Use of silicone sealer when installing lower unit?

[hkeiner]

I plan to replace the impeller on my 1996 150 HP Mercury Outboard (Serial OG397853). This will be the first time that I have done it myself. I have read the Mercury Service Manual and pretty much know what to do regarding the removal of the lower unit and replacement of the water pump parts. I am a little unclear, however, about the steps for replacing the lower unit.

The manual instructs that a thin bead of silicone should be applied before installation of the lower unit. The manual, however, does not have a diagram or photo showing exactly where to apply this silicone. Also, I have read a variety of generic how-to posts on impeller replacement and they never mention the application of silicone when re-installing the lower unit.

Any comments on the use of silicone would be appreciated.

 

[Laddies]

Re: Use of silicone sealer when installing lower unit?

It goes on the web between the water pickup and exhaust cavity

 

[hkeiner]

Re: Use of silicone sealer when installing lower unit?

I am not sure exactly what the web between the water pickup and the exhaust cavity is. I have not yet taken the lower unit off my motor but I did find a photo of another Mercury lower unit on the internet as an example. See attached.

I highlighted two areas on the lower unit. I think that the intended web is circled and labeled #1. Is that right?

If so, does the silicone go only between the two small holes at either end of the web or should the silicone surround the holes and reach the outer edge of the lower unit?

Thanks

<a href="http://photobucket.com/" target="_blank"><img src="http://i27.photobucket.com/albums/c169/hkeiner/Mercury%20Lower%20Unit/Mercurylowerunit_markup.jpg" border="0" alt="Photobucket - Video and Image Hosting"></a>

 

[gss036]

Re: Use of silicone sealer when installing lower unit?

http://www.in-depthangling.com/foru.../page/0/view/collapsed/sb/5/o/93/fpart/1/vc/1

Click on the above link, lots of pictures so it takes a little time for a dial up connection.

 

[hkeiner]

Re: Use of silicone sealer when installing lower unit?

Gary,

The pictures are very good. However, none of them show the application of any silicone sealer to any part of the lower unit prior to installing it.

Is it possible that the silicone is an unneccessary step (although mentioned in the Mercury Service Manual for my motor) or perhaps is it specific to my outboard model but not to most others?

 

[gss036]

Re: Use of silicone sealer when installing lower unit?

I can't answer that one for you, I have never seen silcone used. Maybe if there was a screen or something in there it would hold it in place.
I just checked my OEM manual and they show silicone being used on the divider block, which I presume is down inside the house under the pump housing. It does not appear to be related to the water pump.

 

[Texasmark]

Re: Use of silicone sealer when installing lower unit?

Never heard of it.

Mark

 

[gss036]

Re: Use of silicone sealer when installing lower unit?

Mark, I had never heard of it either, that is why I checked the manual. It shows a tube (D,silicone) and arrows pointing to #45 which is named the divider block. Not sure of why or what it supposed to seal.

 

[uaw9fan]

Re: Use of silicone sealer when installing lower unit?

# 1 in the posted picture is the correct location. Just apply a bead from the inside of one hole to the other.
I believe the silicone is there to prevent exhaust from being sucked into the water pump. When you remove your lower you may see the old bead.

 

[ncfish1]

Re: Use of silicone sealer when installing lower unit?

The picture you have with #1 circled is the correct location for silicone and it is there to separate the exhaust from the pump area. Not sure why Merc. left the separation point, but it's there.
Make sure your silicone is for below water use.
Apply a level bead from hole to hole and allow to cure "before installing" the lower unit. You want the bead to compress against the upper housing when the two are mated.

 

[hkeiner]

Re: Use of silicone sealer when installing lower unit?

Thanks for the advice. I will follow it.

As a side comment, I wouldn't have thought that silicone sealer would hold up to the hot exhaust gases and seal adequately in that location. That is why I was so uncertain as to how/where to apply it. The advice on letting it cure before installing the lower unit makes sense. I am surprised that the Mercury Service Manual doesn't mention the curing part or go into more detail on the seemingly important step of applying the silicone sealer.

Thanks again.