Picture this: you’re cruising down the road in your trusty Subaru, enjoying the ride, when suddenly, the engine starts to act up. Maybe it’s overheating, losing power, or you spot some strange smoke. One of the scariest possibilities is a blown head gasket. Don’t worry, though! This guide will show you how to test a Subaru for a blown head gasket, helping you diagnose the issue and get back on the road. You’ll gain a better grasp of the common symptoms, learn about the tools you’ll need, and explore the different testing methods. This information will help you save time and money, making you more confident in your car care knowledge.

Recognizing the Signs of Head Gasket Failure in a Subaru

Before you start testing, it’s key to know what to look for. Recognizing the early signs can help you catch the problem before it causes severe damage. Blown head gaskets can manifest in several ways, often making the engine performance unstable. Being aware of these indicators is the first step in diagnosing a potential issue. Observing your car’s behavior is vital for early detection, which can save you from more extensive and costly repairs later.

Common Symptoms of a Failing Head Gasket

The symptoms of a blown head gasket can vary depending on the severity and location of the failure. Some problems show up gradually, while others become apparent quickly. The more you know about these signs, the better equipped you’ll be to identify a possible head gasket issue. It’s a good idea to pay close attention to your car’s performance and behavior so you can notice any unexpected changes. Here are some of the most common warning signs:

• Overheating Engine: One of the most common signs is the engine constantly running hot, even in ideal conditions. This can happen because the head gasket prevents coolant from properly circulating, leading to insufficient cooling.

This occurs because the head gasket, when compromised, allows combustion gases to enter the cooling system. These gases can push coolant out of the system, causing the engine to overheat.

• White Smoke From the Exhaust: White smoke, particularly thick and persistent, often signals that coolant is burning in the combustion chambers. This happens when the head gasket leaks coolant into these chambers.

The coolant, when mixed with the hot combustion gases, vaporizes and exits through the exhaust. The more severe the leak, the more smoke you’ll see. The color and density of the smoke are critical clues.

• Loss of Coolant: If you find yourself frequently topping off your coolant, even without any visible leaks, your head gasket might be the culprit. Coolant can seep into the engine oil or escape through combustion, leading to depletion.

This slow leak can go unnoticed at first, but it quickly becomes an issue as the coolant level drops. If coolant is mixing with the oil, it can compromise the engine’s lubrication, leading to significant problems.

• Milky Oil Appearance: Check the oil dipstick and the oil filler cap. A milky, creamy substance indicates that coolant is mixing with the engine oil, a clear sign of a head gasket issue. This mixture reduces lubrication effectiveness.

This contamination can lead to rapid engine wear and failure if left unaddressed. It is like mixing water with oil in a food processor – the mixture is unable to function properly.

• Bubbles in the Radiator or Overflow Tank: With the engine running, look for bubbles in the radiator or the coolant overflow tank. These bubbles often mean combustion gases are leaking into the cooling system due to the head gasket failure.

Combustion pressure is significantly higher than coolant pressure. Consequently, if gases leak into the cooling system, they will surface as bubbles.

Diagnosing Head Gasket Issues: A Checklist

When you suspect a head gasket problem, it’s important to do a systematic check. Begin by looking for the symptoms, and then use the following steps to start the diagnostic process. This methodical approach will help you pinpoint the issue more accurately. Using a checklist can help prevent you from skipping essential steps and can improve your ability to identify and fix the problem more efficiently. Start by examining the areas mentioned above for the telltale signs.

• Visual Inspection: Begin by carefully inspecting the engine and the area around it. Look for any visible leaks of coolant or oil. Examine the radiator hoses, the coolant reservoir, and the oil pan.

Visual inspections can often reveal obvious signs of a problem. Look for signs of coolant leaks, such as green or pink residue around the engine. Check for oil leaks as well, paying close attention to where the engine bolts together.

• Check Coolant and Oil: Inspect the coolant reservoir and radiator for any signs of contamination. Drain some oil and examine it for a milky appearance. Perform these simple checks to look for coolant mixing with oil.

The coolant and oil reservoirs offer clear evidence of issues. A cloudy or milky oil suggests a coolant leak. The coolant itself might appear contaminated with oil.

• Examine Exhaust Smoke: Pay close attention to the exhaust smoke. Observe the color and thickness. White smoke often hints at coolant leaking into the combustion chamber.

Analyze the exhaust smoke to see if it is consistent with the standard operating output of your Subaru’s engine. Any unusual smoke patterns are important clues.

• Pressure Test the Cooling System: Use a cooling system pressure tester to check for leaks. This method is a great way to verify the system’s integrity. The pressure test will detect if the head gasket is not correctly sealing.

Pressure testing the cooling system provides concrete evidence of a leak. A drop in pressure means there’s a leak somewhere in the system, potentially from the head gasket.

• Perform a Compression Test: A compression test will evaluate the sealing ability of the cylinders. This can help identify cylinders where the head gasket may be leaking. A compression test is more advanced than a visual inspection, and is often the next step in diagnosis.

Low compression in one or more cylinders indicates a potential issue. This test helps determine if combustion pressure is escaping.

