Vented Loop - Bypass valve possible?

[CharmCityBoater]

As I re-assemble my wet exhaust on my sailboat I started to think about the vented loop for the raw water that sits between the exit of the heat exchanger and the mixing elbow. It stands to reason that even with the right elevations and precautions it is still possible to flood the engine with raw water in the event of a situation where you need to crank the engine for a long period of time, with no start. For example, to bleed the air from the fuel lines.

It seems to me that a smart idea would be to place a bypass valve on the hose that runs between the exit of the heat exchanger and the top of the vented loop so that you could re-direct raw water outboard through a above the waterline through hull temporarily rather than it going out of the regular exhaust. This would ensure there's no way to flood the engine through water leaking back into the exhaust manifold.

Am I crazy? Does such a bypass valve exist? It would need to work on 1" water hose and would require another above the waterline through-hull of course. Normally I would keep the bypass closed and only use it in the event of a long-crank situation. Am I making any sense?

Thoughts?

[deblen]

The usual way to prevent engine flooding during extended cranking is to close the raw/seawater inlet seacock.

[CharmCityBoater]

Originally Posted by deblen

The usual way to prevent engine flooding during extended cranking is to close the raw/seawater inlet seacock.

But that would mean you have an impeller that runs dry... That does not make a lot of sense to me. Damage your impeller to ensure you do not flood your engine? Sure, less of a headache but damage, nonetheless. I am an engineer and believe there is a better way to solve this. A simple T fitting on the uphill hose run between heat exchanger and top of vented loop going to a through-hull with a ball valve you could open and close seems to make more sense.

[Pete7]

Originally Posted by CharmCityBoater

But that would mean you have an impeller that runs dry... That does not make a lot of sense to me. Damage your impeller to ensure you do not flood your engine? Sure, less of a headache but damage, nonetheless. I am an engineer and believe there is a better way to solve this. A simple T fitting on the uphill hose run between heat exchanger and top of vented loop going to a through-hull with a ball valve you could open and close seems to make more sense.

There will be some water in the pump body and in addition, if you are cranking the engine its turning over quite slowly. Once it fires up a quick dash to the seacock to turn it on is all that is required.

Don't forget the "KISS" principal.

Pete

[Bowdrie]

I use a drain valve on the muffler that goes to the bilge, it's in a handy/easy to see and use location.
When the engine is going to be out of service for a long time draining the muffler also keeps water vapor from going back up the hose to the manifold/exhaust valves.
Is it foolproof?
No, like many things on a boat you need to keep your wits about you.

[LifesBetterWhenYoureBeating]

Originally Posted by deblen

The usual way to prevent engine flooding during extended cranking is to close the raw/seawater inlet seacock.[emoji2]

How would extensive cranking flood the engine? I'm not familiar with engines and it never occurred to me that could happen

When bleeding, Should I always crank the engine with the inlet seacock closed, then? Or is that only for extended cranking? How much cranking would that be?

[wholybee]

Originally Posted by CharmCityBoater

But that would mean you have an impeller that runs dry... That does not make a lot of sense to me. Damage your impeller to ensure you do not flood your engine? Sure, less of a headache but damage, nonetheless. I am an engineer and believe there is a better way to solve this. A simple T fitting on the uphill hose run between heat exchanger and top of vented loop going to a through-hull with a ball valve you could open and close seems to make more sense.

The impeller can't become dry unless you introduce air. If you close the through hull, the impeller will simply not pump the water, and it will remain filled.

[JoeRobertJr]

Originally Posted by LifesBetterWhenYoureBeating

How would extensive cranking flood the engine? I'm not familiar with engines and it never occurred to me that could happen

When bleeding, Should I always crank the engine with the inlet seacock closed, then? Or is that only for extended cranking? How much cranking would that be?

The impeller pushes raw water through the heat exchanger, through the mixing elbow, and into the muffler. While the engine is running, the exhaust gas forces the water through the muffler and out the tailpipe. If the engine is not running, the exhaust gas is not doing that. The raw water could accumulate in the muffler and then back up through the exhaust pipe into the engine.

[SailingHarmonie]

Originally Posted by LifesBetterWhenYoureBeating

How would extensive cranking flood the engine? I'm not familiar with engines and it never occurred to me that could happen

When bleeding, Should I always crank the engine with the inlet seacock closed, then? Or is that only for extended cranking? How much cranking would that be?

