Correct pressure/vacuum test procedure

[mklearl]

Dp-sm outdrive. I had some water in the oil at the end of the season. I did a pressure/vacuum test according to the manual. Held pressure overnight. On the vacuum test I pumped to 15 inches and left it for a couple hours. After reading the manual I found that I shouldn't have left it for that long. According to the manual it should hold 14-16 inches and lose no more than 1 inch over 3 minutes... which it did. So I would assume I am within specs. For giggles I put a low 5 inches of vacuum on it and left it overnight. It dropped down to maybe 2 inches.
Is it normal to not hold vacuum regardless of the pressure? Thanks in advance

 

[Scott Danforth]

you did drain all the oil prior to the test, correct?

did you also turn the input shaft and shift gears as well? while observing the pressure and vacuum? this tests the seals on the shift shaft, input shaft and output shafts

no, it should hold both pressure and vacuum. FWIW - my last test was 15 inches overnight, it still read 15 in the morning.

many times if it tests ok, it may have been the o-ring on the drain that is compromised

 

[mklearl]

Yes. I did all the above. The leak us obviously slow. The manual says use heavy oil to find the leak. How do I do that?

 

[BRICH1260]

Yes. I did all the above. The leak us obviously slow. The manual says use heavy oil to find the leak. How do I do that?

Put the unit under vacuum then take a oil squirt can and one seal at a time squirt oil onto the seals; prop shafts, there are two, inner and outer and the shift seal. Also check the three screws` O rings. A vacuum leak is harder to diagnosis than a pressure leak as you will not see any obvious signs of the leak, ie bubbles. Dont forget to rotate the shafts and gear selector.

It may take a while, but keep with it until you don't notice the drop on the gage. My leak was at the shift seal. It took me awhile to locate.

 

[mklearl]

Prop shaft seal... it goes quock when it's the first one you put oil on and you hold pressure. Thanks for the advice and help. I'm throwing in the towel on this one and I'm going to let the professionals deal with it. Too many special tools needed. With the short boating season I can't afford to not have it done right!
Thanks again

 

[bruceb58]

You replace every o-ring on every plug when you change the gear oil every year right?

 

[mklearl]

Yes. The oil that I put on the prop shaft seal dripped down to where the drain/fill plug is... so it could be either. I have the vacuum rigged up to that hole so I don't know. I did replace all o rings on the plug, vent, and dipstick before last season. I put electrical tape over the threads so the o rings wouldn't get damaged when I rolled them on. I wish it was just that but I honestly don't think so. The boat sat for 10 years so I don't think a seal going bad is out of the question.