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90 Johnson, gear oil leaking from spedometer hole on lower unit

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90Johnson

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I have a 2000 90hp Johnson that has just started leaking gear oil out of the small hole at the very front of the lower unit. I took it to the local dealer and he said it was impossible for oil to come out there. he drained the oil, which looked slightly milky right away but soon cleared up, and pressure tested to 15 psi, looked at his gauge for maybe 15 seconds and said it is holding pressure and is good. He filled it with oil and told me it must have been unburnt oil and gas and sent me on my way. The motor has not been ran or in the water since, and within 2 days there is clean fresh gear oil coming out of this little hole. What should I do next?
 

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I retired in 1991 so your 2000 engine design is somewhat foreign to me, however some problems such as this (yours) are common to all engines, hence my jumping in here.

I looked at your pictures and it's hard to tell anything that close up... BUT... yeah, it does have the appearance of a glob of heavy consistency fluid such as oil.

Normally that plastic/nylon speedometer fitting has a cap on it to keep anything out of it, however in this case it could be a great $$$ saver (warning).

If it was indeed a bit of non-burnt fuel/oil mixture running down the interior of the long exhaust housing which is a common happening, one can usually have it on their finger tip and smell the fuel portion of it... however your pictures depict a heavier solid oil look, and the slight bit of milky substance when the lower unit was drained indicates the leakage has just started, and as such, if it were me.........

I would suspect either the sealing "O" Ring of the Shift Rod, or a failing driveshaft seal... possibly a shift rod seal housing gasket if it exists but this is unlikely. One or all of these would (I think) have a passageway to that speedometer fitting.

At any rate, that bit milky substance would be enough to have me dropping the lower unit for a visual inspection.
 
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If I had to guess, I'd say at one point water was trapped in the passage for the speedo pickup, it froze, and created a crack into the gearcase. Now, why it passes a pressure test baffles me a bit, but who knows.

Disconnect the tube from the back of the speedometer and blow air at about 5-10PSI through it until you get nothing but air coming out at the leg. Now, let it set for a day or two and see if gear oil leaks out again. If it does, you definitely have a crack somewhere.

You can also blow air right into the nipple at the top of the leg if that's easier.

lowerunit.JPG
 
kevinj said:
If I had to guess, I'd say at one point water was trapped in the passage for the speedo pickup, it froze, and created a crack into the gearcase. Now, why it passes a pressure test baffles me a bit, but who knows.

Disconnect the tube from the back of the speedometer and blow air at about 5-10PSI through it until you get nothing but air coming out at the leg. Now, let it set for a day or two and see if gear oil leaks out again. If it does, you definitely have a crack somewhere.

You can also blow air right into the nipple at the top of the leg if that's easier.

View attachment 18741
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I really hope it is not a crack. The boat is always stored in the same place in the shed and this is the first there has been an oil spot on the floor. Have not had freezing temperatures for months and the boat has been used quite a bit this summer, so my hope is if it was a crack it would have shown up before now. Will have to inspect further and see what I find. It it would be a o-ring or a seal on the shift shaft as the others mentioned, could the oil get to this speedometer passageway?
 
The hole in the front provides pressure to the speedometer if boat is equipped with one.-----So it is a closed passage way.----Oil should not be in there.---Time to do a pressure test on the gearcase.
 
racerone said:
The hole in the front provides pressure to the speedometer if boat is equipped with one.-----So it is a closed passage way.----Oil should not be in there.---Time to do a pressure test on the gearcase.
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Exactly, there should be zero connections between the speedo passage and the gear cavity and therefore no gear oil.

I just re-read the original post and I think it cleared my confusion. The shop pressure tested the case and said there was no issue after holding pressure for 15 seconds. That's not long enough. A proper leak down test would pressurize the case with a gauge connected to the top fill hole and be allowed to set for some time, maybe 30 minutes or more, and then observe to see if the pressure went down.

The other thing you can do is rig up a gearcase pressure tester. Next, disconnect the speedo tube from the nipple at the top of the gearcase and blow air through to evacuate all oil from the pickup passage. Now, using the top fill hole, put about 15PSI pressure on the case with gear oil in it, and observe the bottom intake hole of the water pickup. If you start to see oil dripping from that and your pressure in the gearcase goes down, that means you have a crack in the case somewhere.

It could be the crack happened in the past and over time it's just now getting big enough to show up. So what do you do now? If you want to go cheap you could clean out the top and bottom holes on the speedo passage really well with carb cleaner then fill them really well with JB weld and never use the speedo pickup again. The expensive option is to replace the gearcase (or swap your innards to another gearcase housing). To my knowledge there would be no good way to find and repair that crack.
 
kevinj said:
Exactly, there should be zero connections between the speedo passage and the gear cavity and therefore no gear oil.

I just re-read the original post and I think it cleared my confusion. The shop pressure tested the case and said there was no issue after holding pressure for 15 seconds. That's not long enough. A proper leak down test would pressurize the case with a gauge connected to the top fill hole and be allowed to set for some time, maybe 30 minutes or more, and then observe to see if the pressure went down.

