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2010 BF40 Leaking oil into exhaust

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Finnn

New member
The 40 hp leaked about a teaspoon of oil through the lower unit exhaust while in indoor storage, in running position (vertical). It is crankcase oil not lower unit gear oil. Could this be from the oil level being maintained too high (always right at top of fill level on dip stick). Could it be from a leaking seal on lower side of the power head? Or something else around the oil pan?
The motor has 517 hrs on it, mostly freshwater except for last 2 yrs, flushed well each time in saltwater. Well maintained, clean, no oil in engine housing, no spilled oil from oil changes or oil filter changes.

Always hoping for a simple solution but kinda nervous about what is going on.

Thanks,
Finnn
 
Hi,
Welcome to the forum.
Yeah, that's a tough one to call and it would bother me too.

The only way of narrowing down where the oil is leaking from, that I can think of, would be to run some dye in the oil.
You would then need to let it sit for a time then pull the gearcase and see if the dye shows up mostly on the inside of the exhaust pipe or not. Kinda, sorta a real PAIN!

If the oil is pooling up under the valve cover, it could leak by an exhaust valve stem and possibly cause this.

I see that the oil for this head drains back to sump via a hose at the bottom of the vc.

Item 1 in the link below.

Honda Outboard 40HP OEM Parts Diagram for Primary Gear Case | Boats.net

Buy OEM Parts for Honda Outboard 40HP Primary Gear Case Diagram
www.boats.net www.boats.net

You might just want to check out that hose to see if there's oil pooling up and not draining back to crankcase.

Hoses that carry hot oil, especially ones with bends in them, can break down internally. That has been known to happen in such a way that a torn piece of the inside lining can actually start acting as a "flap" or valve. Or, the lining can fail so as to create a "bubble" inside the hose and block flow too.

And, of course, any sludge or debris would tend to get stuck in those bends.

Do this:
Run her up to temperature and shut her down then take that hose off. Pretty much all of the oil should be drained out of there within 4 or five minutes at the most.
If not, then more investigation is required.

Good luck.
 
Hey thanks for the advice. I'll follow thru and report back as soon as I get a few things back together (was mid-stride in some maintenance replacing a water pump impeller and thermostat). Just waiting on delivery of parts.

Finnn
 
Hey well, since you have the gearcase off, if you can shine a light up inside the extension and see the exhaust pipe sticking down, look for oil residue inside it. Also scan around the inside of the case and look for residue anywhere else. If you find oil in the case interior then that might suggest an oil leak in another location.

Good luck and hope to hear back soon.
 
Will do. Found the base of the composite water pump housing (under the metal impeller cover) wasn't looking great so had to order that in addition to the housing that came in the rebuild kit) Hopefully that is the last parts order for the project.
 
Well sir,
If you didn't have a new drive key included in that kit, I urge you to get one coming. If you look very closely at your old one, it will have wear and that isn't good.
 
That's good!

I think Honda has gotten a bit better about including "necessity parts" in their (very expensive) kits.

But I've been burned enough in the past by opening up a box expecting that "there's no way they wouldn't include that" only to find I need to order it and wait some more.

The absence of a new drive key in a "complete pump kit" or... not included...the $0.16 screw (82 cents retail) that secures the internal anode that costs $12 to buy and $20 to ship has always galled me.
 
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