WATER SIPHONING INTO RESONATOR - ALMOST RESOLVED

[mejim707]

This is a specific issue for a specific problem and please consider this as a question for a specific issue and please don't move / merge / delete this post.

I've identified an issue where starting on water was impossible because water was actively pouring into the exhaust due to a siphoning effect after running the boat for a while. After comments and suggestions I tied the inlet hoses in a high loop to break the siphon. This has mostly resolved the issue.

However, it seems that the issue is still happening occasionally. Even though I have the hoses tied in a high loop. the siphoning is still occurring rarely and I hear water pouring into the resonator. Most of the time it's fine, but you know that one time it happens and I don't check I will be on a far away dock and I'll be stranded. For now, I will have no choice but to clamp off the hoses every time I stop the boat to 100% ensure the water stops siphoning in.

The question is, why when you shut the engine off does the engine allow the water to continue pouring / siphoning in? How could this happen with my engine and boat and doesn't seem to be happening for others. I've seen many pictures of peoples engine bays for these boats and I've only seen 1 where the hose is long enough and it looks like the inlet hose from the jet pump is tied in a high loop.

Something is causing the water to continue flowing even though the engine is off. Something that I don't know of is causing a suction affect the continues to draw in water until I physically break the siphon by clamping the water hoses.

I'm reaching out to the pros here since you all know these engines on a level that you may know why this endless loop would happen, only after running for a while then shutting the engine off.

I mean I could add more hose and elevate that 10 feet above the boat to make sure this never happens again but I don't think I should have to keep elevating this high loop even higher when there must be something else at work here.

Thank you in advance!

 

[Spider4real]

First off, I don't have the knowledge or expertise to be of to much help. All I know is my challenger had all the cooling lines flat on the bottom of the engine compartment. I never had to tie anything up so even though this has helped your issue, i do not think it is the root cause.

Looking back at previous pictures you took I noticed the resonator was much darker purple than the muffler. This leads me to believe it is running too hot and cooked the paint. Or at least it was at one time. Maybe the hot resonator is what is drawing in the water. Maybe it not getting enough water when it's running.

 

[mejim707]

First off, I don't have the knowledge or expertise to be of to much help. All I know is my challenger had all the cooling lines flat on the bottom of the engine compartment. I never had to tie anything up so even though this has helped your issue, i do not think it is the root cause.

Looking back at previous pictures you took I noticed the resonator was much darker purple than the muffler. This leads me to believe it is running too hot and cooked the paint. Or at least it was at one time. Maybe the hot resonator is what is drawing in the water. Maybe it not getting enough water when it's running.

Thank for the reply! Actually, that color difference was me at an attempt to paint it because it was old and crusty looking lol

But I do know the resonator, full exhaust and engine head all stay cool to the touch when running and when off. It's never hot where I can't touch it no matter how hard I drive the boat.

But that's very interesting, you have the lines on the hull like me, and didn't have this issue. So for some reason the engine or something is creating a suction effect when it shouldn't. This is baffling.

 

[mejim707]

Update: Yesterday I flushed the engine. I left the engine compartment open during this. When I shut the hose off, then shut off the engine, I could hear water pouring into the resonator.

Mind you, the hose was not connected, and I was not in water. So the water was pouring into the resonator from the engine.

The engine has a drain at the bottom, under the tuned pipe. That's where water is ejected into the tail pipe of the exhaust. That seems to be working properly while running since I see water coming out of that.

But, should the water from the engine dump into the resonator when the engine is tured off? It may be that I've fixed the siphoning effect, however, the sound I now hear is from the remaining water through the engine being drained into the resonator through the water valve. I know it's from the water valve because if I clamp the large hose going to the water valve, the sound stop.

I think we're getting close to identifying the root cause. But I really need this community and the experts advice.

What are your thoughts on why the engine is dumping its remaining water into the resonator? This can and will cause the resonator to fill and prevent the engine from starting since the exhaust is full of water.

Thank you!!

 

[Spider4real]

Water will always pour back into the resonator. Gravity kinda guarantees this. I'm having a hard time believing that there is enough water that will flow back and fill the resonator to the point it is blocked. Most water will be trapped in the water pockets in the engine. Some from the hoses will go back into the water regulator and the resonator. It should not be that much. Have you ever verified how much water is in there after you stop it? Have you ever disconnected the hose that connects the resonator to the tuned pipe and see what comes out and how much?