Effective Techniques for Testing a Subaru for a Blown Head Gasket

Several methods exist for confirming a suspected head gasket problem. These tests range from simple checks that you can do at home to more advanced diagnostics requiring specialized equipment. The right test depends on your skill level and available tools. Knowing these techniques will let you approach the diagnosis with confidence. This section walks you through each procedure.

Coolant System Pressure Testing

Coolant system pressure testing is a great way to detect leaks, including those in the head gasket. This process involves adding pressure to the cooling system and seeing if the pressure holds. A pressure drop indicates a leak. This test provides a quick indication of problems with the cooling system.

• Preparation: Allow the engine to cool down completely to prevent injury. Open the hood, remove the radiator cap, and make sure the cooling system is at a suitable level.

Safety is key. Working on a hot engine can be dangerous, so let everything cool down before you start. Make sure you can safely access the radiator cap.

• Attach the Tester: Attach the pressure tester to the radiator or the coolant overflow tank. The tester usually has adapters to fit various types of systems.

Select the correct adapter for your Subaru. Ensure the connection is secure to avoid pressure loss during the test.

• Apply Pressure: Use the hand pump on the pressure tester to pressurize the system to the manufacturer’s recommended pressure, often marked on the radiator cap.

Do not over-pressurize the system. Check your Subaru’s manual for the correct pressure specifications to avoid damage to the system.

• Observe for Leaks: Watch the pressure gauge. If the pressure drops, there is a leak somewhere. Inspect the engine for signs of coolant leaks.

Note any pressure loss. Also, inspect components such as the radiator, hoses, water pump, and head gasket area for drips or sprays.

• Testing Time: A typical test will last a few minutes. Check the pressure gauge during this time and inspect your engine’s components.

Some pressure loss is normal. But if the pressure drops significantly and quickly, there is a problem. The rate of the pressure drop indicates the size of the leak.

The Combustion Leak Tester (Block Test)

A combustion leak tester, often called a block tester, is designed to detect the presence of combustion gases in the coolant. This tool can accurately confirm whether a head gasket has failed and is leaking combustion gases into the cooling system. This is a very targeted test.

• Preparation: The engine should be cold. Remove the radiator cap, and ensure the cooling system has sufficient coolant.

As with other tests, safety comes first. Protect yourself from burns by letting the engine cool.

• Fill the Tester: Fill the combustion leak tester with the test fluid. The fluid will change color if it detects the presence of carbon dioxide (CO2).

Make sure you use the appropriate fluid for your tester, as different types of fluids are available. Check the instructions for the best results.

• Attach the Tester: Attach the tester to the radiator opening, creating a tight seal. This prevents outside air from affecting the results.

Secure the tester on the radiator or coolant overflow tank. Make sure it forms a tight seal so that only gases from the cooling system are tested.

• Perform the Test: Start the engine and let it idle. Watch the tester and squeeze the rubber bulb to draw air and coolant vapors through the test fluid.

Run the engine at idle and watch for any change in the fluid’s color. This may take several minutes, but the process is straightforward.

• Check the Results: If the test fluid changes color (often to yellow or green) within a few minutes, combustion gases are leaking into the coolant, indicating a head gasket failure.

A color change confirms that combustion gases are getting into the cooling system. The speed of the color change gives you an idea of the leak severity.

Compression Testing: The Next Level

A compression test evaluates the cylinder sealing capabilities, helping you find leaks in the head gasket, valves, or piston rings. The test will show if each cylinder can hold compression. Understanding how to perform this test will provide valuable information for the diagnosis. This is an excellent way to see how the cylinders perform individually.

• Preparation: Disconnect the fuel pump relay or fuse to prevent fuel from entering the cylinders. Remove all spark plugs. Label them so you know which cylinder they came from.

Safety again is essential, and this will help prevent fuel issues during testing. Take the time to get ready, ensuring each step is carefully followed.

• Attach the Tester: Screw the compression tester into one spark plug hole at a time. The tester will usually screw in or require an adapter.

Choose the correct adapter to fit the spark plug hole. Make sure the connection is snug, so there are no leaks during the test.

• Crank the Engine: With the throttle fully open, crank the engine for about five seconds or until the gauge stops climbing. Record the compression reading for that cylinder.

This action forces the cylinder to generate maximum compression. Note the reading and move on to the next cylinder.

• Repeat the Test: Repeat the process for each cylinder, recording the compression readings for each one.

This will give you a list of compression levels. Write down these numbers.

• Analyze the Results: Compare the readings. Significant differences between cylinders or readings below the manufacturer’s specifications suggest a problem with the cylinder, which could be related to a head gasket failure.

Significant variances mean a problem. Also, low values indicate problems with the engine’s ability to compress air, such as head gasket failure. Any issues should be investigated.

Interpreting Results and Making Informed Decisions

After performing these tests, you will have data that will help you diagnose the problem. The next part will help you analyze the test results, determine the next steps, and explore the possible solutions for a blown head gasket. The results of your tests will help you make educated decisions about repairing your Subaru. This knowledge will put you in control of the situation, so you’re not caught off guard.

