 6.0l . it was half frozen this morning and my tank was low. i added hot water to help thaw , drove to town and it started runnning hot. turned off and she sprang a leak. then while sitting i heard a pop. then had heat inside. there waas water all over the motor. now there is no leak visible anywhere… any clues?

    • BlueDevil Pro on January 3, 2023 at 10:54 am


      What is the current condition of the vehicle? Please contact our technical support line at 888-863-0426 for further assistance.

      Thank you!


    • granny judy on October 4, 2023 at 5:07 pm

      Just a question. If there was water all over the motor, is there any left to show a leak? Have you added water to the system to see if it happens again?

  4. Bradley Cadreact on January 4, 2023 at 9:47 pm

    I have a 2013 Kia Soul. It’s got the 1.6L 4-cylinder engine with approximately 132,000 miles. I noticed the coolant in the plastic tank next to the radiator was dangerously low, so I filled it up. After two days and driving about 280 miles, it’s low again. There are no visible leaks. The engine does not overheat. There is no white smoke except on colder mornings when I cold start the engine, which I’m pretty sure is just water vapor because other cars do the same thing on cold mornings. The engine doesn’t make any whining sound while running. I drove on the highway several times. What could possibly be the issue?

    • BlueDevil Pro on January 5, 2023 at 8:42 am


      Thank you for asking about your Kia Soul. It would be difficult to say what the cause is based on the vehicle not really displaying any adverse symptoms. We’d recommend bringing the vehicle to your local shop to have it diagnosed.

      Thank you!


    • Karissa on January 31, 2023 at 2:00 am

      I have a similar problem . Recently had to add 3 litres coolant … did you find out what’s up with your car ?

      • BlueDevil Pro on January 31, 2023 at 8:13 am


        Feel free to contact our technical support line at 888-863-0426 with any questions.

        Thank you!


      • Trai on May 4, 2023 at 2:26 am

        I have same issue. Can someone plz reply? I also had a hard time heating up car this winter. Maybe stuck thermostat related to that coolant disappearing?

        • BlueDevil Pro on May 4, 2023 at 9:10 am


          If you are unsure as to what the vehicle’s issues are, it would be best to bring the vehicle to a certified ASE mechanic for a proper diagnosis.

          Thank you!


    • Saket Aggarwal on May 11, 2023 at 8:54 pm

      Did you figure out what was wrong? Its the same issue with me.

      • James McMullan on June 17, 2023 at 3:48 pm

        I’ve taken my car into 2 different shops at two different times for this problem. Neither could figure out why it’s low. They said inexplicably done cars just burn coolant. It’s this true? They kept it for 3 days each time running tests and no reason for why it’s dropping

  5. Couetney on February 7, 2023 at 7:46 am

    Hi, wonder if you can help. Have Nissan skyline r33 gtst and the coolant is just disappearing, apart from the overheating it has not other signs of a blown head gasket. It’s not dumping it all in one and there’s nothing coming out of the car that I can visibly see underneath or from pipes that I can feel. Any ideas why it’s disappearing?

    • BlueDevil Pro on February 7, 2023 at 8:47 am


      Thank you for asking about your Nissan Skyline. How quickly are you losing coolant? Have you tried replacing the radiator cap? Please contact our technical support line so that we can get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


  6. Walter on May 27, 2023 at 8:48 pm

    I have a 1995 S10 that was leaking coolant but not on the ground it blew the radiator ran hot had a New radiator installed drove it home from the shop now it won’t run

    • BlueDevil Pro on May 30, 2023 at 10:13 am


      Thank you for asking about your S10. Is the vehicle still leaking coolant after the radiator replacement? Please contact our technical support line at 888-863-0426 so that we can get a little better understanding of the vehicles condition and be able to make any appropriate recommendations.

      Thank you!


  7. Tina cruz on July 26, 2023 at 12:55 am

    I have a 2015 Chevy Trax and my Ac and Heater stopped working and my car overheated…we put water in it and it all started working again. Just got an oil change and most of my coolant was gone….what is the problem? And why did my ac and heater start to work again?

    • BlueDevil Pro on July 26, 2023 at 8:55 am


      Thank you for asking about your Chevy Trax. Based on your description, it sounds as though you are experiencing a water/coolant leak. Low coolant levels would explain a/c and heater core functionality and would also explain why the engine overheated. Have you noticed any other symptoms? Please contact our technical support line at 888-863-0426 so that we can get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


  8. ORSAR DENEN SOLOMON on September 12, 2023 at 6:16 am

    My Benz om602 is vomiting coolant from d reservoir Everytime of starting after changing top gasket, please what’s the cause?

    • BlueDevil Pro on September 12, 2023 at 9:06 am


      Have you tried testing for the presence of combustion/exhaust gases in the cooling system? You can use a block-dye test to confirm.

      Thank you!


  9. Christine on January 20, 2024 at 6:47 pm

    I have a 2012 Ford Focus that I’m constantly adding antifreeze to the reservoir which was recently replaced. I see no sign of leaks no smell. Recently had reservoir hose replaced . I had the car run hot for about a mile before I could safely pull over. Oil just changed & no mention of water in oil or signs of leaking but didn’t ask either. Please advise

    • BlueDevil Pro on January 22, 2024 at 8:54 am


      Thank you for asking about your Ford Focus. Have you noticed any smoke/steam coming out of the tail pipe? How much antifreeze are you having to add? Please contact our technical support line at 888-863-0426 so that we can get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


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