 

[mejim707]

Water will always pour back into the resonator. Gravity kinda guarantees this. I'm having a hard time believing that there is enough water that will flow back and fill the resonator to the point it is blocked. Most water will be trapped in the water pockets in the engine. Some from the hoses will go back into the water regulator and the resonator. It should not be that much. Have you ever verified how much water is in there after you stop it? Have you ever disconnected the hose that connects the resonator to the tuned pipe and see what comes out and how much?

Hi thank you! No I haven't checked how much water is pouring into the resonator, but I do know from flushing yesterday this lasted about a minute. And when I was at the dock it seemed to last longer until I clamped the hose to the water valve so I wouldn't get stuck.

I may have fixed my issue with tying up the hoses in a high loop, but still hearing the water pouring in concerned me.

I can disconnect that hose next time and let it drain into an empty 1 gallon bucket. If it exceeds 1 gallon then something is for sure a miss there.

I still don't know why I have to go through this extra effort of clamping that hose when others do not. But if I don't do that, I run the risk that at some point I will be stuck.

I would like to understand the theory here. I do understand the water flow from the cooling diagrams, I just don't know why my rotax 787 differs from others.

 

[wernerml]

I know my Challenger is set up as it came from the factory. Both cooling hoses from the jet pump, and flush fitting are looped up to the underside of the engine compartment near the hinges for the hood.

I would expect that water from the exhaust would run into the resonator after shut down.

 

[mejim707]

I know my Challenger is set up as it came from the factory. Both cooling hoses from the jet pump, and flush fitting are looped up to the underside of the engine compartment near the hinges for the hood.

I would expect that water from the exhaust would run into the resonator after shut down.

This is great news! Can you post a few pictures of your factory cooling routing if it's not too much trouble? I would love to see how it's routed from the factory!

 

[mejim707]

Update: So I revised my cooling hose routing to match what @wernerml has. It's cleaner and now at least I know it's factory routing.

However, I docked yesterday and that pouring sound lasted the entire time I was at the dock. I let it go to see what would happen. The water is actively pouring into the resonator, through the large lower hose on the water regulator for 15+ minutes straight. This is filling the exhaust.

I tried to start and as expected it wouldn't attempt to start. I figured this would happen because I heard this pouring sound for so long.

I clamped the inlet hose, and water regulator hose and tried to start it. After about 30 seconds it fired up. You can hear it ejecting the water out of the exhaust system and when it clears it enough it fires up.

NOTE: I can clamp both the inlet hose from the jet pump, and the hose going to the head after the "T" for the water regulator. But, this water sound persists. It does not stop until I clamp the large lower hose going to the water regulator. It's as though pressure from the heated exhaust is drawing in water from some other place and clamping the hose on the water regulator is the only way to stop this flow.

There is absolutely something amiss here with this water regulator or the exhaust. I'm missing something. Functionally, this is the only issue with the boat right now.

 

[wernerml]

The water regulator you are talking about is the modified RAV on top of the exhaust resonator. Have you verified the operation of that valve?
According to the shop manual water flows to the resonator all the time , but through a calibrated hole. The valve uses water pressure to shut off water flow upstream to the exhaust "for noise reduction and performance improvement."

The bellows and bellows clamps can be damaged by corrosion and age.

You can replace the clamps with small zip ties. If the bellows has a hole you will need to get a replacement. Because it is attached to the exhaust carbon and oil can gum it up and keep it from working. The shop manual has a calibration procedure. There are you tube videos out there in this valve.

 

[wernerml]

Is the upper end of the flushing line capped and not leaking? Letting air in would allow the water in the upper parts of the engine and exhaust to flow back to the jet inlet and the water regulator.

 

[mejim707]

Is the upper end of the flushing line capped and not leaking? Letting air in would allow the water in the upper parts of the engine and exhaust to flow back to the jet inlet and the water regulator.
View attachment 60294

So I took the water regulator off and inspected it inside and out. I disassembled it and inspected each part. It's all in perfect condition and seems to be brand new. From what I see, the lower hose, from the "T" on the inlet, has direct flow of water into the water valve and directly down into the resonator.

Also, the upper cap for the flushing hose is on and tight with a rubber bushing. However, the flush port from under the sun deck in the rear is always open and not capped off. From the research I've done this is supposed to always be open and never capped off. People say never cap it. So if that's not capped off, then the flush lines will always be free flowing.