On a diesel, anything over 30 seconds I would consider "extended cranking." If a diesel hasn't fired in 30 Seconds, you are very unlikely to get it running just by spinning it more.

Without the actual exhaust pressure, there is nothing to blow the accumulating water out of the muffler. It builds, and builds... until it overflows back into the engine. You will not flood the engine in 30 seconds. How long it would take to actually flood an engine is highly dependent on the installation particulars.

You can either shut the seacock, or almost all waterlift mufflers have a drain plug. Pull that. Which is easier depends on your installation.

This should be something that happens like... hardly ever. If you are regularly needing to bleed your fuel lines, then something is wrong and should be fixed. In 25 years of sailing, I have had to bleed an engine 3 times? Maybe 4. No more unless I was doing something like replacing injectors or other major fuel system work.

[skipperpete]

Originally Posted by CharmCityBoater

As I re-assemble my wet exhaust on my sailboat I started to think about the vented loop for the raw water that sits between the exit of the heat exchanger and the mixing elbow. It stands to reason that even with the right elevations and precautions it is still possible to flood the engine with raw water in the event of a situation where you need to crank the engine for a long period of time, with no start. For example, to bleed the air from the fuel lines.

It seems to me that a smart idea would be to place a bypass valve on the hose that runs between the exit of the heat exchanger and the top of the vented loop so that you could re-direct raw water outboard through a above the waterline through hull temporarily rather than it going out of the regular exhaust. This would ensure there's no way to flood the engine through water leaking back into the exhaust manifold.

Am I crazy? Does such a bypass valve exist? It would need to work on 1" water hose and would require another above the waterline through-hull of course. Normally I would keep the bypass closed and only use it in the event of a long-crank situation. Am I making any sense?

Thoughts?

The only downside of your bypass idea is that, sooner or later, you will leave that valve open resulting in an overheated exhaust hose and a melted Aqualock that immobilizes your boat, far easier to simply close the raw water intake and avoid the extra plumbing although forgetting to re open the intake will result in the demise of BOTH the Aqualock and the raw water pump impeller, so that’s a problem. The start up routine should always include a look over the stern to confirm water flow out of the exhaust exit.

[CharmCityBoater]

Thanks everyone for the feedback. Looks like I was overthinking it a bit. The KISS principal makes sense. Simply either drain the exhaust or turn off water at engine through-hull.

I appreciate the feedback and wisdom.

[LifesBetterWhenYoureBeating]

Originally Posted by SailingHarmonie

On a diesel, anything over 30 seconds I would consider "extended cranking." If a diesel hasn't fired in 30 Seconds, you are very unlikely to get it running just by spinning it more.



Without the actual exhaust pressure, there is nothing to blow the accumulating water out of the muffler. It builds, and builds... until it overflows back into the engine. You will not flood the engine in 30 seconds. How long it would take to actually flood an engine is highly dependent on the installation particulars.



You can either shut the seacock, or almost all waterlift mufflers have a drain plug. Pull that. Which is easier depends on your installation.



This should be something that happens like... hardly ever. If you are regularly needing to bleed your fuel lines, then something is wrong and should be fixed. In 25 years of sailing, I have had to bleed an engine 3 times? Maybe 4. No more unless I was doing something like replacing injectors or other major fuel system work.

Thanks for the explanation!

I've only had to bleed my engine twice, both times after a fuel filter change. And both times I don't think I had to crank for more than 10 seconds. I guess I don't need to worry too much about flooding my engine, then, but I'll certainly keep this in mind

Sent from my SM-A225F using Cruisers Sailing Forum mobile app

[ColIn Ferguson]

You should not need to crank your engine to bleed the fuel system, there is a thumb lever on your lift pump.

[notoldbilbo]

I'm thinking this type may hold the solution: https://vetusonline.com/english/cata...-valve/id/372/

[notoldbilbo]

Originally Posted by ColIn Ferguson

You should not need to crank your engine to bleed the fuel system, there is a thumb lever on your lift pump.

Yes.
However, my new Beta 14 has custom Special Engine Feet; one of these blocks the manual lever, which is visible and touchable but NOT operable.

I have fitted a 'squeezy' rubber bulb ( suitable for diesel ) - as used to prime outboards - in the fuel supply line, which solves that problem.