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Hey, Why Is My Radiator Leaking?

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Four common causes for a vehicle Radiator Leaking and their related parts.
The radiator is a component of the engine's cooling system. It is located in the front of the vehicle and uses airflow across the radiator core to transfer the heat developed during engine combustion to the outside air. The system is under pressure to allow the system to operate at higher temperatures to help with complete combustion and minimize vehicle emissions.

Have You Noticed a Leak In Your Vehicle's Radiator?

A radiator leak is commonly caused by a loose/broken radiator cap, damage in the radiator hose, internal chemical electrolysis, or a crack in the tank due to impact or wear. Also, note that a coolant reservoir leak can be commonly mistaken for a radiator leak.

This can result in overheating, engine damage, and unreliable performance. So, it's crucial not to overlook the bad signs and take prompt action. For example, if you notice coolant puddles or a decrease in your vehicle's coolant level, it indicates that the radiator fluid is seeping out. Ignoring these warnings can lead to costly repairs and inconvenience down the road.

Remember, promptly addressing a leaking radiator is an investment in your vehicle's longevity and peace of mind.

Let's Get To The Bottom Of It!

  • Q: Do you see a red, yellow, or green crust around the radiator hose ends?

    The radiator hoses are like flexible tubes made of rubber. They connect to the radiator and the engine block through firm hose adapters. They carry the coolant from the engine to the radiator and back again. Over time, the rubber hoses can become stiff and fragile because they're made of rubber. Additionally, when the coolant becomes acidic, it gradually weakens the hoses from the inside. If you notice a coolant leak, it may be because the hoses start leaking at the connections between the fittings and the hose itself. You might see a dried, crusty material of a specific color, meaning that the coolant has been leaking.

  • Q: Is the engine oil texture resembling a milkshake?

    The head gasket is like a seal that connects the engine's head to its block. Its main job is to keep the coolant passages separate from the oil passages and the combustion chamber. However, the coolant can become acidic if the engine gets too hot or the cooling system wears out. This acidity and electrolysis can damage the head gasket and create leaks. As a result, the coolant can enter the cylinder and pass through the piston rings, eventually ending up in the crankcase where the engine oil is stored; this results in a mix of coolant and oil. When this happens, the engine oil looks milky, resembling a dark milkshake.

  • Q: Are there pinhole leaks in the radiator?

    The coolant must have a certain alkalinity level to stay healthy. However, as time goes by and the coolant gets used, it becomes more acidic. This acidity allows the coolant to conduct electricity. This creates a process called electrolysis, which can damage plastic and aluminum parts in the engine. As a result, these components start to wear out, and small holes, called pinhole leaks, can form.

  • Q: Do you notice coolant puddles under your vehicle?

    The radiator comprises two tanks on each end of the core. Its purpose is to allow coolant to flow from one tank through the core, into the other tank, and back to the engine. The radiator's core is typically made of aluminum or copper, while the tanks are made of plastic. A rubber seal between the core and the tanks is in place to keep them connected. However, as time passes and the radiator is used, this seal can become weak and brittle, eventually cracking. When this happens, it can lead to a leak underneath the vehicle.

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Vehicle Health Inspection Proof

Explore the following typical inspection results that show a potential cause for the symptom and select the one you believe is similar to your vehicle's issue.

The coolant reservoir is leaking and causing the low coolant warning light to appear on the dashboard, resulting in engine overheating

The proof image shows the coolant reservoir leaking at the seam, which explains the low coolant level. Therefore, the coolant reservoir must be replaced with a new one to fix the issue.

When the customer brought in their vehicle, they were concerned about the low coolant light popping on the dashboard every morning. The light would turn off after driving for a while, but now it's consistent. The customer also mentioned they hadn't noticed any coolant puddle on the ground.

During a test drive, the technician confirmed that the low coolant light was on. As part of a vehicle health inspection, the technician discovered that the coolant level was low, and there was evidence of coolant underneath the coolant reservoir.

To further investigate, the technician used a coolant pressure system tester. After filling the coolant correctly, they pressurized the system to 12 psi. Unfortunately, the coolant reservoir was leaking at the seams during this test. This leakage was the cause of the low coolant level, and the reservoir will need to be replaced.

Does the issue look like this? if not accessible your shop will document it
The coolant is overflowing the reservoir because the radiator cap is not holding the specified psi to keep coolant healthy

The proof image shows the radiator cap being tested and failing to hold pressure. This explains why the coolant is boiling over and causing the overflow tank to overflow. The technician will replace the faulty radiator cap with a new one to resolve the issue.

When the customer brought in their vehicle, they were worried because the overflow tank in the cooling system was boiling over, even though the engine didn't seem to overheat. They mentioned that they had been adding coolant every morning to keep up with it.

During a test drive, the technician confirmed the coolant overflowing in the overflow reservoir. However, during the initial vehicle health inspection, the technician found no issues related to the customer's concern.

To investigate further, the technician checked the acidity level of the coolant, and it was within the acceptable range. They then used a cooling system pressure checker to look for leaks but found none.

Next, the technician examined the radiator cap and discovered it held less pressure. The radiator cap is supposed to hold up to 12 pounds per square inch (psi), but it was failing and only holding less than 4 psi. Therefore, the radiator cap needs to be replaced.

Does the issue look like this? if not accessible your shop will document it
The radiator is leaking coolant, causing fluid loss, resulting in engine overheating.