So, this regulator looks new, but something to do with this setup water is pouring into the resonator, enough to fill the exhaust, with nothing restricting it unless I clamp that lower hose on the water regulator. Then instantly the flow of water stops, and I have no starting issues. In fact, I have such confidence in this I can stop the boat while in the middle of the lake and stay there as long as I want with the engine off so long as that lower water regulator hose is clamped and it will fire up every time. If I don't clamp it, forget it. I'm dead in the water.

Truly bazaar issue.

 

[Spider4real]

My flush connector under the sun deck was capped off. And as per the shop manual it is supposed to be capped off.

 

[mejim707]

My flush connector under the sun deck was capped off. And as per the shop manual it is supposed to be capped off.

Whoa whoa whoa.... I've read so many places that the one under the sun deck was supposed to be open, and people were like "I don't know why they made it threaded" haha They were saying it needs to be open because too much water pressure could fill the engine so this remaining open will prevent that. Some went so far as to say "never cap it off".

But from what you're saying, you have it capped. Can you take a picture of it capped off? I'm talking about the one under the rear deck next to the jet pump. The threaded flushing port.

Also, please point to where this is in the manual. I totally agree, if the manual says to cap it, then I will absolutely do so.

I've researched this so many times and I never found one person say to make sure a cap is on that flushing port. I only found the opposite.

 

[Spider4real]

Sorry I don't consider that a sun deck. I was talking about the one under the trunk next to the blower hole.

The one on the transom, next to the jet pump is supposed to be open. Water needs to get out of that one. It's calibrated to allow a certain amount out.

 

[wernerml]

Yes, the top side one is capped, the one under the swim platform must be open.

It is threaded to fit a 3/4" garden hose fitting for flushing. This should be used only when the engine is running. For use after every outing in saltwater. ( I never use it here in Lake Michigan)

Here is a wild idea. How about a check valve in line with the hose from the jet pump to the bottom fitting on the water regulator. Direction of flow towards the regulator. While running it wouldn't be much of a restriction. But as soon as you shut down a few inches of water head wouldn't push past the check valve. It's not stock but may solve your issue. Or at least give you another data point in your investigation.

Is your boat loaded up with lots of bodies? When at max load the flush fitting may be under water and lead to your problem. I have a rubber stopper in my cockpit drain for this condition because that flapper valve in the transom doesn't work for crap .

The engine drain hose goes to the exhaust through transom fitting and shouldn't be putting water in the resonator.

 

[mejim707]

Yes, the top side one is capped, the one under the swim platform must be open.

It is threaded to fit a 3/4" garden hose fitting for flushing. This should be used only when the engine is running. For use after every outing in saltwater. ( I never use it here in Lake Michigan)

Here is a wild idea. How about a check valve in line with the hose from the jet pump to the bottom fitting on the water regulator. Direction of flow towards the regulator. While running it wouldn't be much of a restriction. But as soon as you shut down a few inches of water head wouldn't push past the check valve. It's not stock but may solve your issue. Or at least give you another data point in your investigation.

Is your boat loaded up with lots of bodies? When at max load the flush fitting may be under water and lead to your problem. I have a rubber stopper in my cockpit drain for this condition because that flapper valve in the transom doesn't work for crap .

The engine drain hose goes to the exhaust through transom fitting and shouldn't be putting water in the resonator.

I have a rubber plug for the floor water drain as well lol The ball valve on the transom doesn't work well at all.

I'll leave the transom flush connector open. It has no cap and I'm glad the consensus is that it should not. The one under the hood does however.

It's only me that goes out with the boat. So 1 person and maybe 25 pounds of gear on board and that's all. Nothing to make the rear low in water. I weight maybe 160 wet haha

I could try the check valve idea, but if I'm working on anything the deviates from stock, couldn't I delete the water regulator all together? I've heard of people doing this but I don't want to cause an issue. I'd imagine this would only force more water into cooling the exhaust and shouldn't cause harm?

 

[wernerml]

Yes, the top side one is capped, the one under the swim platform must be open.

It is threaded to fit a 3/4" garden hose fitting for flushing. This should be used only when the engine is running. For use after every outing in saltwater. ( I never use it here in Lake Michigan)

Here is a wild idea. How about a check valve in line with the hose from the jet pump to the bottom fitting on the water regulator. Direction of flow towards the regulator. While running it wouldn't be much of a restriction. But as soon as you shut down a few inches of water head wouldn't push past the check valve. It's not stock but may solve your issue. Or at least give you another data point in your investigation.

