Air Lock in raw water system downstream of pump

[boatbod]

Glad you fixed it. As an aside, it's not always the cover plate. I have seen pump housings so worn that even a new cover plate doesn't make it work any better.

[JOHNMARDALL]

Glad to hear that you've solved the problem, but I agree with one of the previous posters that the location of your vented loop/anti/siphonage valve doesn't seem to be right. The purpose of the anti-siphonage valve is to stop water siphoning through the raw water system when the engine is not running, with the risk that if left long enough, drip by drip, it will fill up the waterlock and back up into the exhaust manifold, then through an open exhaust valve and into a cylinder. On the next engine start, the piston hits a plug of incompressible water, and unless you're very lucky and it just stops the engine, massive damage is done to the piston, connecting rod, cylinder head, etc. Then there's the internal corrosion.

The conventional location of the vented loop is between the seawater discharge of the heat exchanger and the exhaust mixing elbow.

If you'd like to send me a sketch or some photographs, I might be able to understand your system better. Sadly, I've had to console and service a few customers whose installers either left our the vent completely (common) or put it in the wrong place (very rare).

Best Regards

John Mardall
Vetus Maxwell Group

[gpeacock]

Originally Posted by JOHNMARDALL

...If you'd like to send me a sketch or some photographs, I might be able to understand your system better. Sadly, I've had to console and service a few customers whose installers either left our the vent completely (common) or put it in the wrong place (very rare).

Best Regards

John Mardall
Vetus Maxwell Group

Hey John, I'll never pass up free advice.
Here is the cooling system schematic

Which I got from this link: Cooling system schematic
#1 is the heat exchanger, #2 is the oil cooler and #5 is the exhaust manifold/injection elbow.
You can see a u shaped pipe running from the oil cooler to the heat exchanger. Its labeled #13. I have the vented loop installed there instead of the small pipe.
One of the blowups in that schematic shows a pipe labeled as 23 which goes from the heat exchanger to the exhaust elbow. You can see the takeoff and return for the gear oil cooler. Given that setup, I can understand why they plumbed the vent where they did. The loop was an option and creating a cheaper drop in replacement for pipe #23 that included the loop would have been a challenge.
My very basic understanding of vented loops says that as long as its after the pump but before the exhaust elbow it will do its job. Am I wrong? This engine is from 1985 so maybe conventional thinking has changed since then, having said that this boat has been around the world once and hasn't managed to hydrolock yet. Unless I decide to put in a forward facing scoop thru-hul or a dripless shaft seal I dont see that happening in the future.(Im knocking on wood)
Thanks again
Gary

[JOHNMARDALL]

Originally Posted by gpeacock

Hey John, I'll never pass up free advice.
Here is the cooling system schematic

Which I got from this link: Cooling system schematic
#1 is the heat exchanger, #2 is the oil cooler and #5 is the exhaust manifold/injection elbow.
You can see a u shaped pipe running from the oil cooler to the heat exchanger. Its labeled #13. I have the vented loop installed there instead of the small pipe.
One of the blowups in that schematic shows a pipe labeled as 23 which goes from the heat exchanger to the exhaust elbow. You can see the takeoff and return for the gear oil cooler. Given that setup, I can understand why they plumbed the vent where they did. The loop was an option and creating a cheaper drop in replacement for pipe #23 that included the loop would have been a challenge.
My very basic understanding of vented loops says that as long as its after the pump but before the exhaust elbow it will do its job. Am I wrong? This engine is from 1985 so maybe conventional thinking has changed since then, having said that this boat has been around the world once and hasn't managed to hydrolock yet. Unless I decide to put in a forward facing scoop thru-hul or a dripless shaft seal I dont see that happening in the future.(Im knocking on wood)
Thanks again
Gary

Hello Gary,

Thanks for the information, which has set me thinking. I guess that as long as the vented loop is well above the heeled waterline (close to centerline of boat) it will work, and that the seawater content of the heat exchanger, which will drain down into the waterlock, will not be enough to fill the waterlock. Certainly your many miles of sailing without an engine flooding event support that. Please tell me what you are thinking about with the scoop and dripless seal comment - I too seek ideas, information and education

[boatbod]

Conventional wisdom is to install the vented loop between the heat exchanger discharge and the exhaust elbow inlet. This minimizes water drain down and gives maximum room in the muffler for exhaust water draining back.

[Sailmonkey]

Originally Posted by boatbod

Conventional wisdom is to install the vented loop between the heat exchanger discharge and the exhaust elbow inlet. This minimizes water drain down and gives maximum room in the muffler for exhaust water draining back.

Who cares where it is so long as it breaks a siphon?

[boatbod]

Originally Posted by Sailmonkey

Who cares where it is so long as it breaks a siphon?

The volume of water that drains back into the muffler pot is important, but hey, who cares about that as long as the siphon is broken.

[Seman]

If your salt water filter is below the waterline, install a breezer , drill a small hole in the filter housing, fit a small hose connector and run the hose at least 3 feet above the waterline. The air will escape and even a worn impeller or worn pump housing will not stop water cooling your motor. I have done it on my 2 filters after getting tired of replacing slightly worn impellers or scarred pump housing. Never had a problem again.

