Raw Water Clear tube test - yield lots of air bubbles

[jtm3]

DP SM 1.78 with TSK SX MHP Transom shield (2001) - replaced risers and manifolds in Nov, this spring among other things replaced bellows (both) and shift cable. On muffs and in water at idle temp is fine, then under load at about 2500 rpm - temp starts to rapidly climb. Checked raw water pump (volume test good), checked lines for blockage - everything clear. Installed clear tubing on suction line up to T-Stat housing and legs feeding manifolds - sure enough as the boat is put under load - starts sucking air, lots of bubbles. Also, at dock increasing RPM and changing trim, yields bubbles which might hint at the hose connection.

Have pulled the boat and going to drop the outdrive this week. I have searched the forum and I think someone said that the tube to outdrive connection is the likely culprit. I'm working with a very experienced mechanic - most of his experience is with Merc's and old OMC's. So hoping the brain trust can help point us to steps to ID the source of the air leak. Should we just swap out the nipple or are there other tricks or ideas which should consider?

Thanks in advance - go easy on me, just trying to learn as much as I can.

 

[GeorgeDes]

Yes, the hose between your outdrive and the intake of the raw water is the first place I would check. Either a lose connection or a small leak. Appears it would be somewhere inside the bilge area since it is pulling in air.

 

[SD2600]

My guess is your outdrive is the culprit... looks up the schematic on your drive... follow the vent holes on the lower and inspect/replace all parts that lead to the fitting through your transom... the rubber fittings don’t last forever and the smallest defect will cause air to be drawn in while on plane...also u might want to liberally coat all gaskets with tripe guard.... I chased this exact problem on my sx-m... good luck, take pics and keep us posted

 

[jtm3]

Thanks SD2600. Getting discouraged we backfilled the suction line and only see water at the nipple which appears has a drain hole in it. We have spent a lot time researching and checking fittings and hoses. Would like to find where the air leak is and not just throw parts at it.

The overheat diagnoses manual says if you find air entering it must be fixed....we know that part, sure would like a few more ideas. If anyone has any, we are all ears.

 

[SD2600]

Really inspect the plastic fitting that has the small weep hole in it... what does the housing look like that it sits in.... if the housing is not pristine this will allow air in.... trust me I know the feeling.... I ended up replacing every hose and fitting from my impeller to the rubber fitting in the lower unit.. I still had an air leak on plane... pulled the drive and the housing wasn’t pristine.... ended up epoxying that mating surface and problem solved

 

[jtm3]

Thanks SD2600 - Classic no good deed goes unpunished - trying to take care of differed maintnance and end up creating a problem somewhere else. What you are saying matches with what others have said, that location is often the trouble spot. One guy wants me to switch to thru-hull pick up. Not sure I'm ready to go that route just yet! Thanks again!

 

[dypcdiver]

Sometimes the raw water pump seal can be sucking air, is the clear hose before or after the pump?

Noticed that you say on the suction line to "T" stat that is pressurised. Put a clear hose on the suction side of the raw water pump, to eliminate the pump seal.

 

[jtm3]

So just to close this out in the end we discovered that is was located at the nipple (as folks suggested was the likely culprit) - what it appears to be was the nipple was missing the gasket (20). We never touched the nipple and what we can't really understanding is why it wasn't sucking air last year.... (the nipple has a weep hole that gets covered by gasket) Took it out today, under load, up on a plane - no air in the clear hoses, no temp spike - thankfully!

The nipple appears to be have changed by a previous owner.....who knows how it wasn't sucking air in the past...


Thanks again for everyone's help!

 

[SD2600]

Good to hear! Common culprit... enjoy

 

[dypcdiver]

I belive the small hole in the nipple is to allow water to drain so that there is no water trapped to freeze in the winter.

 

[Lubak572]

How hard is it to change that nipple? Does number 11 above have to come off. I already have my drives off?

 

[jtm3]

Lubak572 - #11 does not have to come off - we were able to reach everything with just the drive off.

dypcdiver - that is what we thought as well, but the weep hole is right were the gasket sits and was the source of the air, once the gasket went in the notch it blocks the weep hole and inturn blocks it from pulling air.



Fingers crossed for a trouble free summer during our all too short season!

Thanks again for all the help!

 

[Fishhead-1]

I just pulled mine out today, you can see the o ring in the first groove. There isn't anything in the groove that has the weep hole in it.

 

[dypcdiver]

The manual says that the "O" ring goes in the groove without the hole.

 

[Lou C]

OK this is part of the original OMC Cobra design and the changes that were made during the joint venture era with Volvo may have made this problem more likely to happen. From your diagram, on the Cobra up to '93, there was a paper gasket between the pivot housing that covered that o ring gasket #24 in the pivot housing. You were supposed to coat this gasket on both sides with OMC gasket sealer. If the sealing surface of the pivot where the o ring fits, or the upper gear housing that abuts up against it wasn't perfect, the paper gasket would for sure seal it. I never had trouble with air getting sucked in on the orignal Cobra. Now when it was redesigned to create the Volvo SX and the last of the OMC Cobras (1994) that gasket was eliminated. That means that the o ring part 24 in the pic above is the only thing that seals that area. And, if the groove in the pivot or the mating surface of the drive that abuts it is not in good shape, it might not seal. I would in the future coat that o ring in OMC/Evinrude triple guard grease, both in the groove and on the drive surface, it helps hold the o ring in place too.

About the nipple, the O ring does NOT go in the groove with the hole! In my OMC shop manual it shows that the o ring goes in the groove closest to the square section. If it was in the groove with the hole, the water drain would likely not work. It says "do not put the oring in the drain hole groove, this would prevent water draining out during winterization and could result in freeze damage"

the drain hole is supposed to face down. when re-assembling you could use sealer on the oring on the nipple where it fits in the pivot housing. When you remove the plug on the side of the pivot housing, it is supposed to drain water in the hose from the transom mount to the drive. I heard that in later years Volvo eliminated that drain plug, maybe the Volvo does not hold water in this hose like the OMC did due to the difference in the impeller location.

So when you do an R+R on the Volvo SX drive, make sure that O ring part #24 above is in that groove, I'd coat it and the part of the drive that mates up to the pivot housing with OMC triple guard. It also prevents the drive from getting corroded to the pivot housing due to the lack of a gasket to prevent corrosion.

 

[Fishhead-1]

Ok thanks Lou , that makes sense so the cobra the housing was drilled and had a plug to drain, then the penta housing wasn't drilled but still used the same nipple. that clears it up