Aeration in Water from Drive?

[BrentS]

I've been battling this overheating issue for seasons.....possibly ever since I got this SE106 in 2005. Basically everything has been replaced on my raw(salt)-water cooled 5.7, including the long block, itself.
I have a clear vinyl hose loop connected in-line between the hose from the transom assy, and the power steering cooler. Whenever I'm in gear, and going more than 1200rpm, lots of bubbles appear in the water from the drive. These bubbles are not there when in Neutral, even if revving engine up to 3000+ rpm's.
My mechanic just replaced impeller & upper housing, the entire "water pocket" assy on the upper half of drive, and the impeller pump base. I still get aeration.
Is there any suggestions?
Could this aeration somehow be from exhaust gases entering into the water stream? Could the drive have some internal casting flaw or crack???

[admin]

If your getting bubbles in the line, that must mean that it is getting air from the suction side of the pump. If there was a problem on the pressure side, then I think it would leak water instead of suck air, so I think we can rule out anything above the impeller. I know on the gen 2 style, they had issues with the pump sucking air at the gasket, but I've never heard of it on a properly installed gen 1 pump.

If there was a defect in the case, it would have to be in the exhaust cavity below the waterpump, and it would have to let exhaust gases make it to the water passage that goes from the plastic water intakes up to the pump base. It's possible, but I would suspect you should see something if you look down the cavity with a flashlight.

My last idea would be if there is something on the boat that is disrupting the flow of water to the drive. It's a stretch, but inspect the area below the gimbal housing to see if anything is below the hull.

I hope this helps. If I think of anything else I'll let you know.

Tech Support

[BrentS]

Thanks for the response.
When the boat was hauled to replace all the aforementioned drive components, there was nothing on the hull. There is a thru-hull transducer 3 ft forward of transom, but it only sticks down 3/16" and is flat/smoothe.
Plus, even at only 1200 rpm's (in gear) the bubbles appear, and at that point the hull speed is only a few mph.
Your response is consistant of what I was thinking.
Unfortunately, when mechanic had drive apart, he didn't look closely in any cavity. He found the impeller was loose around the brass hub, and logically assumed that was the problem (spun impeller). However, with all the new parts, air bubbles and temp were exactly the same.

[BrentS]

I was thinking of obtaining a used lower half, to trouble shoot this problem. Does that sound like a good idea?
The lower half of the drive should be in question, if we're suspecting some kind of issue with the suction side of the pump, correct?
Any Alpha lower half should work? Gear ratio (i.e. 1.5, 1.84, etc.) is only in the top half?

[admin]

That is correct, any lower will work.

Tech Support

[Bt Doctur]

Have your mechanic drop the lower and apply muffs to it. Betting you`ll find a leak at the water pump base section.
still or slow the water pump housing is covered in water, at higher speed the water pump is exposed to waste water and hot exaust. a suction side will draw air not water, theres your bubbles.

[BrentS]

So, if we drop the lower half, plug the gear oil hole (to prevent any water from getting in), apply muffs to the side intake passages; should we expect some water to come out the copper discharge tube from leaking through the internal impeller/housing cavity?
Should that be the only place the water may come out? Or, what about from the shaft area....the slinger???

I just don't know why the base would leak, if the entire base assembly was just replaced...
My mechanic even gave me all the old parts (base, impeller, upper housing, etc.).

[Bt Doctur]

no water should appear anywhere. not the slinger, copper tube or base.water does not normally come out the top of the pump, it must be pumped out. will not show water on muffs. I`m betting there is a bad gasket or warped base allowing hot exaust to be sucked in. easiest way to check is using muffs. leakage will be readily apparent. I have had 2 leaking bases already, 1 sierra and 1 merc oem.
Since then, when I`m replacing a pump I check with muffs before I put it to the upper.

[BrentS]

Update:
This aeration problem was definitely in the drive. My mechanic replaced my SE106 with a used Merc drive, and as soon as I got the boat up on plane, I could tell it was fine. While the idle temp was a little higher than the SE106, the temp barely rose any upon getting to cruising speed, and even at WOT.
Does Sterndrive Engineering want to address this issue at all?

[admin]

Did you replace just the lower, or the complete? Do you see any issue with the case below the water pump?

Tech Support

[BrentS]

We replaced the entire unit. I haven't had any chance to inspect the unit. As one can imagine, this issue has cost me so much money and so many hours; I don't know if I want to invest much more on this unit.
One would not expect to have an issue after replacing the impeller, upper housing, pump base, and water pocket assy in a drive.

Did you replace just the lower, or the complete? Do you see any issue with the case below the water pump?

Tech Support

[Bt Doctur]

Did you check the lower with the muffs in my earlier post before replacing the unit?

[admin]

The unit is about 6 years out of warranty, however if there is a flaw in the case, we would be able to take care of it.

Tech Support