If your Subaru has been running hot, losing coolant, or showing strange white smoke, you might be worried about a blown head gasket. It’s a common issue in many Subaru models, especially older ones.
To test your Subaru for a blown head gasket, check for coolant or oil leaks, overheating, or bubbles in the radiator. Perform a compression test on each cylinder or use a combustion leak tester for confirmation.
But don’t panic — this guide will show you how to check for a blown head gasket step by step, even if you’re not a professional mechanic.
Why Subarus Are Known for Head Gasket Problems
The head gasket sits between the engine block and the cylinder head. Its job is to seal the combustion chamber and keep oil and coolant from mixing. Subaru engines, especially the boxer-style engines like the EJ25, are designed with the cylinders lying flat. This layout helps with balance but also puts extra pressure on the head gaskets over time. As a result, many Subaru owners face head gasket issues once the car reaches higher mileage.
Common models that have had this issue include:
- Subaru Outback
- Subaru Forester
- Subaru Legacy
- Subaru Impreza
Usually, head gasket problems show up after many miles of driving, but early signs can appear sooner if the car overheats or maintenance is skipped.
Common Symptoms of a Blown Head Gasket
Before you start testing, it helps to know the warning signs. If your Subaru has one or more of these symptoms, it’s time to do a proper check.
- White Smoke from the Exhaust. This happens when coolant leaks into the combustion chamber and burns. The smoke often has a sweet smell.
- Milky or Foamy Oil. If you see a milky, coffee-colored residue on the oil cap or dipstick, coolant is mixing with the oil — a clear warning sign.
- Loss of Coolant Without Leaks. When coolant disappears but you don’t see any puddles under the car, it might be leaking internally through the gasket.
- Overheating Engine. A blown head gasket can let combustion gases enter the cooling system, causing bubbles and overheating.
- Bubbling in the Radiator or Overflow Tank. If you see bubbles while the engine runs, that’s air or exhaust gas getting into the coolant.
- Poor Performance or Rough Idle. A bad gasket can reduce compression, causing rough running, weak acceleration, or even misfires.
If you notice two or more of these signs, testing the head gasket is the next smart move.
Tools You’ll Need for Testing
You don’t need a fancy workshop. These simple tools are enough to check your Subaru’s head gasket at home:
- Compression tester
- Leak-down tester
- Coolant gas/block test kit (also called a combustion leak tester)
- Radiator pressure tester
- Flashlight
- Safety gloves
- Clean rags
Safety Tip: Always let the engine cool before opening the radiator or touching engine parts.
Step-by-Step Guide: How to Test a Subaru for a Blown Head Gasket
Now let’s go through the process step by step.
Step 1 – Visual Inspection
Start with a simple visual check.
- Look around the engine for any wet spots or stains near the head gasket area.
- Check for oil leaks or coolant residue.
- Remove the oil cap and inspect the underside. A milky or foamy look means coolant is mixing with oil.
- Look at the coolant in the radiator or reservoir. If it looks brown, oily, or has bubbles, that’s a bad sign.
Step 2 – Compression Test
A compression test checks the pressure inside each cylinder. Uneven pressure can mean the gasket is leaking between cylinders.
How to do it:
- Remove the spark plugs.
- Screw in the compression gauge.
- Disable the fuel system so the engine doesn’t start.
- Crank the engine for a few seconds.
- Note the pressure reading.
- Repeat for all cylinders.
If one or two cylinders show a much lower reading than the others, that’s a clue the head gasket is failing in that area.
Step 3 – Leak-Down Test
This test is even more accurate. It tells you exactly where the air is escaping from a cylinder.
How to do it:
- Bring the piston of one cylinder to the top (TDC).
- Attach the leak-down tester.
- Add compressed air to the cylinder.
- Listen carefully:
- Air from the exhaust pipe means a leaking exhaust valve.
- Air from the intake means a leaking intake valve.
- Air bubbling in the radiator means a blown head gasket.
Repeat for each cylinder. If you hear bubbling in the coolant tank during the test, it’s almost certain the gasket is bad.
Step 4 – Coolant Gas Test (Block Test)
This is one of the easiest and most reliable ways to confirm a head gasket leak.
You’ll need a combustion leak test kit. It’s a plastic tube with a blue liquid that changes color when it detects exhaust gases.
Steps:
- Remove the radiator cap (engine cool).
- Insert the tester in place of the cap.
- Start the engine and let it idle.
- Watch the liquid inside the tester.
- If it changes from blue to yellow, it means exhaust gases are entering the coolant — a clear sign of a blown gasket.
This test usually gives you an answer within minutes.
Step 5 – Cooling System Pressure Test
If the other tests are still unclear, a pressure test can help.
How to do it:
- Attach a radiator pressure tester.
- Pump it up to the pressure shown on your radiator cap (usually around 15 psi).
- Watch the gauge for a few minutes.
