If you've ever cracked open an old outboard motor, you know that keeping fluids where they belong is a nightmare without some omc gasket sealing compound on hand. It's one of those old-school staples that hasn't really changed much over the years, mostly because it just works. Whether you're working on a vintage Evinrude or a slightly more modern Johnson, this sticky, brown goop is probably the most important thing sitting on your workbench.
I've spent plenty of Saturday mornings covered in grease, and I can tell you that there's a big difference between a job done quickly and a job done right. Using the right sealant is usually the deciding factor in whether you'll be back on the lake next weekend or back in the garage pulling the powerhead apart again because of a pesky vacuum leak.
What exactly is this stuff?
You might hear people call it "liquid gold" or just "that brown sticky stuff." Technically, omc gasket sealing compound is a non-hardening, brush-on sealant designed specifically for the harsh environments that marine engines live in. It's not like your standard RTV silicone that you'd use on a car thermostat. This stuff stays tacky. It doesn't "dry" into a rubbery solid; instead, it creates a flexible, liquid-tight barrier that can handle the constant vibration and temperature swings of a boat engine.
One of the coolest things about it is its versatility. It's designed to be used with gaskets—especially paper or fiber ones—but it's also great for threaded connections or even metal-to-metal surfaces where a thin film is all you need. Because it doesn't fully harden, it's actually pretty easy to take things apart later. If you've ever had to chisel off old, hardened RTV, you'll appreciate why a non-hardening compound is a gift from the heavens.
Why marine engines need something special
Let's be honest: boats live a hard life. They're constantly sitting in water, shaking like crazy, and getting blasted by salt or silt. A standard automotive sealant often can't handle the sheer amount of vibration an outboard produces. If a seal becomes brittle, it's going to crack, and once it cracks, you've got a leak.
The omc gasket sealing compound is specifically formulated to resist gasoline, oil, and grease. If you've ever seen what gas does to cheap silicone, you know it turns it into a gummy mess that eventually just washes away. This compound holds its ground. It's also excellent at preventing "galvanic corrosion" between aluminum parts, which is a huge deal if you're running your boat in saltwater.
The magic of the brush-in-can
I have to mention the packaging because it's honestly one of the best parts. Most of the time, this stuff comes in a small metal tin with a brush built right into the lid. This makes application way less of a headache. You don't have to go hunting for a popsicle stick or a Q-tip to spread it around. You just unscrew the cap, give it a little stir, and paint it on.
It's messy, though. Don't get me wrong. If you get this on your fingers, you'll be smelling it for the rest of the day, and it doesn't just wash off with soap and water. I usually keep a rag soaked in a bit of isopropyl alcohol nearby just in case I get a little too enthusiastic with the brush.
How to use it without making a total mess
Even though it's a simple product, there's a bit of an art to applying omc gasket sealing compound correctly. You can't just glob it on and hope for the best.
- Clean the surfaces: This is the most important step. If there's old gasket material or oily residue on the metal, the sealant won't bite. I usually use a plastic scraper (to avoid gouging the aluminum) and some brake cleaner to get the mating surfaces bone-dry and shiny.
- Apply a thin coat: You don't need much. Use the brush to apply a thin, even layer to both sides of the gasket. If you're not using a gasket and just sealing threads, a light coating on the threads is plenty.
- Wait a minute: Let the solvent in the compound evaporate for a minute or two until it gets extra tacky. It shouldn't be "runny" when you put the parts together.
- Assemble and torque: Put the pieces together and tighten your bolts to the manufacturer's specs. Since it doesn't harden, you don't have to worry about a "cure time" in the same way you do with silicone, but it's still a good idea to let it sit for a bit before firing up the engine.
Where should you use it?
It's tempting to put this stuff on everything, but there are places where it shines and places where you should probably put the brush down.
Perfect for:
- Water pump plates: This is probably the most common use. Keeping that water pump housing sealed tight is crucial for keeping your engine cool.
- Crankcase halves: Many older OMC outboards don't use a traditional gasket between the crankcase halves. They rely on a very thin layer of sealant.
- Fuel pump gaskets: Since it's resistant to gas, it's the perfect choice for anything in the fuel system.
- Core plugs and threaded fittings: It works wonders on brass fittings going into aluminum blocks to prevent leaks and stop the metals from seizing together.
Maybe skip it on:
- Rubber O-rings: Generally, O-rings do their job best when they're clean or lightly lubricated with a bit of oil or grease. Adding a sticky compound can sometimes make them swell or prevent them from seating correctly in their groove.
- Head gaskets: Most modern head gaskets are designed to be installed dry. Always check your service manual, but usually, the high heat and pressure of the combustion chamber require a different type of seal.
The "Permatex" debate
If you go into any auto parts store and ask for omc gasket sealing compound, the guy behind the counter might hand you a jar of Permatex Aviation Form-A-Gasket. Are they the same thing? Well, they're very, very similar. They smell the same, they look the same, and they behave the same way.
Many old-timers will tell you they're identical, and for 90% of jobs, they probably are. However, if you're a purist or you're working on a high-value motor, there's a certain peace of mind that comes with using the OEM-branded stuff. It's formulated specifically for the requirements OMC laid out decades ago. Plus, the OMC version often seems to have a slightly better consistency for brushing than some of the generic brands.
Cleaning up the "Oops" moments
At some point, you're going to drip some of this stuff on your boat's pristine gelcoat or, worse, your favorite t-shirt. Don't panic. If it's still wet, isopropyl alcohol or denatured alcohol will take it right off. If it has already set up and gotten thick, you might need something a bit stronger like lacquer thinner, but be careful with that around paint.
When it comes time to take the engine apart years down the road, you'll find that the omc gasket sealing compound has turned into a sort of tough, leathery film. It won't be brittle, which is great. A little bit of heat from a heat gun can often soften it up enough to make prying the parts apart a breeze. Just don't go crazy with the screwdriver—aluminum is soft, and you don't want to leave a scar that a new gasket can't cover.
Keeping your can fresh
There's nothing worse than reaching for your can of sealant only to find it's turned into a solid brick of amber resin. This usually happens because the lid wasn't screwed on tight enough, or the threads on the jar got gunked up with dried sealant.
Pro tip: Before you put the cap back on, wipe the threads of the jar with a rag. This ensures a tight seal and makes it way easier to open next time. If the stuff inside starts to get a little too thick to brush easily, you can sometimes thin it back out with a tiny drop of alcohol, but honestly, it's cheap enough that you're better off just buying a fresh can every few years.
Final thoughts on the brown goop
I know it's just a sealant, but there's something satisfying about using a product that's stood the test of time. In a world where everything is made of plastic and designed to be thrown away, a metal tin of omc gasket sealing compound feels like a link to a time when people actually fixed things.
It's reliable, it's durable, and it smells like hard work. If you're doing any kind of maintenance on an outboard, do yourself a favor and keep a can of this stuff close by. Your motor will stay drier, your vacuum will stay tighter, and you'll spend a lot more time enjoying the water instead of mopping up oil from the bottom of your boat. It's a small investment for a whole lot of peace of mind.