Air coming from lower unit?

[surrender]

While at idle in the water I noticed what looked to be a "mist" of tiny air bubbles coming from the seam where the lower unit meets the mid section of my 1996 88 special. Also when I first start it up after sitting at one spot fishing, a bunch of gurgling and air seem to come from the lower unit ares, then it cleans up and the mist starts with an occasional bigger "burp" of air. Is this exhaust getting by the bellows and leaking out the seam between the lower and midsection? I checked the lower unit oil when I got home and it looked good, no signs of water.

 

[Chris1956]

Re: Air coming from lower unit?

Check the seam between the gearcase and the midsection. On my '98 Johnny 150HPV6, there are molded in slots to allow exhaust and water to exit. It is likely you have the same slots.

 

[surrender]

Re: Air coming from lower unit?

Dont think there are slots. If i recall the manual says to use OMC gasket seal of some sort(haven't read it in a while). I did the waterpump a while back and used Permatex gasket seal. Maybe I need to re check manual. Also do you replace the exhaust bellows or reuse? Mine looked good so I reused. It was hard to get it to seat when I was raising the lower unit

 

[bream master]

Re: Air coming from lower unit?

Hi mate,try using permatex it wont hurt it i do,or even marine grease.....CHEERS

 

[F_R]

Re: Air coming from lower unit?

Best thing is don't even worry about it. As already suggested, the early ones were supposed to be sealed when assembled, but later on they actually had slots. Bottom line is it doesn't matter at all. It is only cosmetic. So many didn't get resealed when replacing the water pump that the factory finally said to heck with it, lets open 'er up and make it "normal" to leak. Thus the slots. Even the un-slotted ones have a small opening at the forward end as a drain hole.

 

[surrender]

Re: Air coming from lower unit?

Mine doesn't have slots, but it does have the drain hole forward. So is the air exhaust from the exhaust bellows not sealed just right? One more note, the tell tale stream is very good when running off the hose at the house(I only have the hose running about three quarters open so I dont think the good stream is a result of my house water pressure) but at idle in the water it is not nearly as good. While running it is good anfd the motor runs at the proper temp. Any thoughts. Thanks.

 

[emdsapmgr]

Re: Air coming from lower unit?

Could be. You can leak exhaust gas into the lower midsection if either of the two inner exhaust housing rubber gaskets leak. These are trapezoid shaped type orings, about 1/4 square. The upper one is not as big a problem, but the lower one by the water pump is. If the lower one is missing or leaking (the older these gaskets are, the more they deform) the exhaust gas can come out next to the composite water pump housing-probably not a good thing long-term.

 

[surrender]

Re: Air coming from lower unit?

Could be. You can leak exhaust gas into the lower midsection if either of the two inner exhaust housing rubber gaskets leak. These are trapezoid shaped type orings, about 1/4 square. The upper one is not as big a problem, but the lower one by the water pump is. If the lower one is missing or leaking (the older these gaskets are, the more they deform) the exhaust gas can come out next to the composite water pump housing-probably not a good thing long-term.

When I did the waterpump the lower gasket was difficult to get seated, it kept wanting to pop out as I raised the lower into place. I pretty sure its seated but maybe due to age its not sealing. What is the harm (short term) of this leak? Do you need all the exhaust and water to leave from the prop hub exit? Also, how would one go about pressure testing the lower unit at home?

 

[emdsapmgr]

Re: Air coming from lower unit?

That lower exhaust tube gasket tends to grow with age. When you do drop the lower for servicing the water pump, sometimes the original lower gasket is hard to get correctly seated back in place. If you do get it back in place, sometimes they curl up on one side during final bolt tightening, causing an exhaust leak by the water pump housing. You may want to just replace the gasket. The only issue is the heat from the exhaust possibly affecting (heat deforming) the composite housing over long periods of time. If you take your lower to have it pressure tested at any marine dealer, they will actually do two tests, a vacuum test and a pressure test with special test tools. The lower needs to hold 12 lbs or vacuum/pressure for a half hour to indicate the gearcase seals are ok. A cheaper alternative is to periodically inspect the lower unit oil to check for water intrustion. No water=ok.