Homemade Silicone Gaskets

by David Pepper
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A vexing problem when repairing cars and other machinery is what to do about deteriorated gaskets if replacements aren't readily available. In the past, it was usually necessary to hand-cut a custom gasket out of cork material, but now room temperature vulcanizing (RTV) silicone offers a convenient alternative. Typical applications create custom, homemade silicone gaskets for oil pans, thermostat housings, water pumps and transmission pans. In many cases, a homemade silicone gasket may provide superior performance compared to traditional rubber, cork or paper gaskets.

Choosing the Right Material

Different manufacturers produce RTV silicone gasket makers in different colors. With some manufacturers, the color is strictly cosmetic (for instance, clear silicone to repair electrical wiring and windows, and blue silicone to make gaskets for thermostat housings). Some manufacturers use color coding (red or copper) to indicate special, high-temperature silicone for use in gaskets for hot components such as exhaust manifolds. Avoid RTV-2 silicone, which is a two-part process meant for creating molds, not gaskets.

Preparation and Use

To use, first remove the old gasket by scraping and/or using a gasket remover chemical. The surfaces to be joined need to be completely clean, dry and free of oil or grease. Using the appropriate RTV silicone (regular or high temperature), draw a bead about 1/8-inch wide on one of the surfaces. After wiping away excess silicone, wait about five minutes, until the adhesive develops a light "skin." Then align and mate the parts; do not overtorque bolts. When done, clean off any excess. Before using the vehicle, let the silicone fully set and cure overnight (about six to 12 hours).

Potential Problems

RTV silicones are not recommended for use in areas in direct contact with gasoline. Use high-temperature silicone for parts that run hot. Overtightening bolts can press out the silicone and cause leaks. Don't overapply silicone because excess may ooze into interior parts.

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