I just bought a boat with a 1994 115 HP merc OB and the previous owner pointed out the leaking oil problem when tilted. It leaks out the oil reservoir cap because the gasket doesn't fit properly. From what I've read on the web, most people just don't fill the reservoir to a point where it will leak when tilted. The ones that had the gasket replaced, didn't cure the problem bacause the gasket was manufactured to barely the right size and over a short period of time, it would shrink a bit and the oil would just start leaking out again.
It's an easy fix and here's how. Go to McMaster.com and order a 12 X 12 sheet of P/N 86095K41. It costs a little over $2 and seems to be the exact material as the original gasket. It is oil resistant and is excellent at sealing. As far as the adhesive, I had some 3M Scotch Grip 4475 plastic adhesive laying around that is advertised by 3M to resist oil as well. McMaster sells a 5 oz tube for about $9 (P/N 75285A71). I used it because you can spread it very thin. Through trial and error with many materials and adhesives, I found that any surface deformation in either the gasket or the adhesive layer will cause a leak.
Remove the cowl and open the reservoir cap. Look at the old reservoir cap gasket before pulling it off. See the gap all the way around between the edge of the gasket and the ridge on the lid? That's why it leaks. Pull the old gasket off and use it as a guide to shape your new one. At this time, use Goof-Off or eqiuivalent to get the old rubber adhesive off the cap. Watch out to not get anything in your oil reservoir.
Using a single edge razor, straight edge and the old gasket as a guide, make the new one bigger so it fits perfectly within the ridges. Freehand the curved parts using the original gasket as a guide to start. Nip just enough of the corners of the new gasket so they just fit into the radius in the cap ridges. You want a nice fit where you don't have to push it into the ridges and the corners aren't pinched. Go ahead and put it in place, close the cap and tilt the motor. It it leaks, check out where. Either it is too small in that area or it is pinched. Once it fits right, go wash the gasket off with dishwashing soap (rinse well) to get the oil off. Then wipe it with acetone, then alcohol. Clean the lid with 409 or equivalent, then acetone and then alcohol. Watch out to not get anything in your oil reservoir. Apply a very thin layer of adhesive to both surfaces all the way out to the edge (in case the gasket wants to shrink, this will prevent it), put together and your done. Close the lid and tilt the motor. If it leaks, you used too much adhesive and the gasket's deforming too much. Good luck!
It's an easy fix and here's how. Go to McMaster.com and order a 12 X 12 sheet of P/N 86095K41. It costs a little over $2 and seems to be the exact material as the original gasket. It is oil resistant and is excellent at sealing. As far as the adhesive, I had some 3M Scotch Grip 4475 plastic adhesive laying around that is advertised by 3M to resist oil as well. McMaster sells a 5 oz tube for about $9 (P/N 75285A71). I used it because you can spread it very thin. Through trial and error with many materials and adhesives, I found that any surface deformation in either the gasket or the adhesive layer will cause a leak.
Remove the cowl and open the reservoir cap. Look at the old reservoir cap gasket before pulling it off. See the gap all the way around between the edge of the gasket and the ridge on the lid? That's why it leaks. Pull the old gasket off and use it as a guide to shape your new one. At this time, use Goof-Off or eqiuivalent to get the old rubber adhesive off the cap. Watch out to not get anything in your oil reservoir.
Using a single edge razor, straight edge and the old gasket as a guide, make the new one bigger so it fits perfectly within the ridges. Freehand the curved parts using the original gasket as a guide to start. Nip just enough of the corners of the new gasket so they just fit into the radius in the cap ridges. You want a nice fit where you don't have to push it into the ridges and the corners aren't pinched. Go ahead and put it in place, close the cap and tilt the motor. It it leaks, check out where. Either it is too small in that area or it is pinched. Once it fits right, go wash the gasket off with dishwashing soap (rinse well) to get the oil off. Then wipe it with acetone, then alcohol. Clean the lid with 409 or equivalent, then acetone and then alcohol. Watch out to not get anything in your oil reservoir. Apply a very thin layer of adhesive to both surfaces all the way out to the edge (in case the gasket wants to shrink, this will prevent it), put together and your done. Close the lid and tilt the motor. If it leaks, you used too much adhesive and the gasket's deforming too much. Good luck!
