6 Most Common Subaru Coolant Leaks

Most modern Subarus have a coolant level sensor that will turn on a warning light in the dashboard if the fluid level gets too low. You might notice coolant spots on the ground where you usually park your vehicle, indicating a failure in your cooling system. You will need to identify the problem and get your Subaru repaired promptly to prevent further damage. The coolant in your vehicle is part of a sealed system, so you will not need to add coolant unless there is a leak. If your Subaru keeps running low on coolant, you have a problem that needs to be fixed. 

The most common causes of coolant leaks in Subaru’s are; having a faulty or loose radiator cap, a damaged radiator, a failing water pump, degraded/damaged coolant hoses, a failed heater core, or failed head gaskets. Some of these repairs can be quick, easy, and inexpensive, while others can be lengthy, difficult, and expensive. Parts like a new radiator cap can be replaced for as little as $25, while a head gasket replacement can run you anywhere from $1,500 to $3,000+.

Read on for more details on identifying these cooling system failures, keeping your Subaru’s cooling system running at its best, and what additional damage could occur if your coolant leak isn’t repaired fast enough.

The most common parts causing your Subaru to leak coolant:

1. Faulty Radiator Cap

The radiator cap should only be removed when a coolant system flush is being performed or in an emergency where you have to top off your coolant to get to the repair shop. Your Subaru’s radiator is sealed using a twist-off spring-loaded cap. Over time the internal spring can wear out. When the spring has failed, the cap can no longer hold the increasing pressure from the coolant as the temperature rises. Older Subaru’s with higher mileage can also have the spring in the cap get stuck with debris built up in the cooling system. It is also possible that the radiator cap was installed incorrectly, leading to a leak as pressure builds up in the system. Putting a new cap on every time you have a cooling system flush performed is recommended. 

 2. Damaged Radiator

Your radiator can fail in many ways. The metal can degrade and begin to split apart from being exposed to the elements for too long. The metal fins on the radiator are very thin and can easily be damaged, causing a leak where road debris has impacted it. Also, failing to perform a cooling system flush every couple of years will cause the internal cooling passages in the radiator to degrade and fail. Using coolant that is not recommended for your Subaru can damage your radiator internally, causing a build-up of debris which can clog your cooling system.

3. Water Pump Failure

When the water pump is failing, coolant will usually leak out the bottom of the vehicle. You will see puddles of coolant on the ground where you park. Generally, most Subaru models only need the water pump replaced every 100,000 miles. 

Your water pump could fail early due to a few issues:

  • If the incorrect coolant is used in the vehicle, it can degrade the pump’s internals, causing premature failure. 
  • If there is another cooling system part that has failed, it will put an excessive amount of stress on the water pump leading to its early demise. 
  • The timing belt can wear out, causing the water pump to fail. Your vehicle’s timing belt drives the water pump, so it is a good idea to replace both simultaneously. 

4. Failed Coolant Hoses

There are multiple types of coolant hoses under your Subaru’s hood that can fail. As a preventative measure, your radiator hoses should be replaced every four to five years or 50,000 to 60,000 miles. These hoses are made out of rubber, and after being exposed to the elements and going through thousands of heat cycles, they will degrade and can fail. The cooling hoses usually become hard and brittle and can split open when the cooling system is under pressure. It is also a good idea to use new coolant hose clamps every time the hoses are replaced. 

5. Leaking Heater Core

The heater core provides warmth in the vehicle cabin when you turn the heat on. Think of it as a smaller version of your Subaru’s main engine radiator. Typically it will be located behind the glove box and can be tricky to diagnose as it’s hard to reach. Regular coolant flushes will help the heater core perform at its best and last longer. When this part fails, it usually leaves coolant spots on the carpet where the passenger’s feet rest.

6. Head Gasket Failure

Suppose you do not notice any coolant puddles where you usually park your Subaru, but your coolant level keeps getting low. In that case, the chances are that it is leaking internally into your engine. When your head gaskets fail, the coolant will leak into your engine’s combustion chambers, where it will be consumed while your car is running. A common symptom of head gasket failure is excessive white smoke coming from your exhaust. Coolant entering into parts of your engine it shouldn’t be is a serious problem and must be addressed immediately. Failing to replace your head gaskets when they start leaking can cause damage to multiple cooling system parts as well as your engine. 

How To Keep Your Cooling System Healthy

These preventative measures can be taken to help the parts of your Subaru’s cooling system last longer. 

  • Have a cooling system flush performed every 3-4 years or 30,000-40,000 miles.
  • Replace your radiator cap when your coolant flush is performed.
  • Replace your radiator hoses every four to five years or 50,000 to 60,000 miles.
  • Replace the radiator hose clamps whenever they are removed.
  • Only use engine coolant that is recommended for your Subaru.

Final Thoughts

If your Subaru is leaking coolant, you will need a quality repair shop to help you fix it. It is best to find a mechanic that specializes in Subaru repairs and maintenance. Subaru’s unique engine design can make it difficult for repair shops that don’t specialize in Subarus to diagnose and repair your vehicle correctly. It is essential to get the coolant leak fixed on your car and not to continue driving with a low coolant level, as it can cause damage to your engine and other cooling system components. 

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