Analyzing Test Results: What the Numbers Mean

Interpreting the test results accurately will help you identify the extent of the damage. Here’s a guide to interpret the data. Each test provides different types of data, and you must review the results to identify the problem accurately. This step will help you figure out what to do.

• Coolant System Pressure Test:
  • Stable Pressure: This indicates a healthy system. No significant leaks were found.

  If the pressure holds steady, the cooling system is likely sealed. This suggests the head gasket is okay.

  • Pressure Drop: This means there’s a leak. Look for coolant leaks and signs of combustion gas intrusion.

  If the pressure drops, there’s a leak somewhere. Inspect the area around the head gasket and other components.

• Combustion Leak Test:
  • No Color Change: Indicates no combustion gases are entering the cooling system. The head gasket is likely still sealed.

  This test offers a quick, definitive answer. No color change suggests the head gasket is working.

  • Color Change: Indicates combustion gases are present in the coolant. A blown head gasket is likely.

  The fluid change gives you clear proof. A head gasket failure is extremely probable.

• Compression Test:
  • Consistent Readings: All cylinders have similar compression readings, within the manufacturer’s range. This suggests the head gasket is likely still functioning.

  When all readings are similar, this indicates all is well within the cylinders. The head gasket is also working.

  • Low Readings in One or More Cylinders: Indicates a potential issue in those cylinders, possibly a blown head gasket.

  This means something is causing a leak. The cylinder could have a head gasket issue.

  • Significant Differences Between Cylinders: A large difference means there is a problem. The head gasket or valves could be the issue.

  The difference between the high and low readings tells the tale. This can be caused by the head gasket.

Deciding on the Next Steps

Once you’ve analyzed the test results, you’ll need to decide what to do next. The approach depends on the results and the severity of the damage. Here are a few paths to explore.

1. Confirm the Diagnosis: If one test suggests a problem, but others are inconclusive, consider repeating the tests or consulting a trusted mechanic for confirmation. Verify your findings to ensure accuracy.

Sometimes, multiple tests are needed. You want to make sure the diagnosis is solid, so you can plan the right actions.

2. Minor Issues: For minor coolant leaks, the problem might be fixed by tightening the hose clamps or replacing a faulty radiator cap. This is an easier fix, and if you are sure that it is the issue, it may be the easiest solution.

Sometimes, the solution is easy. Check the easy parts before attempting anything major.

3. Major Issues: A blown head gasket typically requires professional repair, including removing the cylinder head, replacing the head gasket, and often resurfacing the head. This work usually must be done by a skilled technician.

A blown head gasket usually means a more expensive repair. But remember, the fix is necessary.

Seeking Professional Assistance

While you can do some diagnostics yourself, major repairs involving the head gasket are best left to a professional. A mechanic can properly assess the damage, ensure the repair is done correctly, and provide a warranty. Taking your car to a trusted specialist can provide peace of mind and help ensure the work is done correctly.

Consider the professional assistance options when you are not confident in your skills. A qualified mechanic will have the tools and experience to properly repair your Subaru.

• Choosing a Mechanic: Look for a shop specializing in Subaru repairs or with a strong reputation. Check reviews and ask for recommendations.

Choosing the right mechanic is a key decision. Research mechanics and seek advice from friends.

• Getting a Quote: Request a detailed estimate before authorizing any work. Ensure the quote includes all parts and labor costs.

Find out the entire cost ahead of time. Know what to expect and compare quotes before making your choice.

• Discussing the Repair: Talk with the mechanic about the repair process, any potential problems, and the warranty on the work.

You want to have an open line of communication. Ask about the repair process, including any possible problems.

Frequently Asked Questions

Question: What does a blown head gasket look like?

Answer: A blown head gasket isn’t always visible, as it’s inside the engine. Symptoms like white exhaust smoke, coolant leaks, and milky oil are often what you’ll see.

Question: Can I drive a car with a blown head gasket?

Answer: It’s strongly discouraged. Driving with a blown head gasket can cause severe engine damage. Get it fixed immediately.

Question: How much does it cost to fix a head gasket on a Subaru?

Answer: The cost varies but typically ranges from $1,000 to $3,000, depending on the severity and where you get the repair.

Question: What other problems can a blown head gasket cause?

Answer: It can lead to engine overheating, coolant contamination, and even engine failure if not addressed promptly.

Question: How often do head gaskets go bad on Subarus?

Answer: Head gasket failure is somewhat common in older Subaru models, but it depends on maintenance and engine type. Newer models often have improved designs.

Final Thoughts

Now that you’ve explored the process of how to test a Subaru for a blown head gasket, you’re well-equipped to start the diagnosis process. Remember the importance of recognizing the symptoms and using the correct testing methods. By learning these simple steps, you can save money, reduce stress, and improve your knowledge of your Subaru. Whether you choose to tackle the tests yourself or seek professional help, being able to identify a possible head gasket issue is a valuable skill for any car owner. If you suspect a problem, don’t delay. Early detection and prompt action can prevent costly engine damage. Stay informed and enjoy the road.