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What The Low Coolant Light Means

Losing Coolant but No Visible Leak

When you see the low coolant light appear on your dashboard display, the most obvious cause is exactly what you might think, that your coolant is low. You need to know that, even though this is the most obvious cause for the light to come on, it’s not the only cause for the light to come on. In fact, there are a variety of reasons that can lead to low coolant levels in general as well as several reasons for the light itself to malfunction. If you’re concerned with your own low coolant light, we can walk you through all the potential causes and what you may be able to do about it.

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What is the Coolant Light For?


The coolant level light is one of the lights that should normally illuminate very briefly when you first start your engine and then go out again right away when things are all working properly. If it stays illuminated after that then it is warning you that either the coolant levels in your car have fallen below the normal level or that something has malfunctioned in a way that it is keeping it on. Your engine is at risk of overheating when this is on, so even though some drivers may want to let this slide for a while, you don’t want to let it go for very long.


If you’re not sure what the coolant level light looks like, you should check your owner’s manual to be certain. There are actually several different images that are used depending on the make and model of your car. One of the most common looks like an old-style thermometer submerged in liquid. Another looks like a box of liquid with a small chimney, but there are several more designs which can make it confusing to simply describe without knowing which vehicle you're driving. Your manual will confirm for you which it is.


Whatever the reason for the low coolant light to come on, whether it’s a genuine coolant issue or not, it needs to be taken seriously and addressed before things progress into problems that cause more damage and cost you more money to repair.


What Causes the Low Coolant Light to Come On?


When the coolant level light is illuminated you have a handful of possibilities that you’ll want to investigate as potential causes.


  • Low coolant levels: This is the obvious cause of a low coolant level light coming on. It likely indicates you have a leak in your coolant system somewhere unless it has been quite a while since you had your coolant levels topped up.
  • Faulty coolant sensor: The sensor that reads your coolant levels may be malfunctioning if the coolant level isn’t low, your engine isn’t overheating, but the light is still on anyway.
  • Bad wiring: It’s possible your coolant sensor itself is working fine but the wiring that leads to it has become worn or loose and is not ending reliable signals any longer.
  • Broken radiator cap: The coolant sensor relies on pressure in the radiator to maintain an accurate reading. If the radiator cap is broken, then you can’t maintain that pressure in a proper way. The result of that will be inaccurate readings from your sensor which could cause the coolant light to turn on.
  • Broken intake manifold gasket: The intake manifold provides fuel and air to the cylinders in the engine. When the gasket that seals it fails, coolant can leak and cause the low coolant light to go off.
  • Loose or cracked radiator hoses: In much the same way as the radiator cap being broken can throw off your coolant sensor, a faulty hose that is malfunctioning because it is cracked or loose can be throwing off the coolant level and lowering the internal pressure in a way that causes the light to come on when your engine is not actually overheating. Over time all hoses will eventually wear out or crack so it’s worth having these checked if the coolant light is on.
  • Bad head gasket: The head gasket in your engine seals the space between your engine block and the cylinder heads to allow for an air-tight combustion chamber. If the gasket breaks or wears out, coolant can leak into the combustion chamber. Such a leak will trip your coolant sensor and cause the light on your dash to turn on.


What to Do About a Low Coolant Light


As we’ve seen there are a number of potential causes for your low coolant light to go off. How you proceed will of course depend on the exact reason for it.


  • The first and easiest thing for you to do is to perform a visual inspection of your coolant tank. It should have lines on the outside to mark the Max and Min fill points. If you can see that your levels are low, top it up with the appropriate coolant mix specified in your owner’s manual. Not every car uses the same kind of coolant so it's important to make sure you’ve made the right choice. You never want to use pure water unless you absolutely have no other choice, and even then, that should be a last resort to get your car moving long enough to reach a mechanic.
  • When your engine is cool, check your radiator cap and the seal around it. If you find it worn or broken in any way, try replacing the cap with a new one.
  • Park your car over a clean, dry surface. Whether or not you top up the coolant levels, this will allow you to help diagnose any potential coolant leaks you have. Start the car’s engine and let it warm up to a normal operating temperature. Then turn the car off and let it sit overnight. After a night of rest, move the car and inspect the ground beneath where it had been parked for any puddles or drips.
  • If there is evidence of coolant on the ground, check your radiator hoses and clamps for coolant leaks. If there are any, you can replace the hoses and see if that prevents leaks and turns the low coolant light off. Make sure that, if you do see anything, it is in fact coolant. Condensation from air conditioning and other systems may also drip below your car but that is not a cause for concern.
  • Check around the radiator for dampness, obvious leaks, or a white, crusty substance. This is evidence of a coolant leak 
  • If you’re still leaking coolant but your hoses and hose clamps are working well then you have an additional issue such as a blown gasket head, bad intake manifold gasket, or one of the other issues we detailed. If that is the case, then the problem would be much better addressed by a mechanic. 


