A blown head gasket is a serious issue that can prevent an older car from starting consistently and cause a range of engine performance problems. The head gasket plays a critical role in sealing the engine’s combustion chamber, allowing the engine to maintain proper compression while preventing coolant or oil from leaking into areas where they don’t belong. When the head gasket fails, it can lead to engine overheating, loss of compression, and, ultimately, difficulty starting the vehicle.
In this article, we will explore how to diagnose a blown head gasket, how it can stop an older car from starting consistently, and how to repair the issue if it turns out to be the problem.
How a Blown Head Gasket Affects Engine Performance
The head gasket sits between the engine block and cylinder head, sealing the combustion chamber and preventing leaks of oil, coolant, and exhaust gases. When the head gasket blows, the seal is compromised, and several issues can arise:
- Loss of Compression: A blown head gasket can cause a loss of compression in one or more cylinders, making it difficult or impossible for the engine to generate enough power to start or run smoothly.
- Coolant Leaks: A damaged head gasket can allow coolant to leak into the combustion chamber or the engine oil, leading to overheating or contaminated oil.
- Engine Overheating: When the head gasket is blown, the engine may overheat due to coolant loss or improper circulation, which can further damage the engine.
- Hard Starting or No Start: If the head gasket has failed, especially in older cars, the engine may crank but fail to start because of poor compression or overheating-related issues.
How to Diagnose a Blown Head Gasket
Diagnosing a blown head gasket requires paying attention to specific symptoms and running a few tests to confirm the issue. Here are the common signs and steps to diagnose a blown head gasket:
1. Overheating Engine
If your engine consistently overheats, even after replacing the thermostat or coolant, it could be a sign of a blown head gasket. Coolant leaking into the combustion chamber causes the engine to overheat.
2. White Smoke from the Exhaust
When the head gasket fails, coolant can enter the combustion chamber and burn along with the air-fuel mixture, producing white smoke from the exhaust. This is a classic sign of a blown head gasket.
3. Coolant and Oil Mixing
Check the oil dipstick for a milky or frothy substance, which indicates coolant has mixed with the engine oil. This is another sign of a blown head gasket, as the gasket is no longer keeping the fluids separate.
4. Loss of Engine Power
A significant drop in engine power, misfiring, or rough running could be the result of a blown head gasket causing a loss of compression in one or more cylinders.
5. Bubbles in the Radiator
If you remove the radiator cap (when the engine is cool) and notice bubbles rising in the coolant, it may indicate that exhaust gases are leaking into the cooling system due to a blown head gasket.
6. Coolant Loss with No Visible Leak
If your car is losing coolant, but there are no visible leaks on the ground, it could be leaking internally into the combustion chamber or oil system through a failed head gasket.
7. Compression Test
A compression test can help determine if the head gasket is blown. If the compression readings are significantly lower in one or more cylinders, it’s a strong indication of a blown head gasket.
- How to perform a compression test:
- Remove the spark plugs.
- Insert a compression gauge into each cylinder and crank the engine.
- Compare the readings. If one or more cylinders show low compression, it suggests a head gasket issue.
8. Cylinder Leak-Down Test
A leak-down test checks whether air is leaking out of the cylinder and can pinpoint the source of the leak. If air escapes into the cooling system, the head gasket is likely the culprit.
- How to perform a leak-down test:
- Pressurize the cylinder with compressed air.
- Listen for air escaping from the radiator, exhaust, or oil filler cap. Escaping air from the radiator cap indicates a blown head gasket.
How to Fix and Repair a Blown Head Gasket
Repairing a blown head gasket is a complex job and often requires professional assistance, especially for older cars with intricate engine designs. However, here is an overview of the repair process:
1. Remove the Engine Head
To access the head gasket, the cylinder head must be removed from the engine block. This requires disconnecting various components, including the intake manifold, exhaust manifold, timing chain/belt, and other engine parts. Care must be taken to avoid damaging the head or block during removal.
- Tip: Label each part and take photos to ensure everything is reassembled correctly.
2. Clean the Surfaces
Once the head is removed, the old gasket must be carefully scraped off both the engine block and the cylinder head. Ensure that the surfaces are thoroughly cleaned, as any leftover gasket material or debris can cause sealing issues when the new gasket is installed.
- Tip: Use a plastic scraper to avoid scratching the surfaces, which could compromise the seal.
3. Check for Warped or Cracked Cylinder Head
Before installing the new gasket, check the cylinder head for warping or cracks. A warped or cracked head can cause the new gasket to fail, even after replacement.
- How to check: Use a straight edge and feeler gauge to check for warping. If the head is warped, it may need to be machined or replaced.
4. Replace the Head Gasket
Once the surfaces are clean and flat, place the new head gasket onto the engine block. Make sure the gasket is aligned properly with the cylinder head and engine block. Head gaskets are typically specific to each engine, so ensure that the right one is used.
- Tip: Follow the manufacturer’s torque specifications when tightening the cylinder head bolts to ensure an even seal.
5. Reassemble the Engine
After installing the new head gasket, reassemble the engine by reconnecting all components, including the intake and exhaust manifolds, timing chain/belt, and any other parts that were removed.
6. Replace Fluids
Since coolant and oil may have mixed during the head gasket failure, it’s essential to replace both fluids. Drain and refill the coolant and oil systems, and check for any leaks after the repair.
7. Test the Repair
Once everything is reassembled, test the car by starting the engine and letting it run for a while. Monitor for any signs of overheating, white smoke, or leaks, and perform a compression test to ensure the new head gasket is functioning properly.
When to Seek Professional Help
While it’s possible for experienced DIY mechanics to replace a head gasket, it’s a challenging and time-consuming job. If you are not confident in your mechanical skills or lack the proper tools, it’s best to seek help from a professional mechanic. Head gasket replacement is often costly but crucial to maintaining engine health.
Conclusion
A blown head gasket is a serious issue that can stop an older car from starting consistently and cause a range of engine problems. By recognizing the signs—such as engine overheating, white exhaust smoke, and coolant/oil mixing—and conducting tests like a compression test or leak-down test, you can diagnose the problem. Repairing a blown head gasket requires removing the cylinder head, replacing the gasket, and reassembling the engine with care. Whether you choose to tackle the repair yourself or seek professional help, addressing the issue promptly will prevent further engine damage and restore your car’s performance.
