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Old 29-07-2021, 10:38   #1
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Poorly designed/built anti-siphon?

I recently took ownership of a 1978 Columbia 10.7 with a Yanmar 2qm20 engine. I'm not all that experienced with marine diesel, but I get the feeling that the anti-siphon setup on this boat was designed to fail.


Photo for reference (pardon the poor MS Paint level markup):



As far as I can tell this is intended to be an anti-siphon setup, with the nice exhaust-rated tubing passing from the heat exchanger to the exhaust. Unfortunately, the "anti-siphon" outlet (circled) of this setup is just connected to some basic small diameter (TPE?) tubing which I highly doubt is rated to carry hot salt water and/or exhaust gasses. It seems that this tubing is reaching the end of its life, as it consistently cracks near the hose clamp, resulting in a nice spray of salt water right over my engine.


I've done some temporary repairs a few times now by cutting back past the cracks, re-attaching the hose over the barbs, and re-connecting the hose clamp, but I still get more cracks eventually. I'd like to fix this system properly and I'm looking for some advice. Should I keep everything as-is and just replace the plastic tubing? I can't imagine that tubing is really rated for this kind of workload. Ideally I'd like to replace it with proper exhaust rated tubing, but I'm not sure if that would cause other issues (I'd also have to work out how exactly to send that overboard, as the current setup is designed around this smaller diameter tubing).

I know some work was done on the engine at some point to install a heat exchanger, as the boat originally just cooled with salt water directly. I'm not sure if this anti-siphon setup was installed then or if it is original to the boat.


Any suggestions for fixing this properly would be appreciated!
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Old 29-07-2021, 11:45   #2
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Re: Poorly designed/built anti-siphon?

I can't see a good way to edit the post. I've done some more research and found that using this kind of tubing for an anti-siphon setup apparently isn't that uncommon (https://www.cruisersforum.com/forums...em-234903.html). I think perhaps my tubing is just old, so I'll try just replacing it and cross my fingers. However, if people have some other more sustainable solutions I'd be interested!
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Old 29-07-2021, 13:08   #3
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Re: Poorly designed/built anti-siphon?

I'd just replace the vent tubing (and the rusted conduit clamps). You can use a silicone hose or other high-temp resistant material if you like. Normally, the vent hose is only subjected to warm seawater so it's really not a high temp situation.


You do want to make sure to use a reinforced hose that will not collapse when subjected to a vacuum. The plastic tube in the pictures looks sketchy in this regard.
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Old 29-07-2021, 21:01   #4
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Re: Poorly designed/built anti-siphon?

I would try fuel hose if the larger O.D. is ok as thats easy to get & pretty tough.
I use it for hot engine oil lines on our Yanmar ysm8 & they have survived a few years so far. Think they'd be fine in your application.


just curious emusan but why did the P.O. covert it to fresh water cooling & did he notice any difference after doing so? Appreciate you may not know.
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Old 29-07-2021, 22:02   #5
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Re: Poorly designed/built anti-siphon?

Thanks for the input!


I don't think a larger O.D. would be an issue, the tube doesn't pass through any narrow spaces so I should be fine. I picked up some reinforced tubing intended for water lines (but not engine cooling water) today for a temporary fix, I'll see if I can get something better suited to it tomorrow.


The fresh water cooling conversion was two owners prior, so I'm not entirely certain why it was done, but the boat has been in salt water its whole life, so I assume it was to extend the life of the engine.
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Old 29-07-2021, 23:46   #6
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Re: Poorly designed/built anti-siphon?

As others have said, the small tube will only have warm seawater in it, never exhaust and should never be under vacuum, the smaller the better as it is really only there to allow air to enter when the water flow stops. Way better than small duckbill valves found on most commercial products.
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Old 30-07-2021, 01:03   #7
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Re: Poorly designed/built anti-siphon?

Welcome aboard CF, emusasn. Congratulations on having a 2QM20, IMHO they are the best engine Yanmar ever produced. Solid, overbuilt, will last a lifetime and the wearable parts (bearings/rings/pistons/sleeves/valves etc) are all still available if perchance you manage to get many many thousands of hours on the clock. Well maybe the big brother (3QM30) is technically slightly better.

Others have answered your question but I have two for you although I appreciate you may not be able to answer them.

Did the coolant cooling conversion use the Yanmar block mounted coolant pump or something else?
Was the thermostat changed from the original cooler raw water one to allow for higher running temperatures?
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Old 30-07-2021, 01:29   #8
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Re: Poorly designed/built anti-siphon?

Quote:
Originally Posted by emusan View Post
I recently took ownership of a 1978 Columbia 10.7 with a Yanmar 2qm20 engine. I'm not all that experienced with marine diesel, but I get the feeling that the anti-siphon setup on this boat was designed to fail.


