Lower Unit Oil coming out of prop when servicing

DaveG

DaveG

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Any Help Appreciated! I was servicing my 150 4 Stroke Yamaha with proper fluids and as I topped it off I noticed fluid coming out behind the prop. Put a little too much in. I immediately stopped and screwed the service plug back in and ran the engine with the ear muffs on. I just had the water pump changed and water was flowing just fine
Any need for concern here that I blew a seal over servicing the lower unit?

:uhm
:-|
 
DaveG said:
Any Help Appreciated! I was servicing my 150 4 Stroke Yamaha with proper fluids and as I topped it off I noticed fluid coming out behind the prop. Put a little too much in. I immediately stopped and screwed the service plug back in and ran the engine with the ear muffs on. I just had the water pump changed and water was flowing just fine
Any need for concern here that I blew a seal over servicing the lower unit?

:uhm
:-|
Click to expand...

From what you wrote, it sounds like you removed only one screw/plug (likely the top one?) from the lower unit and pumped (forced, in this case) gear oil in? If so, you may have blown a seal out, or you may have simply just forced oil past the propshaft seals without dislodging them. The proper way is to remove both screws (drain/fill and vent), drain the old gear oil out, and then pump from the fill hole till it comes out the vent. The gearcase should NOT require "topping off" - that is not a normal practice to do.
 
Yes, I put the top screw in as I was getting almost full which seem to cause a little pressure in turn oil coming out. Should I have a pro look at it?

Thanks for the Reply!!!
 
Chances are probably good that everything is OK. But at the cost of bunch of "boat bucks", I certainly wouldn't want to mislead you. It might be best to have it looked at, if you're not comfortable pulling the props and the lower unit to check the prop, drive and shift shaft seals. They may just pressure test the drive - I'm not positive on your lower, but more and more there's no real "spec" for pressure testing anymore on many manufacturer's drives. It's always struck me as strange, but I guess it is what it is.

Good luck! Hopefully it's nothing.
 
Your LU should hold 15 PSI without leaking. If you used a hand pump, it is not likely that you could pressurize that much. Oil coming out of the prop rear usually means that the a seal is shot. As mentioned, oil should be pumped in from the bottom hole and with the top plug removed. As soon as oil starts to run out of the top hole, you have added enough oil. Replace the top plug first before unscrewing the fill hose from the bottom. That helps slow down the flow from the bottom when the fill hose is removed but regardless some oil will leak:)

One thing to do next time is to roughly estimate the amount of oil that drains out by using a container that allows you to estimate the volume. My LU holds about 1.1 quarts of oil and if I don't drain at least a quart, I would suspect that oil has been lost during normal operation and further investigation is in order.
In your case, you have to remove the prop ( you should do that every season anyway to check for things like line wrapper around the shaft) and inspect the shaft seal for evidence of leaks.
The only true test of the LU is a pressure/vacuum test. There are two seals on the shaft: One keeps oil from leaking out and one keeps water from leaking in. For the later, a vacuum test is required.
Of course if you saw water in the drained oil, you don't need a vacuum test, you need seals. Keep in mind that there are other seals than can leak. The drive shaft seal and the shifter seal. Leaks are hard to see with the LU attached but will show up with a pressure test.
 
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