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How to Check Coolant Levels: A Step-by-Step Guide

How to Check Coolant Levels

Your car is designed to run at some extremely high temperatures but that doesn't mean it can operate without being kept cool. The range of temperatures that your engine will operate under that are considered optimal are fairly precise. In order to maintain these temperature ranges you've got things like motor oil and coolant that runs through the engine to keep the temperature regulated and ensure everything runs smoothly. Unfortunately, no system is perfect, and coolant can't last forever. There will come a point when your coolant levels are going to run low and knowing how to check your coolant levels will help preserve the life of your car and ensure that you don't have to face any costly repairs from an overheated engine.

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 Do you Check Coolant While the Car is Running?


When you want to check something like the transmission fluid levels in your vehicle it's a good idea to have your car running when you do that. However, it's of vital importance that you know you cannot and must not check your coolant levels while the car is running. Nor should you check them just after the car has been running either. You never want to open your radiator to check out coolant levels if your engine is still warm. The coolant is meant to absorb high temperatures from the engine and as such your radiator is going to be under pressure and the fluid inside will be extremely hot. If you were to open the cap when the engine is still hot, you're going to suffer some serious burns as a result. Always check coolant levels in a cold engine. 


How to Check Your Coolant Levels


Checking the level of your coolant in your car is a straightforward process in most vehicles. Your coolant is probably green or orange in colour but there are other formulations out there that can be blue, gold, pink and so on. It's good to know what your vehicle runs on so that if something were to leak you'd be able to identify it.


If you pop the hood of your car and take a look inside, you'll notice a plastic overflow bottle that's connected to your cooling system. It's made of white plastic and it's translucent so you can see the fluid inside of it.  There should also be a brightly coloured cap on top of it, typically bright orange.


There are going to be two markings on the side of this bottle that you can see. These markings indicate the minimum and the maximum fill level. Your coolant level should be in between those two marks. You'll be able to see the shadow of a liquid through the side of the bottle which makes it incredibly easy to check out.  You don't even need to open the bottle itself to check if you can see that the levels are where they need to be. If everything looks optimal then you just spent less than two minutes to determine that your coolant levels are where they should be.


If you need to do a more in-depth check of your fluid however, and again you want to make sure you're doing this with a cold engine, then you can open the cap and take a look inside. You only need to do this if the levels are obviously low or if you want to check the quality of the fluid. It's possible that over time your coolant will have developed some contamination and a buildup of debris inside. If the colour is off, it's rusty brown or clear looking, or if there are things floating in it then you'll know you need to change it with some new fluid.


If you have an older vehicle than you probably don't have a coolant reservoir that you can see. If that's the case, then you're going to need to remove the cap from the radiator to take a look at the coolant. Again, only do this with a cold car. You never want to check your coolant when the engine is warm and you never want to add more to it when it's warm either. If you add cold coolant to a warm engine you risk cracking the engine block because of the shift in temperature extremes. And if you open the radiator on a warm engine then, as we said, you may get a bad burn from steam and fluid escaping.



What Causes Coolant Levels to Run Low? 


A number of things can cause your coolant levels to run low on your vehicle. The most obvious reason is a leak somewhere in your system. Hoses and gaskets can wear out and develop cracks or breaks that cause coolant to flow out. There are a number of components including the radiator, the water pump, thermostat, overflow reservoir and more that your coolant will run through where there is a potential for a leak to occur.  Aside from leaks in all of those places, there are some other causes for drops in your coolant levels.


Blown Head Gasket


The head gasket is a gasket found at the top of your engine block that seals the cylinder heads. If this is damaged because your engine overheated or for some other reason, even just wear and tear from old age, then your fluid levels could start leaking out here as well with no sign that it's leaking from around the radiator or the coolant reservoir. One way to check to see if this is the problem is to check your oil levels. If you check the oil dipstick and there are bubbles in it or the colour is milky, then you probably have a blown head gasket and coolant is leaking into your oil reservoir.


Overflow Reservoir


Your overflow reservoir has a tube in it that allows coolant to escape if your engine gets too hot and your coolant expands enough that it passes the full mark in the reservoir. This will happen if your car is running particularly hot because it's a very hot day for instance and you have things like your air conditioner and other components running. When it cools down again, the level of coolant will be lower than it should be.


 Radiator Cap


If your radiator cap is damaged in some way or malfunctioning, then you're going to have fluid leaks coming out of that part of the system as well. Remember to only check your radiator cap when your engine is cold, you never want to touch this with an engine that's recently been running. 



