I have an alpha one drive. My gear lube reservoir gets filled to the full level. I check it once in awhile and it goes down to the add mark. I did a pressure test and it came out okay. I have it changed every year. Could there be just air bubbles in the line?. Thank you for any replies. Jj

Year of the app here ? any prop impact ??

propshaft seal or check to make sure its not dripping from the gear oil reservoir bottle were the wires come thru. Common problem for the past 6 years and especially since Merc has this bottle made in Korea of all places. The older bottles lasted for ever but over time they can leak.

Next it can be leaking into your U joint bellows especially when running only from the upper input shaft seal area. Is that portion rusty going into the drive ??? When pressure testing - it is wise to turn the input / U joint shaft by hand as well to see if it leaks then. You have to pull the drive for this and can check for gear oil in the bellows.

Next place for a hard to find oil leak and missed alot is a small cracked in the plastic valve fitting that the gear oil line is connected to externally, its located in the transom assembly externally or the line itself is the leak source - dry rotted or cracked in areas ?

when you pressure tested the outdrive - how did you do it and with what tool did you use ? Did you spin the propshaft by hand in both directions when it was holding air to see if it leaked then - many miss that part of pressure testing the outdrive ?

Pretty normal for the lube level in the reservoir to drop 1-2" in the first +/- 5 hrs of use after the lube has been changed. The small air pockets will work their way out.

The mechanic did it at my marina. I will have to ask him when all the snow is gone here. Thanks for the suggestions. It never went below the add line though. It always stayed at that level

That's what my mechanic said was happening. It would never go below the add line. I think I filled it 2 times that I can remember. It never seemed to go below the add line. So I had my mechanic do a pressure test and he said everything seemed to test out fine, he found no leaks. Thanks for your input
Jj

If you fill the outdrive 100% correctly and then run engine on the garden hose - shift it fwd and rev - then let it sit to recheck the level, it should 9.5 out 10 times be 100 % fine with no level drop unless you have a problem or was filled incorrectly.

Please think about this - every marine shop that serviced outdrive gear oil changes would have their customers bringing all their boats back in for rechecks and level top offs afterwards. Sorry it does not happen that way. Some big shops change 100 gear oils in one week. It needs to be filled correctly or rechecked for leaks.

Brand new outdrives and or just newly rebuilt outdrives can experience level drops more so no matter how they were filled.

Never heard of someone running the boat in forward and reverse to get air pockets out of the drive. Likely because it's probably easier to just run the boat and top off the resevoir as required.

Huh - marine service shops run boats 100 % of time on a water hose supply and shift outdrives in fwd & rev especially after gear oil changes, Impeller changes, and so on. I never heard of marine service shops NOT doing this - its part of the service that the end user pays for -

Service shops are not going to lake test a customers boat for an gear oil change ONLY unles the customer wants them to.

And how does a "professional" fill an outdrive 100% correctly? I'm pretty sure everyone pumps drive fluid in the same...with positive pressure (via hand pump, drill, compressed air, etc). Unless there is a secret no one else knows about. Ultimately it comes down to 2 things, 1. The inherent drive design which dictates how the oil flows upon re-entry and 2. Oil viscosity.

Sorry forgot the third...the fact that when it comes to the top drain one has to close it and guess how much more oil needs to flow such that oil reached the top cap.