9.9 Mariner vent screw

[accord_guy]

Still having trouble finding a vent screw <br /> for a 91 9.9 Mariner. Parts stores keep trying <br /> to sell me a screw that's too small. My s/n is 0C141585. Anyone know if this was a special case? I just can't seem to get a good seal. The opening is tucked right under the cavitation plate. I'm trying to use an ss screw with a fiber washer and teflon tape. After boating, water is in the oil and it's pushing out from around the vent screw. Any advice would be greatly appreciated.

 

[WillyBWright]

Re: 9.9 Mariner vent screw

Lose the teflon tape. I find it is more likely to allow oil to seep between the plug and housing. The gasket is the sealing mechanism, not the threads. Make sure the sealing surfaces are true. I always replace plug & vent gaskets on lube changes. I'm thinking that the upper driveshaft seal is leaking and forcing water from the water pump into the gearcase. That would account for the internal pressure. Propshaft seal leaks tend to draw pressure out.

 

[accord_guy]

Re: 9.9 Mariner vent screw

Thanks WillyB, <br /><br /> I now have something to look at. You guys are <br /> the best.

 

[Grant Brown]

Re: 9.9 Mariner vent screw

When I drained the case on my '87 70 Hp, the synthetic was all cloudy and some waster came out. While reading this post I noticed a reference to fibre washers. My boat has rubber o-rings on the fill and vent screws. When I fill the case and install the vent screw, oil will pour out when I remove the filler pump. Is this normal? I thought that it should be like holding water in a straw with your finger on the top end so nothing runs out.<br />Where is the next logical place to look for a leak? It doesn't drip any oil even when sitting in the sun all day.<br /><br />Grant