If you’re driving along and notice your engine’s temperature is rising, then you have an engine cooling issue. More often than not, the problem stems from a lack of coolant. This is often caused by a coolant leak in your car’s cooling system, which you will need to address immediately. Running a car without sufficient coolant can lead to severe and expensive damage to your engine.
How Coolant Works and Why It’s Important
A coolant works by circulating through your engine and extracts heat. The coolant will carry the heat away from various engine components and keep it at its optimal operating temperature. Most cars will operate with their coolant temperature (shown by the temperature gauge in your dashboard) between 180°F to 240°F.
Without coolant, your car won’t be able to cool the engine as nothing will extract the heat. When this happens, you will see your temperature gauge rise above 240°F. At this point, you should pull over and stop driving since there’s not enough coolant extracting the heat from your engine components. If you continue to drive, your engine will overheat and break down the components inside. Over time, this will cause severe and very expensive damage to your engine.
If you want to learn more about how your vehicle’s cooling system works, watch the video below:
Locating a Coolant Leak
If your engine is overheating, then we recommend checking your coolant level first to determine the problem. To do this, locate your car’s coolant reservoir tank, which is a plastic container with a cap on top. Once your car has cooled down, open the reservoir cap and see if the coolant inside the tank reaches the ‘Maximum’ indicator. If it does, then you don’t have a coolant leak. Instead, your problem may lie with either the water pump or the thermostat, but we will discuss this further later.
If the coolant level is low, refill it with a 50-50 mixture of coolant and water. Keep in mind that some coolant comes premixed, so be sure to check it before you refill it. If the coolant comes premixed, then you won’t need to mix it with water.
Once you refill it, try running the car again. Afterward, if you notice the temperature rises again and the coolant level is already low again, then there’s a leak in your cooling system. If this is the case, then you will need to identify where the leak is happening.
This is how you check for a coolant leak:
External Coolant Leak
It should be quite easy to check if your car has an external leak. After driving your car, park and turn off your car. Afterward, wait for 15 minutes and see if there’s a puddle of coolant underneath your car. Coolants are usually green in color, so if you see a puddle of green fluid underneath your car, then you have an external coolant leak. Keep in mind that there are red coolants as well, so be sure to check what coolant your car has been using.
Now that you’ve confirmed that there’s an external leak, now it’s time to identify where the leak is coming from. These are the three things you should check:
Check the Coolant Reservoir Tank
The reservoir is there to store hot coolant when your engine is operational and pressure is high within your cooling system. When the engine is turned off and pressure in the system goes down, the coolant is then transferred back into the radiator. Because of this, the reservoir tank, or sometimes called the expansion tank, experiences a lot of temperature changes. Over time, this may wear down the plastic and create cracks.
Inspect your coolant reservoir tank for cracks that can cause a coolant leak. If you don’t see any cracks on the tank, then check the bleed hose that connects the reservoir tank to the radiator. These rubber hoses may wear down as well over time which can either create a crack or loosen the connection. If you see a crack or if the connection is loose, then it can leak coolant out. In which case you will need to replace them.
Check the Radiator
If the reservoir tank is fine, the next thing you should check is the radiator itself. Over time, the insides of the radiator will corrode and debris can cause damage which ultimately causes a leak. See if any leaks are coming from the radiator. Also, look out for white deposits or rust-colored stains. These stains indicate a leak that has dried out. If you see a leak or stains on your radiator, then you have a radiator leak.
Additionally, check the hoses connected to the radiator. Much like the reservoir hose, they will wear down over time and develop cracks, and won’t seal properly. See if there are any coolant leaking out of these hoses.
Check the Radiator Cap
Finally, the radiator cap may be the culprit of your coolant leak. It’s a small component, but it plays an important role in the cooling system.
Internal Coolant Leak
If you can’t find any fluid leak externally, you may have an internal coolant leak. An internal coolant leak means that there’s a leak inside your engine causing you to lose coolant fluid. This usually happens when there’s a crack in your engine’s head gasket. The head gasket is there to connect your engine block to the cylinder head and acts as a seal between the two so that coolant can run through to cool your engine as it operates.
If you have a crack in your head gasket, the coolant will leak into the engine’s cylinder, causing you to lose coolant over time. Additionally, the engine’s oil and coolant will mix and ruin both fluid’s performance. Coolant in oil will reduce the oil’s lubricity, which will create more friction in the engine as the oil can’t lubricate the engine properly. Over time, this can cause excessive damage to the engine components. Meanwhile, oil in the coolant will reduce the coolant’s ability to disperse heat from your engine. So not only you will lose coolant, but it will also be less efficient in cooling your engine down.