When Should I Check My Coolant Levels?


Aside from ensuring that you only check your coolant level when your engine is cold, it's good to know how often you should check them out as well. Even if you're not noticing the symptoms of having low coolant, it’s always a good idea to check it out probably twice a year. A good rule of thumb is to check your coolant levels before the coolest and the warmest times of year,  so give your coolant to look at the beginning of winter and at the beginning of summer. Your vehicle manufacturer may have a different schedule however, so it never hurts to check with your owner's manual and find out if they recommend something different.


Often manufacturers will recommend that you replace your coolant every 30,000 miles or so but again, you want to check with your vehicle manufacturer to make sure. It also depends on the kind of coolant that you're using in your vehicle. Not all antifreezes are made the same and orange antifreeze, for instance, is meant to endure a little more than traditional green antifreeze is.


Can I Top Up My Coolant with Water?


You’ve probably seen in movies when somebody's car overheats on the side of the road and maybe they'll dump a bottle of water into the radiator to bring it down to temperature again. While it's true that you could do this, you really only should do it in that kind of emergency situation when you are stuck on the side of the road in the middle of nowhere with an overheating engine. You could use water to fill your coolant tank to the appropriate level in a pinch, and it's best to do so only as a Band-Aid method to get you to the nearest mechanic so you can get some proper coolant added to the tank.


Remember that antifreeze is able to handle very high temperatures while water is going to boil at 100 degrees Celsius. If you have too much water in your radiator it's going to lower the boiling point of the coolant significantly and that could cause damage over time because your engine needs to operate at higher temperatures than water can handle. So, while it's better than nothing if your tank has run dry and you're nowhere near civilization, it's not an everyday kind of thing.


Some coolants are required to be mixed 50/50 with water in your radiator but that's not true of every kind of coolant. Typically, you want to mix antifreeze and water 50/50 however there are already premixed coolants that you can buy, not technically just antifreeze, that don't need to be mixed. That's why you need to be familiar with the product you're buying and read the label before you add it to your radiator just in case. If you have a premixed coolant, then you don't need to add any water at all.


Signs and Symptoms of Low Coolant Levels 


Aside from routine checks of your coolant levels there are some signs that you can be on the lookout for that will let you know that you might be running low on coolant and you'll need to get your levels topped up. If you're experiencing any symptoms, give your coolant level a look to see how things are.


High Temperature Reading


This one is a little obvious, but it's also one of the best signs that you're having a problem with your cooling system. If the temperature gauge on your dashboard is routinely in the red, then that's definitely a problem. The needle should be staying away from the red and usually spend most of its time right in the middle of between hot and cool. If you find it leaning towards the red and actually dipping into the red, then there is a problem with your engine overheating that is going to need to be addressed. An overheating engine can end up costing you thousands of dollars in repairs if you're not careful.


Sweet Smell


Antifreeze has a noticeably sweet odor that you can't mistake when it starts leaking from somewhere in the system. If the leak is bad enough, you'll be able to smell it in the cabin of your vehicle while you're driving.


Bad Fuel Economy


If your engine is running too hot, then you're going to start burning fuel inefficiently. Your engine typically has to keep things at a lower temperature so that it can recycle certain gases back into the engine compartment to be burned again, reducing pollutants and keeping temperatures down. When the temperature gets too hot because your coolant levels are low, you'll start noticing that you're burning fuel inefficiently and you'll be heading to the gas pumps more often.


Coolant Light


Like a check engine light, you have a coolant light on your dashboard as well. This should probably look something like a thermometer with some wavy lines around it. It will usually show up red when it comes on. When this light does appear, it means that your engine is hitting an extreme temperature and you need to turn it off as soon as you can. This typically means you have a leak in your coolant system somewhere and it's become so severe your engine is at risk of failing.


The Bottom Line


Checking your coolant levels is not a very difficult task at all, especially in modern vehicles that have a tank right there that you can take a look at to make sure everything is the way it's supposed to be. Even in an older vehicle, as long as you do it safely it's not too hard to take a look at your coolant and make sure everything is okay.


When it comes time to top up the fluid the only concern you have is making sure you're using the right kind. You absolutely cannot mix different kinds of antifreeze coolant together. If you have green coolant in the tank right now and you put orange in, you may end up creating a jelly-like sludge that causes your engine to overheat very quickly. So keep that in mind, use the right coolant when you need to and if you have a leak make sure you get it into a mechanic as soon as you can to get it taken care of.

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