The proof image shows the radiator leaking, explaining why a coolant puddle is under the vehicle. This confirms the need for a radiator replacement to resolve the issue.

When the customer dropped off their vehicle, they mentioned noticing a red liquid puddle where they usually park.

During a test drive, the technician encountered no issues related to the customer's concern. However, during a vehicle health inspection, the technician noticed the coolant level was low.

To investigate further, the technician used a cooling system pressure tester. They connected the tester to the same place where the radiator cap goes and increased the pressure to 12 pounds per square inch (PSI), which is the rating of the radiator cap.

The technician discovered the radiator was leaking between the tank and the core through the test. As a result, the radiator will need to be replaced.

Does the issue look like this? if not accessible your shop will document it
Testing the coolant on a tool. The result showsh that the coolant is acidic and needs to be exchanged

The proof image shows the voltage test, demonstrating the need for coolant replacement. In addition, it helps confirm the presence of electrolysis in the coolant. Finally, it supports the technician's recommendation to replace the corroded radiator and perform a cooling system flush to prevent further issues.

When the customer brought in their vehicle, they mentioned noticing coolant on the ground underneath it. They even saw a tiny leak in the radiator that looked like a small hole, as if someone had poked it with a needle.

During a test drive, the technician detected the smell of coolant after driving for a bit. Upon pulling the vehicle into the service bay, they saw coolant coming out of the radiator through a pinhole.

During a vehicle health inspection, the technician discovered the radiator leaking from a pinhole. They also noticed that the coolant level was low. To investigate further, the technician checked the pH level of the coolant. They found that it was highly imbalanced, going beyond the normal range.

In this case, chemical electrolysis might be causing damage from the inside of the radiator and creating the pinhole. So, the technician conducted a test using a digital voltmeter. They placed the positive probe of the voltmeter in the coolant and connected the other end to the negative battery cable.

The results showed a current of 400 millivolts in the coolant, confirming that electrolysis was the cause of the pinhole leak. Therefore, the radiator needs to be replaced. The mechanic used handy tools in this whole process; this is the type of service you should expect regardless if you're servicing a Japanese or American vehicle.

In addition to replacing the radiator, the technician recommends a cooling system flush. This is necessary due to the imbalanced pH level of the existing coolant. Flushing the system and using fresh coolant will significantly reduce the risk of electrolysis and causing future leaks.

Does the issue look like this? if not accessible your shop will document it
The dipstick shows a very brownish milkshake-like oil. This indicates the head gasket is leaking, allowing coolant to mix with engine oil

The proof image provided shows the milkshake-like appearance of the engine oil, indicating the faulty radiator gasket. This is a significant issue that requires further investigation and action to resolve.

When the customer brought in their vehicle, they mentioned it was difficult to start it. Additionally, they had been checking the engine oil and noticed that it looked like a milkshake in color.

During a test drive, the technician observed a puff of white smoke from the exhaust when starting the vehicle. They also noticed that the engine took longer to crank before starting.

The technician performed a vehicle health inspection and found the coolant level low. But unfortunately, they also discovered that the engine oil had coolant mixed into it, resulting in a chocolate milkshake-like appearance.

The technician used a block tester and special testing fluid to investigate the issue further. They replaced the radiator cap with the block tester and started the vehicle. Almost immediately, the testing fluid changed color from blue to yellow. This confirmed that the head gaskets had failed.

Based on these findings, the technician recommends a more extensive engine tear-down to verify the damage's extent. This will help determine whether the head gaskets and the engine can be repaired or if a complete replacement is necessary.

Does the issue look like this? if not accessible your shop will document it
A coolant leak can build up crustic material around the leaking area, like coolant hoses

The proof image provided shows the crusty build-up of dried coolant, confirming the need to replace the radiator hoses. The crusty material is a clear indication of coolant leakage. By replacing these hoses, the technician will address the issue and prevent further leaks in the cooling system.

When the customer brought in their vehicle, they noticed some pink crusty stuff around one of the hoses while checking the engine oil. They described it as similar to the crusty material that forms around battery cable ends, even though the hose is nowhere near the battery.

During a test drive, the technician didn't notice anything about the customer's concern. However, during a vehicle health inspection, the technician observed that the coolant level was low, and the radiator hose had a crusty build-up around the adapter where the feed hose connects from the de-gas bottle.

To investigate further, the technician used a cooling system pressure tester. They connected it to the de-gas bottle and increased the pressure to the maximum limit recommended by the manufacturer, 12 pounds per square inch (PSI).

Through this test, which is also common for DOT inspections, the technician confirmed that the coolant hose was leaking. As a result, they recommend replacing both the upper and lower radiator hoses, as well as both heater hoses.

Does the issue look like this? if not accessible your shop will document it

Typical Fixes to Address the Cause(s)

The following chapters bases themselves on experiences from our auto repair shop; we'll describe related problems' causes and fixes.

"Coolant Reservoir Replacement" fixes "Leaking coolant reservoir"

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Hey, Why Is My Radiator Leaking?
Sometimes a problem is more challenging to describe than it initially looked like. If you are not sure your problem is described by this article, please find below similar vehicle symptoms, which might describe better the issue you are experiencing.

Other things your auto repair shop might talk about:

Coolant leaking. Internal combustion engine. Losing coolant. leaky radiator valve. water pump.