Seal the Deal

Gaskets come in all shapes, sizes and materials, but they all have a common mission: To keep gasses and liquids where they’re supposed to be.

Gaskets play a very important role in automotive engines. By definition, a gasket is a mechanical barrier between two surfaces that creates a seal between those two surfaces. This seal prevents the flow of gasses or liquids, depending on the application, between these surfaces.

Gasket Basics

Gaskets are necessary because it is virtually impossible to machine the two surfaces to a flatness and smoothness that will provide such a seal (there are few exceptions to this rule). Gaskets conform to most irregularities in the surfaces to create an adequate seal.

Most gaskets are pre-formed and are made from a variety of materials. These materials include steel, cork and neoprene. Some gaskets are not pre-formed, but are formed when the gasket material is applied to the surfaces that must be sealed. These are known as form-in-place gaskets. Other materials, known as sealers, are used in conjunction with a pre-formed gasket to make the required seal.

The material used for a specific gasket is based on the application. For example, a cylinder head gasket that prevents compressed air/fuel mixture from escaping from the combustion chamber requires a gasket material that can withstand the heat of combustion. On the other hand, the water pump gasket that prevents coolant leaks around the perimeter of the pump housing doesn’t need a high-temperature material, but one that can form a liquid-tight seal.

Gaskets can be either static (or stationary) or dynamic. A static gasket is one that does not move. When you think of a gasket, this is the type that usually comes to mind. Examples include the oil pan gasket and the cylinder head gasket.

Dynamic gaskets seal moving components. The most common examples are the valve stem seal (this seal is mounted on top of the valve guide and on the valve stem; the valve stem moves during engine operation, but the seal remains in place) and the crankshaft seal (this gasket is installed in the engine block. As the crankshaft rotates, the seal stays in place to prevent the flow of oil out of the crankcase). Here, we will limit our discussion to static gaskets.

When you think of a gasket, you usually picture one that is pre-formed and stamped from a particular type of material. One common type of gasket is the intake manifold gasket (see Figure 1). This gasket is the sealing device between the intake manifold and cylinder head in a typical V-type engine (in this case, the 8.0L V-10 truck engine). Other types of common pre-formed gaskets include those used on cylinder heads, timing chain covers and exhaust manifolds.

Form-in-Place Gaskets and Sealers

There are numerous locations on the engine where form-in-place gaskets are used. Special care must be taken when applying this type of gasket to ensure the desired seal. Do not use form-in-place gaskets unless specified. Check the appropriate service manual for the type of gasket and/or sealer required for a specific application.

When applying this type of gasket, bead size, continuity and location are of great importance. If the bead is too thin, fluid leakage can result. On the other hand, if the bead is too thick, spill-over can result, leading to some of the material breaking off and obstructing fluid feed lines. A continuous bead of the proper width is essential to obtain a leak-free gasket.

There are several types of form-in-place gasket materials. These include Mopar® Engine RTV GEN II, Mopar ATF-RTV and Mopar Gasket Maker. Each of these materials has its own distinct properties and cannot be used in place of the other.

For example, Mopar Engine RTV GEN II is used to seal components that are exposed to engine oil. One of its applications is the oil pan. On the other hand, Mopar ATF-RTV is a specifically designed black silicone rubber RTV that retains its adhesion and sealing properties when exposed to automatic transmission fluid, engine coolants and moisture. Finally, Mopar Gasket Maker is an anaerobic type gasket material. It cures in the absence of air when squeezed between two machined surfaces. Do not use it on flexible metal flanges.

Mopar Gasket Sealant is a slow drying, permanently soft sealer. This material is recommended for sealing threaded fittings and gaskets against leakage of oil and coolant. It can be used on all threaded and machined parts under all temperatures.

Engine Gasket Surface Preparation

Gaskets cannot be re-used; therefore, when two sealed surfaces are separated, the gasket used between those two surfaces must be removed and discarded. In order for the new gasket to seal properly between these surfaces, the surfaces must be smooth, flat, dry, clean and free of all traces of the previous gasket.

To ensure proper engine gasket sealing, proper surface preparation is a must, especially for aluminum engine components and cylinder heads that use multi-layer steel (MLS) head gaskets. Here are some important tips:

1. Never use a metal scraper, an abrasive pad or paper to clean the cylinder block and head, or a high speed power tool with an abrasive pad or a wire brush. If aggressive cleaning is required, use a white plastic 3M™ Roloc™ bristle disc (see Figure 2).
2. Multi-layer steel (MLS) head gaskets require a scratch free sealing surface. To clean such a surface use solvent or a commercially available gasket remover. A plastic or wood scraper can also be used.
3. Sealing surfaces must be free of grease and oil residue. Clean all mating surfaces with Mopar Brake Parts Cleaner, or equivalent.

Finally, all cylinder heads should be checked for flatness. This is done using a straight edge and feeler gauge (see Figure 3). As a general rule, the cylinder head must be flat within 0.004" (0.1 mm). Check the appropriate service manual for the specifications for the engine you are servicing.

Installing Gaskets

After the two surfaces that are being sealed have been cleaned, the gasket can be installed. One of the most important aspects of gasket installation is the orientation of the gasket. Check the gasket being installed for markings that would indicate top or bottom and front or rear.

Also, be aware of the construction of the gasket. For example, the 3.5L V-6 engine has perfectly round combustion sealing rings, where as the 3.2L V-6 does not.

Some applications will require the use of sealers with the gasket to form the required seal. For example, on the 3.3L/3.8L V-6 oil pan, you have to apply a 1/8-inch bead of Mopar Engine RTV GEN II at the parting line of the chain case cover and the rear seal retainer. Also, the timing chain cover on 2.7L V-6 requires the use of Mopar Engine RTV GEN II at the parting lines between the oil pan and the cylinder block. The use of sealers at parting lines of many components is common.

Finally, there will be some applications that will require Mopar Gasket Maker. One of these is the oil pump housing on the 2.4L four-cylinder engine. As shown in Figure 4, the gasket maker compound is applied to the sealing surface as shown.

Gaskets are used throughout the engine and gaskets come in all shapes, sizes and materials. If you have any questions regarding the gasket for a particular application, check the appropriate service manual for the vehicle being serviced or consult your Mopar Magazine dealer.