- If pressure drops and you don’t see any leaks outside the engine, it means coolant is escaping internally — likely through the head gasket.
What to Do If the Gasket Is Blown
If the tests confirm your Subaru has a blown head gasket, it’s best to stop driving it until it’s repaired. Continuing to drive can damage the engine badly.
Here’s what you should know:
- Repair Cost: Replacing a head gasket is not cheap. It usually costs between $1,200 and $2,500, depending on your Subaru model and local labor rates.
- Parts to Replace During Repair: While fixing the gasket, most mechanics also replace the timing belt, water pump, and thermostat. It saves money in the long run.
- DIY or Professional Repair: If you’re experienced, you can do it at home, but it’s a big job. For most people, it’s safer to take the car to a trusted mechanic.
- Driving with a Blown Gasket: It’s risky. Even short trips can cause the engine to overheat or seize.
How to Prevent Future Head Gasket Problems
A few simple habits can help you avoid this problem again:
- Change the Coolant Regularly. Old or dirty coolant can corrode the gasket and engine parts. Replace it as recommended in your car’s manual.
- Use the Right Coolant. Always use coolant made for Subaru engines. Mixing different types can cause chemical reactions and damage.
- Avoid Overheating. Watch your temperature gauge. If it rises too high, pull over and turn off the engine.
- Check Oil and Coolant Levels Often. Low coolant or oil levels can lead to overheating and pressure changes that damage gaskets.
- Fix Small Leaks Quickly. Even minor coolant or oil leaks can cause big problems if ignored.
Taking care of these small things can save you from a major repair bill later.
Subaru Head Gasket Symptoms
If your Subaru shows white smoke, overheating, or milky oil, the head gasket might be leaking. Watch for coolant loss, bubbles in the radiator, or rough engine running — these are early warning signs of gasket trouble.
Subaru Head Gasket Replacement Cost
Replacing a Subaru head gasket usually costs between $1,200 and $2,500, depending on the model and labor rates. The price can rise if you also replace the water pump, timing belt, or other worn parts.
How To Check Subaru Head Gasket
Start by checking for coolant leaks, white smoke, or milky oil. Then do a compression test on each cylinder or use a combustion leak tester. These steps help confirm if the head gasket is blown.
Blown Head Gasket Subaru Forester
A Subaru Forester with a blown head gasket may overheat, lose coolant, or show white exhaust smoke. You might also notice poor performance and bubbles in the radiator. Fixing it early prevents serious engine damage.
Subaru Head Gasket Issues Years
Older Subaru models, mainly from the late 1990s to early 2010s with the EJ25 engine, often had head gasket problems. Newer models use improved gaskets that last longer and are less likely to fail.
FAQs
How do you test to see if a head gasket is blown?
Check for white smoke, coolant loss, or overheating. Do a compression test or use a combustion leak tester to confirm gasket failure.
Can you drive a Subaru with a blown head gasket?
It’s not safe to drive with a blown head gasket. It can cause overheating and severe engine damage if ignored.
2001 – Diagnosing blown head gaskets?
Look for coolant leaks, overheating, or white exhaust smoke. A compression or leak-down test confirms the blown head gasket issue.
Symptoms of blown head gaskets?
Common symptoms include white smoke, milky oil, overheating, loss of coolant, and bubbles in the radiator while idling.
2014 – FB25 Head Gasket Blown – worth it to repair?
Yes, if your Subaru is in good shape. Repairing the FB25 head gasket can extend your car’s life and performance.
Tips on self-diagnosing the severity of a blown head gasket?
Check for white smoke, oil mixing with coolant, or overheating. The worse these signs are, the more serious the damage.
How do I check for a head gasket leak on a Subaru 2.5L H4?
Do a compression or block test, look for coolant leaks, white smoke, or bubbles in the radiator when running.
How to identify head gasket failure on a Subaru engine?
Watch for overheating, coolant loss, white exhaust smoke, or milky oil. These clear signs often mean the head gasket has failed.
How to tell if a Subaru has a blown head gasket?
Check for white smoke, coolant loss, or overheating. Milky oil or bubbling coolant are strong signs of a blown gasket.
How do you check for a blown head gasket at home? What does a bad head gasket sound like?
Look for white smoke, milky oil, and bubbling coolant. A bad head gasket often causes rough idling or knocking sounds.
Conclusion
Testing your Subaru for a blown head gasket might sound hard, but it’s something you can do with a little time and patience. By checking for white smoke, coolant loss, overheating, or milky oil, you can catch the problem early before it becomes serious. Using simple tools like a compression tester or block tester makes it easy to confirm if the gasket is leaking.
If the gasket is blown, avoid driving and plan for a proper repair to protect your engine. Regular maintenance — such as changing coolant, watching for leaks, and preventing overheating — will help stop future issues. With care and attention, your Subaru can stay reliable and strong for years to come.