If you’re not sure what the problem is and some basic maintenance and observation are not able to help you discern why the low coolant light has come on and how to fix it, you’re going to want to head to a mechanic as soon as you can. Issues like a blown head gasket are extremely damaging to your vehicle and could completely destroy your engine if not addressed as quickly as possible.

Can I Drive With a Low Coolant Light On?


While it’s possible you can drive for a short time, and potentially a substantial period of time with the low coolant warning light illuminated on your dash, it’s in your best interests not to do so. As soon as possible you’ll want to get to a mechanic and have the problem diagnosed and fixed as soon as you can.


While a small coolant leak may not be a big problem at first, anything that causes your engine to overheat puts your vehicle at risk. The repair bills associated with fixing major problems like a blown gasket head can cost over $2,000. A blown gasket can lead to additional coolant leaks into the engine that will reduce the overall efficiency of your engine and power output. Left long enough this can cause stalling and seizing in the engine.


Driving with low coolant levels can lead to air bubbles forming in the coolant system which in turn throw off your sensors to give inaccurate readings of the overall engine temperature. 


What is the Cost of Repairing a Low Coolant Light?


The many problems that can cause your low coolant light to come on can have a variety of associated repair costs, which is why it’s best to get the problem fixed as soon as possible. Some of them are serious and some are less so, but the longer the problem stays unfixed, the greater potential for something to grow more complex. These costs are estimates and could vary greatly depending on where you live and the make and model of the vehicle you drive.


  • If all you need is a new bottle of coolant, Walmart sells bottles that range from $8 to $30 depending on size and brand.
  • Radiator caps, if yours is worn out or damaged in some way, are relatively inexpensive to replace and can be found under $10 and range up to $20 or so. Make sure you’ve got one that properly fits your make and model, however. Even some generic brands meant to fit certain cars don’t always form a perfect seal, so test to make sure.
  • Replacing a coolant level sensor that is malfunctioning could cost you between $100 and $140.
  • Replacement hoses for your coolant system can cost $90 to $200 on average. If you’re not comfortable replacing them yourself, a mechanic will of course add a labor cost on top of that as well.
  • A more serious repair would be if the intake manifold gasket is the source of your coolant problem. This repair is more time-consuming and more costly than a simple radiator cap swap, for instance. Repair costs can range from as low as $190 all the way up to $550 or more. Though this one is very pricey, it’s also or you do not want to let slide for very long. If you do not repair the intake manifold gasket, you risk additional problems that range from decreased fuel economy to engine misfires to poor acceleration.


The only way to know for sure what the cost of repairing your problem will be if it's not something as simple as a new radiator cap or topping up fluids which you can do yourself is to take the car into the mechanic to have it properly diagnosed and get an estimate. With such a wide range of potential problems it can save you a lot of time and aggravation to just have a professional manage this problem for you if you’re not comfortable rooting around under the hood on your own.


Is it Worth to Repair a Low Coolant Light?


The warning lights on your car play an important role in making sure your vehicle works at optimal and stays safe and cost-effective the whole time. If the coolant light is staying on for legitimate reasons or just malfunctioning, both of these problems are important and merit attention. As we’ve seen, the host of potential problems is wide-reaching and could be catastrophic if ignored. 


If your car is in otherwise good working order this is definitely worth fixing right away. If you drive an older vehicle that has a host of other problems that are costing you time and aggravation then you need to weigh the whole issue once you are aware of what is happening. If you have a blown head gasket, for instance, and your car is of a substantial age and has other repairs that need to be made, it may no longer be worth your time and effort to put the money into such an expensive repair.


When repair bills top the $2000 mark, you really need to go to a site like Edmunds or Kelley Blue Book and check out the value of your year, make, and model of car. It’s possible that the repair cost could be even more than the value of the car. At that point you need to decide if you value the car enough to bother or if it would be better to sell it for parts or as a junker.




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