Here’s how to check if you have a head gasket leak (or a blown head gasket as we often hear):
Check the Your Engine’s Oil
A head gasket leak can cause the coolant and oil to mix. You can check your engine’s oil condition by taking a look at the dipstick. Simply take the dipstick out, wipe it clean, and then reinsert it and pull it out again. Then check the oil condition on the dipstick. Good engine oil should be light brown if not clear, and not too thick. If the oil is milky brown or foamy, then it’s a sign that the oil has been mixed with coolant. This means you have a head gasket leak that causes your coolant to mix with the oil.
Look for Oil Specks in Your Coolant
Open your radiator and reservoir tank cap and inspect the coolant inside. Do you see any black specks floating on top of the coolant? If you do, then that means the engine’s oil has mixed with the coolant. Again, this is because there’s a leak in the head gasket that causes the two fluids to mix.
Pay Attention to Your Exhaust Smoke
As mentioned, a head gasket leak or a blown head gasket will cause coolant to leak into the engine’s cylinder. When the coolant enters the cylinders, it will get burned together with the fuel and air mixture. When this happens, it will result in a thick white smoke coming out of your exhaust system.
In small amounts, a clear white smoke is usually a normal thing as it’s just small amounts of water that has built up inside the engine’s cylinder. This usually happens when you do a cold start in the morning. However, if the white smoke persists even after a few minutes of idling, and especially if the smoke is thick, then you probably have a head gasket problem.
If you see any of the symptoms above, you’re likely experiencing an internal coolant leak with your engine.
What to Do If You Can’t Locate a Coolant Leak
If you can’t find an external leak, then it’s likely you have an internal leak. However, sometimes the leak is so minor that you may not see or notice the symptoms we mention above. To verify the problem, we recommend doing a leak-down test to test out the engine’s cylinder compression. Since a blown head gasket can cause compression loss, this test will help to verify the problem. However, keep in mind that compression loss can be caused by several things, including bad piston rings and valves. But this is still a good indication of whether or not you have a blown head gasket.
Afterward, if there is no cylinder compression loss, we recommend doing a cooling system pressure test. This will verify whether there’s a leak or not within the cooling system.
How to Do Leak-Down Test
You will need a leak-down tester to do a leak-down test. This test will force pressurized air into each cylinder via the spark plug port and see if it holds. If some cylinders don’t hold, then you may have a blown head gasket. The video below will help guide you on how to do a leak-down test:
How to Pressure Test a Cooling System
Pressure testing your cooling system is also a good way to tell if you have a head gasket leak. Also, if the engine’s cylinders did fine in the leak-down test, you may have an external leak that you didn’t notice. In any case, this test helps verify the coolant leak issue. Here’s how to do a cooling system pressure test:
- You will first need to acquire a cooling system pressure test kit. They’re around $60 to purchase, or you can borrow or rent one from a local auto shop. Be sure to acquire one with adapters as different vehicles have different types of radiator caps.
- Remove the radiator cap and then attach the test kit. Be sure to use the correct adapter if necessary. Also, some cars may not have a radiator cap, in which case you will need to remove the reservoir tank cap and attach the test kit to that instead.
- Once connected, pump the plunger rapidly to build pressure inside the system. Keep pumping the plunger until the gauge reads 14PSI. Be mindful to not go over 18PSI, as this can cause damage to the system.
- If the gauge can’t hold the pressure, this is an indication there’s a leak in the system. Also, at 14PSI you should see a coolant leaking out (if there are any leaks in the system).
Here’s a guide on how to check your cooling system pressure:
Fixing a Coolant Leak
Once you verify that you have a coolant leak, you will obviously need to fix it. Otherwise, your cooling system won’t work properly and if you continue driving, you will cause excessive and expensive damage to your engine. The procedure and costs of fixing a coolant leak will vary depending on where the leak is coming from.
If you have a radiator leak, you may be able to solve the issue by simply using a radiator leak sealant, which should cost you no more than $20 to purchase. However, if this doesn’t work then you may need to replace your car’s radiator, which can cause anywhere between $300 to $900 depending on your car’s make and model.
If the issue stems from the reservoir tank, then it will cost you around $130 to replace. Add labor costs into the equation and expect to pay around $220 for a new reservoir or expansion tank. Meanwhile, if you need a new radiator hose to solve the issue, then expect to pay around $170 for a new hose, including labor. Keep in mind there’s more than just one hose in your cooling system, so the cost will be higher if you need to replace more than one hose.
