Diagnosing Gasket Failures

Gaskets have been used on automobiles since their inception. While those early vehicles did not have EGR valve or throttle body gaskets, they did require cylinder head and intake manifold gaskets like modern automobiles.

The gasket provides a seal that prevents the movement of air or liquid from one location to another. For instance, the cylinder head gasket prevents coolant from flowing from the water jacket in the cylinder head into the combustion chamber.

Proper gasket performance is essential to the operation of the entire vehicle (gaskets are even used on taillight assemblies to keep water out of the trunk). So, when a gasket fails, for whatever reason, the effects will usually be noticed by the driver. And, in some cases, severe damage can result. For the purpose of this article, we will concentrate on engine gaskets, in general, and the cylinder head gasket, in particular.

Gaskets are used throughout the engine, providing liquid and airtight seals on the water pump, timing belt (or chain), the valve cover, the intake and exhaust manifolds, the oil pan and the various sensors. Some of these gaskets are external (can be accessed without engine disassembly) and internal (require some engine disassembly). An external gasket can be an oil pan or intake manifold gasket. The major internal gasket is the cylinder head gasket.

Gasket failure can usually be attributed to three causes: (1) the service gasket was installed improperly and never did provide the sealing properties needed, (2) it was damaged during use, or (3) it exceeded its service life (which is not as common today as it once was). Let’s begin our discussion of diagnosing gasket failure with external gaskets.

EXTERNAL ENGINE GASKETS

Starting at the top of the engine, let’s look at the valve, or cylinder head cover gasket. A typical gasket of this type, from a 3.8L V-6 engine, is shown in Figure 1. While age can have an affect on this gasket, the primary cause of failure for this service gasket is improper installation. To avoid oil leaks, always make certain the gasket surfaces are clean and the cover bolts are tightened to the correct torque specifications.

If the gasket surface is not clean, the gasket cannot be seated properly, leading to failure. Some engine designs require a sealing compound, such as RTV, that can overcome this problem to a certain point. Other engine designs use dry gaskets. Always clean the gasket surface on the cover and on the cylinder head. Note: Surface cleaning procedures vary depending on the composition of the mating surfaces. For the correct procedure refer to the appropriate Chrysler service manual.

If the cover bolts are excessively tightened, the cover flange can distort, effectively destroying the gasket seal. These bolts, generally, do not require a lot of torque (maybe, 10 lb.-ft.).

These two problems are also common with the oil pan gasket (Figure 2). The same two causes for failure, and the steps to prevent gasket failure, apply to this gasket, too. Don’t forget to include timing chain cover gaskets in that group (poor surface preparation is more likely to cause failure than over-torquing the retaining bolts).

Long flat-type gaskets, such as those mentioned, could be vulnerable to failure due to improper installation. If properly installed, these gaskets should last the life of the vehicle. Age-related failure is not a concern.

The last external gasket to examine is the intake manifold gasket. When this gasket fails, it can 
result in a vacuum leak which causes driveability issues. And finding a vacuum leak on the modern engines used in today’s cars can be difficult. So, whenever this gasket is replaced, always check the surface for damage and cracks. A straightedge can be used to check for distortion of the mounting surface.

Checking for intake manifold leaks is pretty simple. An intake manifold air leak is characterized by lower than normal manifold vacuum. Also, one or more cylinders might not be functioning properly. Start the engine, but be careful when leaning over the running engine. Next, spray a small stream of water, using a spray bottle, at the suspected leak area. If the engine speed changes, the area of the suspected leak has been found. Replace the gasket, as required.

CYLINDER HEAD GASKETS

The cylinder head gasket, arguably, is the most important gasket in the engine. Not only does it contain the compressed air/fuel mixture in the combustion chamber, it keeps coolant and oil in the respective passages. Typical head gaskets are shown in Figure 3. When a head gasket fails, major problems occur in the engine. And these problems can cause catastrophic component damage, leaving the vehicle owner with a substantial repair bill.

A cylinder head gasket leak can be located between adjacent cylinders, between a cylinder and the adjacent water jacket, or from an oil passage to the exterior of the engine. Possible indications of a cylinder head gasket leak between adjacent cylinders are (1) loss of power, (2) engine misfiring and (3) poor fuel economy. A head gasket that is leaking between adjacent cylinders will result in a 50-70 percent reduction in compression pressure.

Possible indications of a cylinder head gasket leak between a cylinder and an adjacent water jacket are (1) engine overheating, (2) loss of coolant, (3) excessive steam emitting from the tailpipe (4) coolant foaming and (5) coolant in the engine oil.

When a major engine problem occurs, there are several tests that can be performed to determine whether or not the cylinder head gasket is to blame. Let’s review a few of these tests, including the cylinder compression pressure test.

The cylinder compression pressure test can diagnose several engine malfunctions. Before starting this test, be sure that the battery is fully charged and the starter motor is in good operating condition. Also, check the engine oil level and top it off, if necessary. Perform the test in the following manner:
(1) Drive the vehicle until the normal operating temperature is reached
(2) After reaching temperature, remove the spark plugs; check the electrodes for signs of abnormal firing
(3) Remove the Auto Shutdown (ASD) relay from the Power Control Module
(4) Insert the compression gauge adapter special tool 8116, or equivalent, into the #1 spark plug hole; connect the 0-500 psi pressure transducer to the DRBIII®
(5) Crank the engine until the maximum reading is reached on the pressure gauge, then record this pressure
(6) Repeat step #5 for the remaining cylinders
(7) Review all of the compression readings; their change from cylinder-to-cylinder should not vary more than 25%
(8) Repeat the compression test for the cylinder(s) with the low pressure; if the pressure reading is still low, that is a good indication that a problem exists with that cylinder

A visual test can also be performed. This simple test involves removing the coolant pressure cap (when the engine is cold). Start the engine and allow it to warm to a normal operating temperature. If a large combustion/pressure leak exists, bubbles will be visible in the coolant.

There is another test that can be performed using the cooling system. Remove the coolant pressure cap (when the engine is cold) and install the Cooling System Tester 7700, or equivalent. Start the engine and observe the pressure readings on the gauge of the tester. If the gauge reading pulsates with every power stroke, there is a combustion chamber pressure leak.

The tests detailed in this article do not pinpoint head gasket failure specifically; however, head gasket failure can easily be detected when the cylinder head is removed. If the head gasket is bad, the damage will be clearly evident. If it is a valve problem, the head gasket will be intact. In either case, the cylinder head has to be removed to verify the actual problem.