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Coolant Leak (Antifreeze Leak): Causes and Fix Guide

Here's where you can find out all about coolant leak (antifreeze leak)
In this article, you’ll learn all about coolant leak (antifreeze leak)

Any type of coolant leak (antifreeze leak), no matter how minor, has the ability to wreak havoc on your engine. The potential for leaking antifreeze within the cooling system has become a primary focus for late-model alloy engine operational safeguards; any serious fluctuation can result in a flurry of P codes and a noticeable reduction in performance.

What Is A Coolant Leak (Antifreeze Leak)?

Serious damage in the engine can be caused by a coolant leak
A coolant leak can cause irreparable engine damage

To avoid confusion, it should be stated that an engine coolant leak, a radiator coolant leak, and an antifreeze leak are the same things. An engine coolant leak represents a serious failure within the engine’s cooling system. A vehicle’s cooling system is made up of several components, each with a distinct, individual purpose. These components are interconnected by hoses and tubing. The anti-freeze/coolant fluid passing through these components must be kept under pressure to avoid boiling, which will cause the engine to overheat.

A system leak can reduce system pressure or even depressurize the system entirely, causing the anti-freeze/coolant to boil and literally evaporate. That is in addition to the amount of coolant/antifreeze that is lost through the leak itself. If there is not enough liquid coolant within the system, engine heat cannot be dissipated. As a result, irreparable engine damage is likely if the leak is not addressed immediately.

Common Causes Of Coolant Leaks

For every chain, there is a weak link. But first, consider what the chain itself is made of: cooling system components are typically made of brass, steel, aluminum and a variety of synthetic polymers. Some of these materials are very prone to corrosion if not maintained properly. Corrosion is one of the most common causes of coolant leaks throughout the system. This condition can lead to blockages, gasket failure, and component malfunction. This is primarily caused by a lack of scheduled replacement of the coolant or by using the wrong type of coolant. Late-model vehicles typically utilize OAT (Organic Acid Technology) or HOAT (Hybrid Organic Acid Technology) coolant. There is a variety of these types of coolants, designed and colorized for specific makes of vehicles. Choosing the wrong one to put in a vehicle may lead to disastrous results.

The weakest links in the cooling system chain are the radiator and heater hoses. Although hose technology has improved, no hose should be considered a “lifetime” component. High mileage and/or severe-duty environments can lead to hose leakage and loss of coolant.

In addition, the radiator requires a regular visual check; they are positioned in the front of the vehicle and therefore are subject to the damaging effects of road debris, particularly in off-road situations. The fins of the radiator are fragile by design and can leak coolant as the result of a well-placed foreign material impact such as that from a small rock or tree branch. Any coolant leak from the radiator should be addressed immediately.

The heart of the engine’s cooling system is the water pump. Normally positioned at the front of the engine, the water pump’s job is exactly that – to ensure a steady flow of coolant throughout the system. Flowing coolant can absorb and remove heat much more efficiently than static coolant. Typically driven by a timing chain or drive belt, the water pump is a severe-duty component. Failed water pump gaskets or worn bearings commonly result in coolant leaking, particularly if the corrosion has infiltrated the system.

Coolant Leak Locations & Solutions

Once the fact that there is an actual antifreeze leak has been recognized, immediate action must be taken to identify the origin of the leak. Additional mileage may mean the system will cease to function to the point that certain alloys within the cylinder head will distort, warping the head and ruining the seal. Ignoring the issue even further can lead to cylinder head cracking and engine block damage.

Even if a source of the coolant leak can be readily identified, a cooling system pressure test must be performed on the system. Using a professional pump and radiator cap adapter kit, this test applies a duplicate pressure upon the system as if the vehicle were at operating temperature, usually around 16-18 PSI. This test will confirm any earlier observations and reveal any additional leaks.

If no leaks are immediately found, a degree of patience is warranted; some leaks require a constant pressure over a period of time to manifest themselves. Another consideration is to employ a KGP (“known good part”) radiator cap of the correct pressure setting to ensure the cap is not the issue since the cap must be removed in order to perform a pressure test.

Check the cap and the obvious components first: cracked or swollen hoses, damaged radiator fins, and cracked radiator tanks are common locations for leaking antifreeze.

If the water pump begins to exhibit an antifreeze leak, it should always be replaced with a fresh gasket. In addition, the pump’s ability to perform will decrease drastically as the coolant leak becomes more serious. Remember, any leak anywhere in the system results in a loss of pressure.

Since coolant flows through the cylinder head and engine, the head gasket and intake manifold gasket should be thoroughly examined for any tell-tale signs of leakage. It’s not unusual to find a faded trail of coolant leakage from the gasket area; this is proof of a small, periodic but steady leak and should never be disregarded.

If the smell of coolant permeates the inside of the vehicle or if coolant is found puddling on the front passenger floorboard, a leaking heater core is likely the cause. The heater core is the only major cooling system component that is located inside the vehicle, generally positioned underneath the passenger side dashboard. Although evidence of this leak usually cannot be seen in the engine compartment, the effect is the same: failure of the cooling system – and potentially the engine — due to leaking antifreeze.

There is not a truly reliable “quick fix” for any coolant leak. A quality repair of the leak most often requires replacement of the component that is leaking, whether it be a radiator, hose, water pump or heater core. It is important to remember the rule of “cause-and-effect”: what actually caused the leak? A split hose? Old coolant? Road debris? In all instances of cooling system component replacement — particularly a corrosion-related replacement — a thorough system flush is in order…with the correct coolant, to restore system integrity and ensure a long-lasting repair.

Can You Drive A Car With A Coolant Leak?

Driving a vehicle with an engine coolant leak is not recommended. Within a few moments, a small pinhole leak can grow to form a much more serious opening. The risk a driver takes by attempting to make it to a service facility will likely result in irreparable engine damage due to loss of substantial amounts of antifreeze and the overheating condition that will undoubtedly accompany it.


The engine’s cooling system is a sealed, vented system that controls your engine’s temperature. It is closely monitored by the OBD II system, which operates the vehicle’s drivetrain differently during warm-up than at operating temperature. Today’s automotive engines are designed to operate efficiently within an exact spectrum of temperatures. Therefore, action must be taken immediately once a fluid leak has been determined to be leaking antifreeze.

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Austin Aleen

As an automotive service professional for over 30 years, Austin Allen has witnessed technology move forward at a lightning pace. Keeping pace while efficiently conveying these changes as an automotive technology instructor has been challenging as well as rewarding. Upon graduating with a degree in Automotive Technology from Texas State Technical College, he began my career as a suspension and alignment technician for a large-volume Toyota dealership.

Web: https://www.obdadvisor.com/Email: [email protected]
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