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petdoc4u 10-22-2016 05:31 PM

Perplexed, help needed
This is a topic that I posted once before concerning salt water exiting an overflow vent only when the engine is running at 1000 RPM or above. This issue has remained unresolved, however I now have more information. The salt water flows to the overflow vent through 5/8" clear reinforced tubing. This tube at its origin is connected to the vent fitting on the top of a vented loop. There are two hoses attached to the vented loop. One hose comes from the outflow side of the transmission oil cooler through which salt water flows to the vented loop and the other hose carries that salt water to a fitting on the exhaust elbow. There is another hose which carries salt water from this common exhaust fitting to the shaft seal. The engine does not overheat and the flow of water from the vent is not damaging. We have owned the boat 6 years and this became an issue last year. I am concerned that this could lead to a more serious problem of some sort. It would seem that water is backing up in the vented loop causing pressure which is venting the water through the overflow. Also, when I squeezed the hoses going to/from the vented loop the hose coming from the transmission oil cooler had a slight crunch to it close to its origin. I have no idea if that is significant. Please share your ideas as they are always much appreciated.

psneeld 10-22-2016 05:58 PM

Sounds like my new setup and pretty normal.

If something has changed and your hoses sound crunchy.

Replace those hoses and see what happens...maybe they are restricted because of sslt...but I doubt it.More likely they are old and delaminating?

MYMT 10-22-2016 06:40 PM

Sounds to me like the vented loop is leaking, allowing water to go out probably only until the pressure becomes great enough with higher rpm's. The loop should only let let air in when the engine and associated pressure is off, it should not allow water out while its under pressure. Replace the vented loop or just the valve on top if you can and that should solve the problem.

petdoc4u 10-22-2016 08:12 PM

Thank you for your replies. Once I became aware that the vented loop could be the problem I rejoiced that the builder was forward thinking enough to have run a hose from the vent on the loop to an overflow vent thus eliminating the possibility of that salt water doing damage within the boat. After reading additional posts I decided to re-route the vent hose overboard to an area where the salt water discharge will not leave stains on the fiberglass. I hope I'm not missing anything.

MYMT 10-22-2016 09:24 PM

if the vented loop is leaking, it will diminish the amount of cooling water introduced to the shaft seal, (in my case the packing gland and cutlass bearing), as the vented loop is not designed in the system to leak, only to eliminate a siphon back into the manifold. Probably wouldn't make a huge difference as some boats don't have water injected there anyway, but I'm not sure. The engine won't overheat, but possibly the area that you describe as a 'shaft seal' may not cool as designed...

LarryM 10-22-2016 10:06 PM

Vented loops generally have a fitting containing a rubber duckbill valve. It blocks water from discharging while running, but allows air to enter when the engine stops to break any vacuum that could lead to engine flooding. In the event the duckbill becomes clogged, a vacuum and resulting siphon can occur. If, on the other hand, the duckbill leaks, it will behave exactly as you are observing.

These are easy to check or replace if accessible. :thumb:

DavidM 10-23-2016 06:30 AM

If your engine elevation requires a vented loop, there are two ways to install them: with a continuous vent and with a check valve. Most sailboats have a check valve which if clean and working right doesn't let any sea water out, jut air in.

But yours is a continuous vent. The fitting at the top of the loop doesn't have a check valve in it. So when the engine rpm gets above 1,000 it generates enough flow to fill the loop and sea water flows from the vent.

Usually these vents are routed overboard. I didn't quite understand where yours was routed and why you rerouted it. I also wonder about the prop shaft gland flush water. Is this coming from the vent or the main flow path. It would be better if it were from the main path so it could get water at low rpms.

So, in summary the system sounds like it is operating as designed as others have noted. The "crunch" inside the hoses is a little disconcerting. Pull it off and look inside, it may be fouled with scale or the reinforcing wires may be corroded. Replace it.


psneeld 10-23-2016 06:48 AM

1 Attachment(s)
The hole in the "vented loop" is small enough there should be no concern for water flow to the shaft or exhaust.

The hole in the overboard discharge that comes with the Vetus package is something like a 1/4 inch.

This is from the other exhaust loop thread....

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