Pressure test sterndrives

frenchship

Would a vacuum test on a sterndrives be as good as a pressure test ?
Thanks

Handymans342

Well on an AC system it is easier to find a leak under pressure. A vacuum test can sure tell you if you have a leak or not but a sterndrive is never under a vacuum nor I doubt a lot of pressure either.

Michael T

I certainly hope a stern drive wouldn't operate under a vacuum (for obvious reasons) but do agree that a vacuum test should show a leak (on anything). I would be careful applying too much pressure or vacuum to the drive for fear of displacing/damaging seals. I'd proceed gently. Out of curiosity @frenchship what are you trying to determine, is your gear lube going down in your reservoir or is there a sheen on the water surface near your drive?

frenchship

I guest you are right be easier to find a leak under pressure according to Mercruiser it should hold 10 to 15 Psi for  many hours. Why I ask it is because I do have a vacuum gauge tester with an attached pump, but I guest it would show a leak but could be hard to find where it is leaking
thanks

frenchship

Michael, no leaks just would like to test as a precaution part of maintenance.

Dream_Inn

Most marinas offer a pressure test on drives as part of maintenance, so I see no reason it would hurt.

MDboater

Vacuum limits the amount of stress that you can put on the system to about 14.7 psi (you can't evacuate below 0).  Wouldn't there also be a concern with drawing contaminants into the drive when applying a vacuum?

Michael T

@frenchship, you raised a good question. My electronic copy of Boating Magazine just arrived this morning. They list their top 10 tips for stern drive winterization maintenance. One of them was stern drive pressurization AND vacuum test to test for leaks. That was a new one for me!

frenchship

I did pressure test every spring, but that why I ask about a vacuum test if it was the equivalent of a pressure test, but my understanding was it would be easier to find a leak with a pressure test.
by the way if somebody those a pressure test  with a sterndrive with a remote oil reservoir make sure you pinch or close the the hose going to the reservoir otherwise you would be looking for a leak that does not exist at the sterndrive.

bluto

It's very common to have two seals next to each other. One seal keeps the gear lube in, the other seal keeps water out. Pressure testing checks the "gear lube" seal, vacuum testing checks the "water seal". This is the system used on the OMC Cobra sterndrive. 

boattech01

vacuum test are used on omc and volvo drives. mercruiser u-joint seal only only has a single lip seal for keeping lube in. that is why there is no vacuum test for mercruiser. 

frenchship

Thanks for the Infos.
Paul

rasbury

Hmmm....very interesting Al.....I recently had issue with the outer prop seal that was visibly starting to leak. I had the seal replaced but he did not do any further testing. I have added some fluid as expected, topped it off a couple of times but the reservoir seems to stay at the bottom level. I have stopped topping it off to see if it gets low enough to trip the sensor but so far it has not. There is no visible leaking at the dock or oil feel on the out drive (Bravo III) and your above explanation good be my culprit- it's being sucked out while under power but at "rest" or idle, not pulling any fluid. How wold I verify that inner seal? When the prop shaft seal was replaced, would that visually been available to look at an inspect? The whole carrier bearing assembly was pulled to do the prop shaft seal....

MarkB

I had an undetectable leak. Pressure test was okay. When I was operating the boat it would drain. We replaced the seals and no more drain. Definitely the prop was pulling fluid out when at higher speeds. Problem gone now.

frenchship

Ras.
here is the picture of the seals I think Al is talking about one would be no: 37 and the other 
no: 42.

boattech01

I had a test tank made at work so I could pressure test the drives while sealing areas are under water. I pressure test drives at 10 psi then start lower the pressure 2 psi at a time. I have found several leaks at low pressure that higher pressure did not show.

frenchship

How do you explain that a leak would occur at 2 psi and not at 10.
thanks

MarkB

Funny you say that TJ.  I experienced my gear lube losses when I was running at idle trolling during fishing.

Michael T

A 2011 B lll  I had was doing what was described above by Al. The props were creating negative pressure at higher rpms, causing a leak of gear lube. It was a bugger to detect because when I dripped to lower speeds it must have washed the lube off the drive so I never saw a sheen on the water, until one time when tubing I came off plane fast and someone sitting on the aft seats said there's a sheen on the water. The marina tech replaced the seals. Done.

boattech01

you have to remember the seals are angled and made off rubber the more pressure you apply the tighter the seal will get around the shaft provided the seal is in good condition. where i have found most low pressure leaks is the seal has aged . remember it is rubber so it is getting harder. the higher pressure will still expand the seal enough to seal where lower pressure wont . another factor is if you look at a shaft the seal actually cut a grove in the shaft itself. in saying that it would take more pressure to expand the seal to fill in the grove where less pressure would bypass.

Dream_Inn

Very interesting thread.  I now know of another place to look if I have drive leaks.  I also am more informed when I get my drives pressure tested. Thanks!

rasbury

that is a pretty complex outdrive....I will continue to monitor mine and hope for the best. Being a 2005 boat, guess very possible this is my issue for sure...yuk. I guess as long as I keep topping it off and I'm not pulling any water in, I will continue to watch it- I'm sure something else will go wrong with it and then I will just put all new seals in it at that time. And it may well be ok now and settled down from the re fill of the drive, we'll see!