The failure of the cylinder head gasket is often blamed for causing severe engine damage in marine engines. However, if gasket failure a cause of damage or is it merely an indication of other, more serious problems?
Gaskets are designed to seal. They either keep various matter inside of something or keep it out, whether gas, solid, or liquid. In the case of cylinder heads, gaskets deal with three different components, all related to combustion:
If a gasket is properly installed, it should function as designed for a very long time. What are the indicators of gasket failure?
Namely, that the gasket is no longer sealing. The cylinder head gasket not only seals the cylinder from external factors, such as preventing water from getting inside the cylinder, but from between different cylinders on an engine (such as gas from one cylinder leaking into an adjacent cylinder. Obviously, such leakage interferes with the combustion process, and engine damage is the inevitable result.
So, what tells the operator that a gasket may be damaged?
- Poor cold starting
- Loss of power
- All cylinders not firing
- Different colored smoke
- High water temperatures
All of these indicators mean that the cylinder head gasket may be damaged. So, you disassemble the engine and replace the gasket. The problem with this is that the gasket may not have been the cause of the failure, but rather a symptom of a different problem. Gasket failure can be caused by a number of different factors, including:
- Improper torque on the cylinder head bolts
- Rapid acceleration of the engine after cold start
- Roughness on the cylinder wall
- Uneven cylinder top
- Loose cylinder liner
- Compression incorrectly set in the ECU
- Defective thermostat
- Cooling system blockage or leak
- Pump failure
- Exhaust system back pressure caused by either leaks or blockages
How do you know that the gasket itself caused the failure?
- Discoloration of the gasket (The area of discoloration usually shows the location of the leak, due to heat, whether caused by the gasket or something else.)
- Excessive flexibility
- Corrosion along the edges or eyeholes of the gasket
- Rough surfaces on either the gasket or engine block
This last point is critical. Modern gaskets for marine use are designed of materials that are engineered to be resistant to corrosion and degradation. In most cases, if it is the gasket itself that has failed, rather than another part of the engine, it is usually the result of improper installation of the gasket. In particular, improper tightening of bolts and installation on dirty surfaces causes these issues. Why?
Simple. The gasket must seat properly and seal. Tightening bolts too tightly warps the gasket, preventing the seal. Dirt or liquid under the gasket prevents a proper seal. Since combustion produces heat, the problems are magnified as the heat becomes excessive, further speeding up failure of the gasket.
So, what can be done?
- Refer to your manual. Marinediesel always lists the torque for bolt tightening in the manual.
- Use only OEM Genuine Spare Parts. The gaskets we use are designed for the engine and made of materials intended to withstand their designed use.
- Realize that gasket failure may be a symptom, rather than a cause. If something is causing gasket failure and that cause is not corrected, the failures will continue.