See full version: Where to use gasket sealer
I advise against using silicone or permatex on a outboard engine. It simply will not function properly. The exception to this (as per OMC's recommendation), is to use the black Permatex (heavily) on the gasket 306242 which seperates the inner exhaust tube from the exhaust housing on the 1959 35hp and 1960 to 1970 40hp OMC outboards.
DO NOT use any sealer on the large "O" Rings that are used on the upper and lower crankcase heads (The housing/heads that slide over the top and bottom of the crankshaft). On those "O" Rings, use only a coating of grease.
To be honest I'd rather not use gasket sealer as it tends to result in the gasket being destroyed if removed again, but if it's necessary to achieve the appropriate seal then I will.
NOTE: OMC Adhesive is now Bombardier 3M Product #847 .
- reed valve cover / plate
- head gasket
- exhaust gasket (to lower unit)
- carburettor to intake gasket
- driveshaft seal
Also, use it on the outside diameter of all pressed-in seals. more
(Fig. 2) Only apply a very thin bead of gasket maker. A thin bead will spread out and cover the assembly properly. Excess gasket maker can cause it to squeeze out.
However there is one elastomeric RTV gasket maker that can be put back into service immediately, and that’s Permatex The Right Stuff®. This formula allows you to simply ‘torque and go.’ here
Only solvent-based gasket makers have the ability to stand up to repeated direct contact to gasoline. Powersports vehicles, antique cars, gas-powered tools, and equipment all tend to have their gaskets exposed to gasoline. Gas weakens RTV and anaerobic flange sealants. If your assembly will have direct exposure to gasoline, you should use a solvent-based gasket maker. more
2. Using the wrong type of gasket maker for your application.
Gasket makers and flange sealants are specially formulated for specific applications. These formulations are available for a variety of requirements: high temperatures, resistance to synthetic oil, O2 sensor compatibility, water-glycol resistance, and more. Trying to use one gasket maker or flange sealant for every application may not result in a reliable repair. Make sure the gasket maker or flange sealant you use meet the specs for your application.
Completely avoid the use of contaminated or damaged threads. here
Mistake 10: Failure to Check Bolt Lengths [links]
Blown gaskets can be caused by detonation, improper cooling of the engine, or a poor installation.
The recommended torque specs and patterns are important for proper installation.
Any flaws, even the smallest, can result leaks. more
NOTE 1: I am under the impression that Marprox Sealer 1000 and Boat Armor Sealer 1000 is no longer available.
DO NOT use any sealer on the large "O" Rings that are used on the upper and lower crankcase heads (The housing/heads that slide over the top and bottom of the crankshaft). On those "O" Rings, use only a coating of grease. more
Do Not use any type of sealer on outboard carburetor or intake manifold gaskets as this would cause blockage of various fuel/air passageways. Also, there are new type gaskets, including head gaskets, which are used through out the engines that are coated with a substance that gives a shinny appearance to them. These gaskets are coated with a self sealer and are to be installed as is. no sealers! Older style head and fuel related gaskets that are not coated with this substance are to be simply coated with oil. nothing else.
The exception of surface to surface contacts pertains to the later model matching crankcase (block) halves (which does not incorporate spaghetti tubing) which call for "Gel-Seal", or any other surface that calls for Gel-Seal. This substance seals in the absence of air, and if called for, must be used. One other form of Gel Seal that can be substituted is "Loctite #518". Nothing else that I know of will do!
Marprox Sealer 1000 or OMC Adhesive or Boat Armor Sealer 1000 (same substance)[See Below Note] should be used on any metal to metal (Unless GelSeal Is Called For) or metal to plastic surface (such as impeller hsg to plate, and plate to lower unit surface) to eliminate air leaks. It should also be used on the Spaghetti tubing that is used on many powerhead crankcase halves, lower unit skegs, etc. I have found that this substance works quite well on various "O" Rings such as what are found on lower unit carrier and upper driveshaft bearing housings (Note that this substance is obviously not to be used on all "O" Rings). This substance also works quite well in sealing the surfaces between the lower unit and the exhaust housing to which it attaches, eliminating the unsightly water spray between the two after completing a water pump installation. here