ox66 losing gear oil

[Triton420]

Will use the boat a 5-7 times, check gear oil and will be anywhere from 1/2-1qt low. Almost empty at that point... No water in the oil either.

I have no visible leaks anywhere and nothing on the ground or lower unit. I just removed the prop and thrust washer, replaced the water pump. No oil or residue anywhere on the prop shaft or driveshaft seals. Drain n fill plugs are always tight and dry, prop shaft is not bent.

Any ideas? Has me scratching my head. I have had propshaft seals leak and can always see the leak

[Amistad Tackle]

Since no one has answered I think you can loose oil through the prop shaft seal while running and not know it on Yamahas. I think that seal faces out and is good at keeping water out, but not as good at keeping the oil in. Think there are two seals. This has been discussed on here before. Someone more knowledgeable can give you the details.

[McQuaig]

Amistad is correct. On Yamaha both seals face outward to keep water out, (unlike OMC who face the seals in and out). So if they're worn or prop shaft is bent, the gear oil can get out when running...

[Triton420]

Interesting. Looks like I will rig something up and pressure test it to see if I have a leak under pressure.

[javelin90]

Word of caution, keep pressure about 12psi. Don't exceed 15psi as you will run chance of blowing seals. Use a hand pump to pressurize lower unit. Not compressed air.

[javelin90]

I meant to type also,that when you pressure the lower unit, it is best to remove it from the motor. You want to make sure if it is leaking that it is not the shaft seal on top of motor.