The other thing you can do is rig up a gearcase pressure tester. Next, disconnect the speedo tube from the nipple at the top of the gearcase and blow air through to evacuate all oil from the pickup passage. Now, using the top fill hole, put about 15PSI pressure on the case with gear oil in it, and observe the bottom intake hole of the water pickup. If you start to see oil dripping from that and your pressure in the gearcase goes down, that means you have a crack in the case somewhere.

It could be the crack happened in the past and over time it's just now getting big enough to show up. So what do you do now? If you want to go cheap you could clean out the top and bottom holes on the speedo passage really well with carb cleaner then fill them really well with JB weld and never use the speedo pickup again. The expensive option is to replace the gearcase (or swap your innards to another gearcase housing). To my knowledge there would be no good way to find and repair that crack.
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Thank You, that does make a lot of sense. If it comes down to it, I would definitely try the JB weld option. Where would I JB weld the top hole shut? Remove the lower unit and find the hole there? or take the plastic fitting out that the rubber hose is attached to and JB weld that hole shut? Im not there to look at the motor right now, it may be obvious when I look at it, but you have been very helpful, so just thought I'd ask.
thanks
 
I have seen this problem 3 times in 10 years. The first one took me several days to figure out where problem was coming from. What happens is debris clogs water tube and it freezes. What happens then is the ice pushes up a aluminum plug inside the gearcase under shift housing cover. The plug is where they drill passage for speedo. When pressure tested the plug is pushed down and seals thus not showing leakage. When vacuum testing it will show up but I thought I was having a seal issue of sorts. Long story short when I plugged both the external speedo passages leak stopped and then discovered the plug. The fix is to drive it down and peen in place, I now do this to every gearcase I reseal with a speedo passage whether it leaks or not....
 
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faztbullet said:
What happens is debris clogs water tube and it freezes. What happens then is the ice pushes up a aluminum plug inside the gearcase under shift housing cover. The plug is where they drill passage for speedo. When pressure tested the plug is pushed down and seals thus not showing leakage. When vacuum testing it will show up but I thought I was having a seal issue of sorts. Long story short when I plugged both the external speedo passages leak stopped and then discovered the plug. The fix is to drive it down and peen in place, I now do this to every gearcase I reseal with a speedo passage whether it leaks or not....
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Good catch, I wasn't quite sure how that was drilled out at the factory. Also, it makes sense that it doesn't show up under pressure.

OP, take a close look at this screen grab of the gearcase. Part #'s 53 & 54 are the plug screw and seal for the pitot tube. I guess if you want to be on the safe side you can order a new plug screw and seal and install those to cover your backside since it's already leaking. I guess to cover yourself even more you could apply a little RTV on both sides of the seal but I'm not sure that's necessary if you get a new seal.

Oh, and if that doesn't solve the problem, and you use JB Weld, I guess you'd have to put that material where the plug is and then on the bottom intake side as well.
LU pitot plug.JPG
plugpartnums.jpg
 
I started to remove the lower unit today but am having trouble getting the shift linkage to disconnect. This seems to be a common problem, I thought I tried all the tricks but I can't seem to get it. My motor model # is J90PLSSE looking at the Cylinder and Crankcase diagram I removed the pin #49 and pushed in on #50 but the lower unit only comes down an inch or so. Do I need to remove the bolt from the shift rod lever #81? And the shaft #50 only pushes in so far before it hits the carb, do I need to remove the carb? Any help is greatly appreciated. Thanks
 
When you remove the cotter pin (#49) it should allow the shaft (#50) to slide to the right. Keep the shift rod lever (#81) attached to the shaft. With the cotter pin out you should be able to push the shaft to the right and that will release the shift rod lever pin from the hole in the top of the shift rod . You may need to put a screw driver in there and gently pry between the two to get the pin released. Once you do this you should be able to drop the leg.

I would suggest you thread in a couple of bolts to the mid-section to relieve pressure on the shift rod lever before you pry them apart. If you don't have bolts holding the LU to the midsection it might drop hard and run the risk of busting the gearcase.
 
kevinj said:
Good catch, I wasn't quite sure how that was drilled out at the factory. Also, it makes sense that it doesn't show up under pressure.

OP, take a close look at this screen grab of the gearcase. Part #'s 53 & 54 are the plug screw and seal for the pitot tube. I guess if you want to be on the safe side you can order a new plug screw and seal and install those to cover your backside since it's already leaking. I guess to cover yourself even more you could apply a little RTV on both sides of the seal but I'm not sure that's necessary if you get a new seal.

Oh, and if that doesn't solve the problem, and you use JB Weld, I guess you'd have to put that material where the plug is and then on the bottom intake side as well.
View attachment 18742
View attachment 18743
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Sorry it took so long, but finally replying to what I found with this lower unit. The problem was indeed the sealing washer #54 in the diagram above. I took the bolt #53 out and could see right away that the seal was cut. There was a very sharp edge left by the factory when the threads were tapped in that hole. I smoothed out the edge of the hole and installed a new washer. Have not had any more oil leaking or traces of water in the oil since. Thanks to all of you guys..... I have owned this engine since new and it has been a great motor with very few issues, but I will definitely check back in with you guys when any more issues come up. Thanks again
 
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