[gpeacock]

Originally Posted by JOHNMARDALL

Hello Gary,

Thanks for the information, which has set me thinking. I guess that as long as the vented loop is well above the heeled waterline (close to centerline of boat) it will work, and that the seawater content of the heat exchanger, which will drain down into the waterlock, will not be enough to fill the waterlock. Certainly your many miles of sailing without an engine flooding event support that. Please tell me what you are thinking about with the scoop and dripless seal comment - I too seek ideas, information and education

Just to be clear... the boat has been around the world... not me... yet.
Those comments were a bit tongue and cheek. The scoop was an idea I considered to solve the airlock issue until I did the research and discovered that while sailing it would probably force water through the engine, into the water muffler and then back up into the engine. I quickly crossed that option off my list.
As for the drip-less shaft comment. This year I've been in anchorages with 2 separate boats who have come in with hydro-locked engines due to the drip-less shaft seals. One was a cat who had both engines hydrolock. I have no idea if they were installed properly or not but that combined with another friend who almost sank because of a hose clamp breaking on his drip-less has crossed that option off my list as well. I'll stick with the 4 drips a minute while motoring.
Thanks
Gary

[gpeacock]

Originally Posted by Seman

If your salt water filter is below the waterline, install a breezer , drill a small hole in the filter housing, fit a small hose connector and run the hose at least 3 feet above the waterline. The air will escape and even a worn impeller or worn pump housing will not stop water cooling your motor. I have done it on my 2 filters after getting tired of replacing slightly worn impellers or scarred pump housing. Never had a problem again.

Interesting idea. Similar to a vented loop before the pump... I wouldn't drill a hole in my strainer but I could put a t fitting just after the strainer.. To bad I've put the pump back in. It would have been fun to experiment with that when I had the test jig set up. Its something I will consider if my problem isn't solved.
Thanks
Gary

[JOHNMARDALL]

Originally Posted by gpeacock

Just to be clear... the boat has been around the world... not me... yet.
Those comments were a bit tongue and cheek. The scoop was an idea I considered to solve the airlock issue until I did the research and discovered that while sailing it would probably force water through the engine, into the water muffler and then back up into the engine. I quickly crossed that option off my list.
As for the drip-less shaft comment. This year I've been in anchorages with 2 separate boats who have come in with hydro-locked engines due to the drip-less shaft seals. One was a cat who had both engines hydrolock. I have no idea if they were installed properly or not but that combined with another friend who almost sank because of a hose clamp breaking on his drip-less has crossed that option off my list as well. I'll stick with the 4 drips a minute while motoring.
Thanks
Gary

Thanks Gary,

As a generality, I'd say that the further upstream the vented loop is from the mixing elbow, the more water will siphon back into the waterlock when the engine is not running. With a tight system and a new impeller in the seawater pump, not much water can get through, but as the impeller wears, the rate of flow (but not the volume) can be expected to increase. It's important to check the vented loop as routine maintenance. Some models have spring loaded valves which can become salt encrusted and stuck. Things that don't require much maintenance tend to get no maintenance.

I take your point on the direction of the intake scoop, but don't understand how a dripless seal would contribute to siphonage and engine flooding. Would you expand on that please? (Full disclosure: I have a PYI dripless seal on my own boat).

Best Regards

John Mardall
Vetus Maxwell Group

[gpeacock]

Originally Posted by JOHNMARDALL

I take your point on the direction of the intake scoop, but don't understand how a dripless seal would contribute to siphonage and engine flooding. Would you expand on that please? (Full disclosure: I have a PYI dripless seal on my own boat).

Best Regards

John Mardall
Vetus Maxwell Group

I dont have any more information on the hydrolock events. It sounded like both boats somehow had their shaft seals plumbed into either their vented loops or raw water intake. I don't know if this is common practice or not. In any case both boats sailed in large following seas with the engines off and when they went to start them... kablam. I also don't know how they knew it was the shaft seals but in both cases they were positive that was the cause. The main reason I made the comment is because I encountered both boats within a week of each other and then 2 weeks later my friend had a hose clamp go on his which almost cost him his boat. They were probably all attributed back to installer or owner error but even so, us humans are only so smart. Simpler is better.

[Seman]

Originally Posted by Seman

If your salt water filter is below the waterline, install a breezer , drill a small hole in the filter housing, fit a small hose connector and run the hose at least 3 feet above the waterline. The air will escape and even a worn impeller or worn pump housing will not stop water cooling your motor. I have done it on my 2 filters after getting tired of replacing slightly worn impellers or scarred pump housing. Never had a problem again.

Unfortunately this was only a temporary fix. A year later same problem again.
After removing the pump and cleaning it up I noticed the pump lid had a groove worn in it and also on the other side the bronze pump body had what looked like corrosion eating into the material.
That's why the pump wasn't sucking properly.
I filled both, the worn groove in the lid and the damage in the pump body with JB Weld Steel and sanded it flat. No more problems for a couple of month!
Will report back if this was only another temp. fix .

[Andina Marie]

We had this problem with our watermaker. While underway small bubbles would be sucked in, go through the raw water pump and get trapped in the filter of the watermaker.

Here is what we used to clear the air lock. It does require cutting off the raw water for about 20 seconds to let the air out and then continue,otherwise it is automatic.

See http://BUBBLE EXTRACTOR

[Seman]

Originally Posted by Seman

Unfortunately this was only a temporary fix. A year later same problem again.
After removing the pump and cleaning it up I noticed the pump lid had a groove worn in it and also on the other side of the impeller the bronze pump body had what looked like corrosion eating into the material.
That's why the pump wasn't sucking properly.
I filled both, the worn groove in the lid and the damage in the pump body with JB Weld Steel and sanded it flat. No more problems for a couple of month!
Will report back if this was only another temp. fix .

Another only part success. The lid is worn again, JB Weld partially peeled off.
This time I sanded the lid until flat. The pump body repair appears to be still ok.
Will report back if body repair failed.