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Author Topic:   water in lower unit oil
boatdryver posted 04-25-2007 11:05 AM ET (US)   Profile for boatdryver   Send Email to boatdryver  
When I started to drain the lower unit oil (Honda BF 90) for replacement it was milky, indicating water contamination. (The motor had not just been run). The oil level however was normal. I left the oil in the unit so the Tech can see it.

30 hours of operation last season, no groundings. all bolts seem tight and drain and oil level check screws were tight with gaskets intact. Minimal metal shavings on the magnetic drain screw tip.

This is a 2001 Honda BF 90 which came on the trailer-kept Montauk I bought a year ago-100 hours total time and the lower unit looks new. Impeller was replaced by an authorized dealer 30 hours ago when I had the motor checked out at purchase and nothing was said about any water contamination at that time.

For flushing I use both the rabbit ear attachment when on the trailer and the screw-in hose attachment up below the cowling when in the slip.

I'm going in for a pressure check of the lower unit to another Honda dealer.

Does anyone have any ideas as to what might be going on?


JBCornwell posted 04-25-2007 11:39 AM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
The single most common cause of water intrusion in the gearcase is re-used gaskets under the drain and vent plugs, Jim.

Many do not realize that they are use-once crush gaskets that are unlikely to seal correctly if reused.

Red sky at night. . .

Livingwater posted 04-25-2007 12:28 PM ET (US)     Profile for Livingwater  Send Email to Livingwater     
I just picked up my supplies last weekend to service my 150 Optimax at home. My dealer gave me new gaskets for the lower unit and said the same thing. "Don't reuse the old gaskets".
contender posted 04-25-2007 01:05 PM ET (US)     Profile for contender  Send Email to contender     
Should only be two places the water can enter the lower unit, The shaft were the the water pump/housing is, or the gear case behind the prop. Unless you have a crack somewere... Sometimes the gasket behind the prop gets some salt behind the gasket(sometimes fishing line can do this) and pushes the gasket out of round, need to pull the gear case for repair. I would bet on the water pump area especially if it was just done, sounds like a bad gasket. If you do not plan to fix it right away I would drain the milk and add new oil...good luck
Legobusier posted 04-25-2007 01:38 PM ET (US)     Profile for Legobusier  Send Email to Legobusier     
I had the same [problem] on my Honda 90 a few years back. Turned out it was the seal at the water pump. A couple of gaskets and a few hours later it was fixed. Replaced the water pump at the same time since it was apart. Pretty easy and inexpensive fix.

Pressure AND vacuum test the unit as pressure tests will sometimes hold seals into place...

Good luck.

Legobusier posted 04-25-2007 01:40 PM ET (US)     Profile for Legobusier  Send Email to Legobusier     
Oh yeah....I wrote this a few years ago - might be helpful

boatdryver posted 04-25-2007 03:08 PM ET (US)     Profile for boatdryver  Send Email to boatdryver     
OK, thanks everyone. Yes I know to always use new gaskets when draining and refilling the gearcase oil. As unneeded confirmation of the need to do this, I noticed that one of them was badly deformed when I removed the screw.

I'll report to the forum when I get the answer. in a couple of weeks.


DAQ posted 04-25-2007 08:24 PM ET (US)     Profile for DAQ  Send Email to DAQ     
I have seen this before also. Most times it was the prop shaft seal being damaged by fishing line.


Chuck Tribolet posted 04-25-2007 09:29 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Those gaskets under the fill and drain will probably work OK
if reused. They are static seals (nothing moving under them).
But I replace them anyway.

If it's pressure tested, make sure they test it under low
pressure (1 PSI and low vacuum (-1 PSI)). Higher pressures
will seat the seals, but low pressure is the way it's running
on the water.


sosmerc posted 04-27-2007 05:00 PM ET (US)     Profile for sosmerc  Send Email to sosmerc     
I agree with Chuck. But always tell my customers to replace the fill and vent screw gaskets just so they can be sure that gaskets are there...often I find customers somehow misplace or lose the gasket during their fill process without knowing it!
And yes, gearcases should be both pressure and vacuum tested at LOW pressure, which represents the actually running conditions that seals must hold against.
Taylor posted 04-27-2007 07:23 PM ET (US)     Profile for Taylor  Send Email to Taylor     
Hey Legobusier, can you repost the picture of your pressure tester? Its missing now.
lurkynot posted 04-28-2007 10:36 AM ET (US)     Profile for lurkynot  Send Email to lurkynot     
It is also possible to add a new gasket to a new or previously used screw all the while the old gasket is lube covered and still in place on the machined face of the lower unit hole. This will will also cause a leak.
boatdryver posted 04-28-2007 11:04 AM ET (US)     Profile for boatdryver  Send Email to boatdryver     
[This article contains] lots of good ideas. Good point about the double gasket. You'd have to be a centipede to see the bed of the drain gasket really well with the motor vertical.

Thanks to all. Pressure and vaccuum testing scheduled May 9 at Honda dealer.

Is anyone surprised that the total fluid level in the lower unit was normal in spite of the admixed oil and water?

Or maybe no surprise since water pressure at the depth of the lower unit is only about 1 psi? (33 ft=1-atmosphere=14.7 psi)--do I have this right?


Legobusier posted 05-03-2007 11:10 AM ET (US)     Profile for Legobusier  Send Email to Legobusier     
Sorry for the dead link...a lot has changed since I first wrote's a NEW and IMPROVED link

boatdryver posted 05-09-2007 11:02 PM ET (US)     Profile for boatdryver  Send Email to boatdryver     
Here's the followup on this problem I promised:

Vaccuum and pressure tests on the lower unit were negative. The Honda mechanic thought that from the appearance of the lower unit oil the amount of water was minimal and he said he "sees this occasionally with different motors". The gasket on the drain screw looked "mangled" and this is the leading theory to explain this event. No flushing of the gearcase was done, just adding new oil. I am to check the appearance of the oil periodically by draining a tiny amount.

Interestingly, they used Yamaha gaskets, which are red rubberized looking material instead of the Honda nylon-looking material gaskets.


Legobusier posted 05-10-2007 08:05 AM ET (US)     Profile for Legobusier  Send Email to Legobusier     
That's good news....just keep an eye on it.

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