Fixing an Internal Leak
If you have an internal leak such as the head gasket leak, this is where things get expensive. If the leak is minor, then you can use a sealant such as the Bar’s Leak HG-1 Seal to seal the crack in your head gasket. This sealant will cost you no more than $20 purchase, but keep in mind they will only work if the crack is minor. Also, they are a temporary seal and you will still need to replace your head gasket in the future.
A head gasket set typically costs between $200 – $500, but due to the complicated and laborious process of replacing the head gasket, your total replacement cost can be anywhere between $1,000 – $2,000. This is because your mechanic will have to dismantle the top part of your engine to replace the head gasket and then reassemble the engine again. This process can take anywhere between two to three days to finish. And although it’s expensive, we don’t recommend you do this on your own to save costs unless you have the proper training, as it’s very easy to damage other engine components while you’re replacing a head gasket.
You can read more about head gasket replacement costs here.
Other Possible Causes Your Car is Overheating
Coolant leak is often the culprit of an overheating car. However, if you’ve made sure that there are no coolant leaks, then it might be other components that are causing your car to overheat. It’s often caused by either one of these two components:
A thermostat in the engine’s cooling system controls the main and bypass valves, which control the flow of fluid into and from your engine. If the thermostat is faulty, then it won’t be able to control these valves properly. As a result, the coolant won’t be able to flow correctly to and from your engine. The cold coolant won’t flow into the engine, and the hot coolant won’t flow into the radiator. As a result, your temperature gauge will rise.
If you have a faulty thermostat, then you will need to replace it. They’re usually around $110 to $150 to purchase. Add in the labor cost and the replacement cost can be as high as $230.
Bad Water Pump
The water pump is responsible for pumping coolant throughout your engine. In most cars, the water pump runs off the serpentine belt. But sometimes, a water pump is independent and electronically operated, and this type of water pump may fail for no apparent reason. I recently had this experience with my 2015 Mercedes-Benz C-Class.
In any case, if your water pump is leaking or is no longer working, you will likely need to replace it. A water pump will typically cost you between $450 – $650 to replace, and the average price for most cars is $550.
Maintaining Your Cooling System to Prevent Coolant Leak
Your car’s radiator will corrode on the insides over time. When the sediment and debris get carried and circulates in the cooling system, that’s when it can cause damage to your cooling system which will often result in a leak.
Most cooling systems will last up to 3 years at the very least. However, with proper maintenance, a car’s cooling system will easily last for up to 10 years before needing any repairs. Here some things you should do to prolong the life of your car’s cooling system:
Tighten the Radiator Cap
The radiator cap should last for more than 10 years and you won’t need to replace it. You will only need to replace it in extreme cases, such as when rust has built up inside the radiator. Just be sure to check your radiator cap regularly and make sure it’s closed and tighten properly. It has to be closed tight since the radiator cap helps to keep the pressure in the cooling system in check.
Flush the Radiator
As mentioned, your radiator will corrode over time and will become dirty. Flushing the radiator can help to reduce debris and dirt inside the radiator, keeping your cooling system clean and working well. As a general rule, you should flush your car’s radiator every 5 years or 30,000 miles. However, you should check with your manual to see the manufacturer’s recommendation.
A radiator flush will usually cost around $150, including the cost of the new coolant you will need to fill into the system.
Replace the Serpentine Belt
The serpentine belt is used to drive multiple devices in your car, such as the power steering pump, the alternator, and in many cars, the water pump. Make sure to replace the belt before it fails to prevent the car from breaking down while you’re driving. Check for cracks and other signs of damage on the belt. Also, a slipping belt will make a squealing noise as you drive along. If you notice a squealing noise from the belt, you will need to readjust the tension on the belt, or maybe even replace it altogether if there are signs of damage.
A serpentine belt can last anywhere between 60,000 – 100,000 miles. So check your serpentine belt regularly if your car has reached this mileage. A serpentine belt will usually cost around $200 to replace.
When your car overheats, the problem often stems from a lack of coolant which is caused by a coolant leak in the cooling system. An external coolant leak should be easy to spot, and you can use a cooling system pressure tester kit to help you identify where the leak is happening. If you can’t find an external leak, then the problem may be an internal leak caused by a cracked or blown head gasket. You can verify this by looking out for symptoms and do a leak-down test.
If there are no coolant leaks, then your overheating problem may be caused by a faulty water pump or a bad thermostat, which you will need to replace.
As with any other components, your car’s cooling system can last a long time with proper maintenance. Be sure to follow our tips on how to maintain your cooling system and your car should remain healthy over its lifetime.
These tools have been tried and tested by our team, they are ideal for fixing your car at home.