Yamaha lower unit oil question

[enfish]

I need some reassurance from the forum here. First, a little background, then my question. A few weeks ago I stopped by the boat and noticed there was lower unit oil leaking from the bottom plug and an oil stain on the ground. My first thought was crap, that's been loose since the last time the motor was serviced a year ago, so we've sucked up a bunch of water. So I tightened up the screw (got a good 1/4 turn on it), and left it to go get some new oil.

It was a couple weeks before we were able to get back to it. So we lower the motor to get it as vertical as possible before hitting the ground and still allowing us to get an oil pan underneath. As the motor tilted down, oil started pouring out of the pitot tube hole, and I started to panic wondering why that is... It stopped after a few seconds, but there was a significant amount of oil that came out. Enough to drip down the side and into the pan. Maybe a couple ounces?

We then proceed to pull the plugs. I was expecting coffee with cream to come out, but the oil looked perfectly clean and new. It was the exact same color as the new oil we put in. We also discovered the top plug was loose as well, and only about 25 ounces of oil came out. We're supposed to take 33.1 ounces. We went ahead and changed the oil and put without any issues.

So my question is, how could oil get into the pitot tube hole? The lower unit was obviously sealed up tight all last year, since no water got in over ~100 hours.

My hypothesis is that someone needed to "borrow" some of our lower unit oil and unscrewed the plugs. Since the motor is stored tilted up and cranked over to port (to keep the steering push-pull rod from being exposed, per the manual), if someone pulled the top plug in that position, oil would pour out the top hole and down the side of the lower unit right over the pitot tube hole. At least, I'm hoping that's the case.... :?

Does anyone else have any ideas how oil could get in the pitot tube hole?

 

[catch22]

Can't imagine what the cause might be, but I would drain it, drop the lower unit and get it vacuum tested. Piece of mind.

 

[freddy063]

is it a 2 stroke? If so check to see if the little oil tank on top of the motor was leaking when you have the motors all the way up. If oil leaked out it would run down in side the motor and try to find it way out somewhere. Just My guess.

 

[enfish]

Thanks for the replies guys. It was definitely brown lower unit oil coming out of the hole, not green 2-stroke Yamalube.

We did pressurize the lower unit slightly by putting the top plug in after it was filled and putting a few more pumps of oil in. The pressure held for an hour or so when we came back to pull the pump off and put the plug back in. Not really a definitive test, so we'll see.

 

[Hookup1]

Lower Unit

Are you sure you don't have a bad shaft seal and a mechanic who forgot to tighten the fill and vent screws?

 

[enfish]

Re: Lower Unit

Are you sure you don't have a bad shaft seal and a mechanic who forgot to tighten the fill and vent screws?

It's possible, and my first thought was the mechanic didn't tighten the screws. But we've put ~100 hours on the engine since the oil was last changed, and there was not one drop of water in the oil that came out. If the plugs had been loose the whole time, that oil would have been full of water. So the screw plugs started leaking after the boat was last in the water. Leaky seals also would not explain how oil got into the pitot tube. It's still a mystery to me....

 

[seasick]

If the vertical drive shaft seal is leaky, oil will seep out when the motor is tilted up. This may be what happened.
Pressure tests have to be done with the lower unit drained. The lower case will be fed with air to about 10 to 15 psi and let sit.
After 10 minutes or more, the pressure should be the same.
A full test also includes a vacuum test where negative air pressure is introduced. This checks for seals that stop sea water from entering the unit. That is probably not an issue in your case.

 

[Tashmoo]

Could someone have used your speedometer tube to try to get some oil out of your lower unit and then reattach it? Will the tube pull down that far? If yes this tube could have got oil in it which flowed back into the pitot tube. Better yet why would someone go through that much effort.

The other possibility but a very long shot is that the oil ran down the apex of the lower unit over the pitot tube opening and got pulled into the pitot tube by a negative pressure in the speedometer tube caused by day night temperature swings and corresponding changes in the specific volume of air in the tube. But that would only account for a very small volume of oil.

One thing is for sure someone screwed with your plugs as you would have had a milkshake in you lower unit with both plugs loose and 100 hour of run time.

PS from bitter experience change your lower unit oil before winter storage. If you have water in the oil it can freeze but it will also do a number on the bearings, trust me I made that mistake once.

 

[enfish]

PS from bitter experience change your lower unit oil before winter storage. If you have water in the oil it can freeze but it will also do a number on the bearings, trust me I made that mistake once.

Southern California... 12 month boating season, and no ice :wink:

I'm definitely leaning towards someone tampering with the lower unit. We'll see if anymore oil ends up dripping out the pitot tube hole again next time the drive is lowered.

Your long shot possibility actually does make sense since gravity could make the oil run down into the hole the way the motor is angled, if someone pulled the top vent plug and oil poured out of it.

Thanks for all your help guys! I feel better that no one has heard of this before. It doesn't make me happy, but it wouldn't be the first time the boat has been tampered with in the storage yard, so I can deal with it... as long as no major damage occurs.

 

[enfish]

If the vertical drive shaft seal is leaky, oil will seep out when the motor is tilted up. This may be what happened.
Pressure tests have to be done with the lower unit drained. The lower case will be fed with air to about 10 to 15 psi and let sit.
After 10 minutes or more, the pressure should be the same.
A full test also includes a vacuum test where negative air pressure is introduced. This checks for seals that stop sea water from entering the unit. That is probably not an issue in your case.

I missed this post on my previous reply. Where is the vertical drive shaft seal located?

 

[seasick]

Actually there are three seals in the upper end of the lower unit:Two for the drive shaft which are located below the water pump wear plate under a seal cover. The third is on the shifter rod. There is a cover plate over that one also.
If the drive shaft seals are shot, there is a chance that the drive shaft bearing is worn causing side to side play that wore the seals. You might be able to see side play after the water pump and housing are removed. Regardless, if either of the two shafts are leaking, you will see oil near the shifter rod or under the water pump.

 

[enfish]

Thanks Seasick. I've got a good mental image of what you're talking about. Good info there!

 

[JUST-IN-TIME]

Bad drive shaft seals = oil out the water intake screens

Bad shift shaft seal = oil out pilot hole

 

[enfish]

Thanks Richie! Is the process of changing out the seal too involved, or is it a relatively simple procedure?

 

[JUST-IN-TIME]

shift shaft -ez

drive shaft a little harder

 

[enfish]

Thanks again Richie. Am I correct in thinking that even if the shift shaft seal was leaking, water would not necessarily get into the oil since it's leaking into the upper housing? I'm still a bit confused that how if a lower unit seal was leaking, no water would be in the oil.

 

[JUST-IN-TIME]

pressure test it

 

[seasick]

Thanks again Richie. Am I correct in thinking that even if the shift shaft seal was leaking, water would not necessarily get into the oil since it's leaking into the upper housing? I'm still a bit confused that how if a lower unit seal was leaking, no water would be in the oil.

There are two seals. On the prop shaft, one seal protects fluids from getting into the housing and one protescts fluids from getting out. It is possible to have one bad seal and get oil leaking without water getting in. I assume but am not certain that the same can happen on the drive seals.
If the motor is stored where the sun hits it, the oil warms up and expands also. That will place a little more pressure on the seals.
You won't be sure until you drop the lower unit and inspect.

 

[enfish]

Update

Hey guys, I just wanted to thank you for all your help. Finally got the lower unit pressure tested and it turned out to be a bad drive shaft seal. Went ahead and replaced that seal and the shift shaft seal as well, since the parts were just a few bucks.

 

[seasick]

Great...
Enjoy