Losing pressure with a pressure test

[TheRussian]

Good morning,

I have performed a pressure test with a home-made tester after changing the water pump on my alpha one gen 2.

Pressure dropped from 15psi to 12.5 psi in a 4 hour time-frame.

I cannot hear any air escaping from the outside of the gear case. My home made tool connects to the case via a plastic connector that came with an oil change pump, and I am using the same clear hose. I have also added a metal clamp on the plastic fitting to secure.

I am wondering if 1. the air may be escaping somewhere in the connections of the tool itself or where the plastic fitting connects to the vent hole (or the clamp does not completely restrict air loss, or some other cause); 2. if the pressure drop is it still within an allowable limit given that the drop was over 4 hours and there is no noticeable drop within a shorter timeframe (ie. 10 mins).

I am really hoping to avoid a complete teardown as I am learning one thing at a time, and this would be skipping ahead in my boat-owning education.

Thanks

 

[flipbro]

Put some dish soap and water in a spray bottle and spray the connections. If that's not your leak spray anywhere it could leak. If you still don't find it fill your tube up and sumerge it. IMO any leak even small is no good.Drop your pressure to 8 psi it likely leaks a little faster.

 

[nec plus ultra]

Test all connetions of the gear case and your home made tester with soapy water and look for bubble

 

[JoLin]

Put some dish soap and water in a spray bottle and spray the connections.

Start with the pressure tester- everyplace that there's supposed to be an airthight connection. Found my first leak there. Then spray the the drain plugs and dipstick tube. Found my second leak there. Tested both my drives and after fixing the leaking tester connections I needed a dipstick tube gasket on one and a shift shaft bushing on the other. Both simple fixes.

As you fix a leak, you need to re-pressurize and retest.

 

[alldodge]

IMO 15 is to high a pressure, should be in the 8 to 10 psi range. Also for best check is to do a 5 in HG vacuum. I'm thinking your good but as others have suggested, do check it out

 

[TheRussian]

Would it be terribly wrong to hook up the tester to the drain instead of the vent? This would make the submersion test much, much easier.

Just wanted to mention that I replaced the seals on the drain, vent and the dipstick. Also, there were no obvious oil leaks when I had the outdrive removed for water pump service, so I don't think that any seal leak could have been too big(?). The oil was nice and clean when drained.

AllDodge, I will also check at a lower positive pressure, but I am fairly certain that my service manual advises against a vacuum test.

What is the length of time that the drive needs to stay pressurized for? Seems like I have to wait for hours and hours between tests to see if anything is leaking!

Flibro, are you saying that the leak may be more pronounced at a LOWER pressure?

 

[GA_Boater]

Flibro, are you saying that the leak may be more pronounced at a LOWER pressure?

He's saying the seals can be overpressurized. The seals aren't designed to hold large pressures, only keep lube in and water out. The soapy water spray cuts down on the time it takes for testing.

Also while it's pressurized, turn the prop shaft, drive shaft and shift shaft. Some time the seals only leak with motion and the gauge will drop quickly when a shaft is moved.

 

[JASinIL2006]

I agree with JoLin - check the tester and the easily accessed things like the drain, vent and dipstick seals first. My homemade tester had several places where it could leak, and when me first pressure test failed, it was the tester losing air, not the drive.

 

[TheRussian]

So am I OK to connect the tester to the bottom drain plug instead of the vent?

 

[flipbro]

So am I OK to connect the tester to the bottom drain plug instead of the vent?

Yes you can hook it there. Try the 8 psi as well.

 

[TheRussian]

Thanks.

I was able to find a leak at the gauge even though it was on tight with teflon tape. After multiple attempts to fix the problem the leak was finally eliminated. The drive appears to be holding pressure at 10psi

Thanks again everyone.

 

[achris]

...Pressure dropped from 15psi to 12.5 psi in a 4 hour time-frame...

Why are you leaving it 4 hours? Most shops will leave it barely 15 minutes (as per the book). If it shows no leak in 15 minutes, it's good to go. Fill it with oil, slap it back on the boat and go boating.

Chris...........

 

[TheRussian]

Chris,

I am just following what many boaters have posted on forums. I did read the service manual regarding the pressure test but wanted to make absolutely sure. Same thing as the water pump impeller - Merc does not state to replace but it appears that most people do.

Thanks!