Photo for reference (pardon the poor MS Paint level markup):



As far as I can tell this is intended to be an anti-siphon setup, with the nice exhaust-rated tubing passing from the heat exchanger to the exhaust. Unfortunately, the "anti-siphon" outlet (circled) of this setup is just connected to some basic small diameter (TPE?) tubing which I highly doubt is rated to carry hot salt water and/or exhaust gasses. It seems that this tubing is reaching the end of its life, as it consistently cracks near the hose clamp, resulting in a nice spray of salt water right over my engine.


I've done some temporary repairs a few times now by cutting back past the cracks, re-attaching the hose over the barbs, and re-connecting the hose clamp, but I still get more cracks eventually. I'd like to fix this system properly and I'm looking for some advice. Should I keep everything as-is and just replace the plastic tubing? I can't imagine that tubing is really rated for this kind of workload. Ideally I'd like to replace it with proper exhaust rated tubing, but I'm not sure if that would cause other issues (I'd also have to work out how exactly to send that overboard, as the current setup is designed around this smaller diameter tubing).

I know some work was done on the engine at some point to install a heat exchanger, as the boat originally just cooled with salt water directly. I'm not sure if this anti-siphon setup was installed then or if it is original to the boat.


Any suggestions for fixing this properly would be appreciated!
i think raw water flow opposite what you sign. seacook to raw water pump heat exschanger

exchange bronze to pvc

https://www.vetus.com/en/exhaust-systems/air-vents.html
how must look here

https://www.vetus.com/en/exhaust-systems.html
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Old 30-07-2021, 02:18   #9
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Re: Poorly designed/built anti-siphon?

Quote:
Originally Posted by more View Post
i think raw water flow opposite what you sign. seacook to raw water pump heat exschanger

exchange bronze to pvc

https://www.vetus.com/en/exhaust-systems/air-vents.html
how must look here

https://www.vetus.com/en/exhaust-systems.html
Now I am curious, just how do you arrive at this concusion from the information supplied.??
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Old 30-07-2021, 23:24   #10
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Re: Poorly designed/built anti-siphon?

Quote:
Originally Posted by more View Post
i think raw water flow opposite what you sign. seacook to raw water pump heat exschanger

exchange bronze to pvc

https://www.vetus.com/en/exhaust-systems/air-vents.html
how must look here

https://www.vetus.com/en/exhaust-systems.html

And just where would the water go after the " seacook to raw water pump heat exschanger", I know , through the vented loop and then to the exhaust, just as the op has indicated.
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Old 15-09-2021, 16:33   #11
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Re: Poorly designed/built anti-siphon?

I know it has been awhile since this thread had any activity, but I wanted to answer the last few questions and provide a quick update in case it might help anyone out there with a similar issue.


I ended up going with just the reinforced tubing intended for warm freshwater. At the very least it seems a lot more robust than the material that was in place from the previous install, so I'm hoping it lasts. Right now I just have the tubing exiting into the cockpit through a "handle" gap in the port side lazarette. Not ideal for any kind of permanent install, but it seems to be working well so far. Any water that comes out just drains through a cockpit drain, which also forces me to keep up with cleaning them!


The previous line emptied overboard by tapping into one of the cockpit drain lines below deck. Initially I thought this was done with a T-split and proper fittings, but on closer inspection it looks like the anti-siphon line was just shoved into the tubing and glued in place, meaning that replacing it isn't really a great option. I'm still researching how best to go about removing that tubing and getting my new anti-siphon line installed better, but for now it's not a high priority (I feel like I'll end up having to replace all of this anyway).


To answer the few questions that came up:



Quote:
Did the coolant cooling conversion use the Yanmar block mounted coolant pump or something else?

The conversion uses a Jabsco pump. I'm not sure the exact model offhand but I can look it up if needed.


Quote:
Was the thermostat changed from the original cooler raw water one to allow for higher running temperatures?

Unfortunately I'm not really sure, though I've found that the engine seems to run pretty cool in general (it helps that I'm in north Pacific waters that are already quite cool I'm sure). The maximum temperature I've seen is right around 150 F, assuming that my gauges are correct.


Quote:
i think raw water flow opposite what you sign. seacook to raw water pump heat exschanger

I'm pretty sure I traced it out pretty closely and the flow is as I described. Is there a particular reason you recommend swapping from bronze to PVC? Just to be clear, in this case I'm not really seeing any direct issue with the bronze parts themselves, the main issue is with the anti-siphon tubing that was installed previously.


Thank you to everyone here for your input and help!
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