3 Common Causes For Coolant Leaks | Autance

The optimum performance of a car engine is dependent on a variety of factors. One of the most important is…

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3 Common Causes For Coolant Leaks | Autance © 3 Common Causes For Coolant Leaks | Autance

The optimum performance of a car engine is dependent on a variety of factors. One of the most important is the efficiency of the car’s cooling system so that the engine will not generate too much heat that it compromises its overall function. The way vehicle cooling systems work allow the engine to maintain its operating temperature within acceptable limits by circulating under pressure a mixture of coolant and water. If this pressurized system is not maintained such as what happens when there are leaks, then the engine can overheat. This can also easily translate into damage and eventually costly repairs.

Understanding a Car’s Coolant System

Before we dive into the three common causes of car coolant leaks, it is always best to start with a review of how the system works.

Internal combustion engines typically produce several thousands of highly controlled explosions every minute by virtue of igniting a fuel-air mixture in each engine cylinder. These controlled explosions generate enough energy to move the crankshaft which drives the whole vehicle. With each controlled explosion, heat is also generated. If this temperature is not controlled within optimal engine operation, it can easily destroy or damage the engine. The purpose of a car’s coolant system is to control these excessively high temperatures.

The car engine’s cooling system is composed of the following:

  • Passageways located within the engine block and heads
  • Thermostat to control the car coolant temperature
  • Water pump to move the coolant throughout the entire system
  • Radiator which cools the coolant as it goes through the system
  • Radiator cap which controls the pressure in the car coolant system
  • Interconnecting hoses

A liquid car coolant is pushed through the different passages located in the engine block and heads, picking up the heat generated by the engine in the process. As the now-heated liquid makes its way outside the engine, it goes to the radiator where it is cooled by air coming from the front of the car. Auxiliary fans can also help cool the hot liquid reaching the radiator. The now-cooled liquid is again pushed through the passages of the engine to collect more heat. At the core of this circulating coolant is the water pump. It is the job of the pump to make sure that the liquid coolant is moved through the system.

3 Causes of Coolant Leaks

Since the car coolant system is effectively a closed network of passages, tubes, and hoses as well as larger components like the engine and the radiator, coolant leaks can occur anywhere in the closed system. These can be categorized into three different causes: external leaks, radiator cap leaks, and internal leaks.

External Leaks

As explained above, coolant liquid moves to the engine to pick up heat and is sent to the radiator for cooling before being sent back to the engine. Any leak in any of these components, save the engine, is considered an external leak.

External car coolant leaks are the easiest to diagnose. You don’t even need fancy gadgets to test for anything. One only needs an eye for detail and the perseverance and patience to look for any sign of leak throughout the entire course of the car coolant system except the engine. This means you will need to perform a methodical inspection of the hoses, the radiator, and the coolant reservoir or tank.

Radiator hoses are the most common culprits of external car coolant leaks. Rubber hoses may degrade over time and have the tendency to crack or become brittle. Even a very small fissure can let out liquid coolant to escape. Connections between hoses and other coolant system components can also be sources of leaks. Loose clamps can let liquid coolant escape. It is important to inspect the radiator hose for swelling, cracks, unusual softness, holes, or even collapsed hose. If you see any of these signs, have the radiator hose replaced immediately.

Damage to the radiator can also lead to external coolant leaks. A leaking radiator may be more difficult to diagnose than a leaky radiator hose, however. More often than not, the radiator will have to be removed and checked for the presence of bubbles when it is submerged in water. The radiator is a closed system of tubes. Liquid should flow seamlessly across the series of tubes. If bubbles appear anywhere on the radiator, this typically signals the presence of a leak.

Radiator Cap Leaks

The water pump may be tasked with moving the liquid coolant through the network of tubes and passageways in the car coolant system, but it is the radiator cap that maintains the optimal pressure needed to move the coolant-water mixture. With loss of pressure, the liquid coolant will not be able to move through the system.

The radiator of any vehicle is considered as a pressurized system. This allows the hot liquid coming from the engine to move through the series of tubes in the radiator, allowing the liquid to cool down as it moves along. If the radiator cap is weak or is leaking, then the pressure inside the radiator is not maintained. This can occur if the radiator cap has been seriously damaged by normal wear and tear or does not fit properly into the lid of the radiator. Leaks can also occur if the wrong radiator cap is used.

There is only one way to make certain that there is leak in the radiator cap. You need to bring your car to a service center so that a pressure test can be performed on the radiator cap. Alternatively, you can check your car owner’s manual and check the correct pressure for the radiator cap as well as the correct type of radiator cap to use.

Internal Leaks

Checking for external and radiator cap leaks is relatively easy. However, if you have performed a thorough assessment and found nothing wrong with the external car coolant system, then you’re most likely dealing with an internal leak.

Internal car coolant leaks do not produce a puddle of coolant right under the vehicle as what you would normally see in an external coolant leak. What you will notice is that you are refilling the liquid coolant reservoir more frequently than you used to. One of the most common causes of an internal car coolant leak is a leaky head gasket, hopefully not a blown one.

Head gaskets are very important components of the engine as they form a seal around the combustion chamber. This is located between the cylinder head and the engine block. This allows the engine to produce the correct compression to make it run more smoothly. Head gaskets also contain exhaust gases to aid in maintaining engine efficiency. There is another function of the head gasket and one that is directly related to the integrity of a car’s coolant system. A head gasket helps prevent engine coolant and oil from ever contaminating the combustion chamber.

The reason why the head gasket can get leaky over time is pretty simple. Inside the combustion chamber are high-pressure and extremely hot combustion gases. Outside the combustion chamber but still within the engine is the liquid coolant which can have cold ambient temperature or normal engine operating temperatures. In other words, one side of the head gasket is exposed to extremely hot gases while the other side is a lot cooler. Over time, the head gasket can degrade and develop leaks.

Diagnosing a leaky head gasket is never easy as its location doesn’t really allow for easy visualization. However, if the head gasket leak is external, you can check if there is coolant that accumulates directly under the exhaust manifold. If there is, make sure that this only occurs when the engine is already running and has completely warmed up. Additionally, make sure that there are no other coolant hoses or passages near the head gasket. If there are, a UV dye may be added to the engine liquid coolant before visually inspecting the head gasket using UV light.

If the head gasket leak is located internally, then you may want to check for other signs. One of them is white smoke from the car’s tailpipe. This mostly occurs because the coolant that leaks into the combustion chamber, burns and evaporates. It has a rather sweet smell because of the nature of antifreeze and the white smoke will persist even if the engine is already warm.

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Another possible sign of an internal head gasket leak is the appearance of bubbles in the coolant reservoir or even the radiator. These are exhaust gases that are pushed through the coolant system. There are gadgets that you can use to check if the bubbles you see in the reservoir or radiator are indeed exhaust gases.

Checking your engine oil cap or your engine oil dipstick for the appearance of milky white oil can also be a sign of an internally leaky head gasket. This occurs because some of the coolant that leaks can reach the engine oil through the piston rings.

Your car’s coolant system is designed to manage the excessive heat generated by your engine so that it will run optimally. Any leak within this closed system can result in substantial damage to the engine.


  1. How to Check Coolant – wikiHow
  2. How to Fix an Antifreeze Leak – howstuffworks
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