Using silicone as an adhesive is a bit tricky to get satisfactory results. It is often used for joining together different automotive components like transmission pan, valve covers, differential cover or any part that needs to seal the fluid therein in the absence of any gasket. Here is how to proceed:
Using sandpaper or wire brush, clean the gasket surfaces thoroughly. As a result of such systematic cleaning the metallic surface devoid of any residual gasket should be visible. To ensure the required level of cleaning, wash the cleaned surface with acetone or lacquer thinner. It doesn’t suffice to use other chemicals like Chemtool or break clean, as these are unable to reach the metal pores to remove the old oily residues. Ideally, one should use only lacquer thinner, though Acetone is a good substitute to get satisfactory results. Allow the two surfaces to get dried.
Apply a droplet of about quarter of an inch to the surface. This size of droplet is sufficient for a length of about one inch. So, you need to apply such sizes droplets at a gap of an inch along the surface.
Example: If you have a mating surface of two inches width, use two-quarter inch beads along the surface. Note that silicone needs to be applied on one mating surface only. You have to remove any screws or bolts from the surface before the application of adhesive. Now, position the item to be sealed over the parent surface. On getting compressed silicone will squeeze out from the side. Fix the screws and it’s all over. Let the whole thing get dried for 24 hours. This surely seals the peskiest leak. Anytime you like to take away the item, you may need dynamite.
This is the most practical way for items that are too difficult to be sealed and for surfaces that already have a gasket that did not seal the gasket totally. Many a time you could clean the gasket or mating surface groove and seal the gasket surface without taking away the item. It’s easily understandable that when used in this fashion the process is not as dependable as it would have been had it been used properly. Another helpful hint is that silicone surfaces can be smoothed out, if needed, by just moistening your finger and using the same to even the silicone surface. Normally it is needed for exposed sealant surfaces only and can easily be avoided on mating surfaces that get hidden from view.
By no means use silicone that smells of vinegar. The odor is due acetic acid, which harms oxygen sensors of modern cars. Develop the habit of patronizing only such silicone adhesives that have no content of acetic acid and thus odor of vinegar.