Is your boat loaded up with lots of bodies? When at max load the flush fitting may be under water and lead to your problem. I have a rubber stopper in my cockpit drain for this condition because that flapper valve in the transom doesn't work for crap .

The engine drain hose goes to the exhaust through transom fitting and shouldn't be putting water in the resonator

I have a rubber plug for the floor water drain as well lol The ball valve on the transom doesn't work well at all.

I'll leave the transom flush connector open. It has no cap and I'm glad the consensus is that it should not. The one under the hood does however.

It's only me that goes out with the boat. So 1 person and maybe 25 pounds of gear on board and that's all. Nothing to make the rear low in water. I weight maybe 160 wet haha

I could try the check valve idea, but if I'm working on anything the deviates from stock, couldn't I delete the water regulator all together? I've heard of people doing this but I don't want to cause an issue. I'd imagine this would only force more water into cooling the exhaust and shouldn't cause harm?

Did you look at the cooling circuit picture I posted? There are some notes there that give some ideas of how it's all supposed to work.

The tuned pipe performance is affected by temperature due to the change in the speed of sound in the pipe. A warmer pipe is tuned to a higher RPM because the pressure wave travels faster. That's probably why they cool it with extra water at lower RPM. The water into the resonator is probably for cooling and noise reduction. Not sure how toasty that would get get without the water.


Still thinking something not quite right with your water regulator valve. The spring was in there, correct? You said it looks new, I wonder if it was the correct one for this boat? Maybe too large of a hole to pass water into the resonator. Starting to guess here...

 

[mejim707]

Yes, the top side one is capped, the one under the swim platform must be open.

It is threaded to fit a 3/4" garden hose fitting for flushing. This should be used only when the engine is running. For use after every outing in saltwater. ( I never use it here in Lake Michigan)

Here is a wild idea. How about a check valve in line with the hose from the jet pump to the bottom fitting on the water regulator. Direction of flow towards the regulator. While running it wouldn't be much of a restriction. But as soon as you shut down a few inches of water head wouldn't push past the check valve. It's not stock but may solve your issue. Or at least give you another data point in your investigation.

Is your boat loaded up with lots of bodies? When at max load the flush fitting may be under water and lead to your problem. I have a rubber stopper in my cockpit drain for this condition because that flapper valve in the transom doesn't work for crap .

The engine drain hose goes to the exhaust through transom fitting and shouldn't be putting water in the resonator

Did you look at the cooling circuit picture I posted? There are some notes there that give some ideas of how it's all supposed to work.

The tuned pipe performance is affected by temperature due to the change in the speed of sound in the pipe. A warmer pipe is tuned to a higher RPM because the pressure wave travels faster. That's probably why they cool it with extra water at lower RPM. The water into the resonator is probably for cooling and noise reduction. Not sure how toasty that would get get without the water.


Still thinking something not quite right with your water regulator valve. The spring was in there, correct? You said it looks new, I wonder if it was the correct one for this boat? Maybe too large of a hole to pass water into the resonator. Starting to guess here...

So when I pulled the water valve, the lower hose nipple can flow water directly in and down into the resonator with nothing preventing it. The entire upper / functional part of the regulator seems to have no bearing on the water entering the resonator from the inlet hose at the "T". From what I see, the water can flow without restriction into the resonator and the water valve cannot prevent this.

I studied the pictures you posted and revised my cooling routing. Thank you again for that! All the hoses were in the correct spot, but I changed how the flush hoses were routed and updated the inlet hose to route it, and tie it in a high loop exactly as your boat has it so it would be 1:1. Unfortunately this didn't correct the issue.

It's as though the hot inside of the exhaust is creating a vacuum effect and pulling water in from somewhere until I clamp that lower hose to the regulator. Then it immediately stops.

As for the water regulator function, from my understanding and please correct me if I'm wrong, the higher RPMs cause water pressure to push up on the inside of the bellow, overcoming the preload of the spring, and as the bellow pushes up, the tapered screw will then close off the opening to the upper hose and at that point all the water is shot directly into the resonator. At lower RPMs the water can flow into the resonator as well as the upper hose into the tuned pipe. Is this correct?

 

[wernerml]

Yes, that's the way the water regulator is designed to work. I think there is an orifice in the path to the resonator that limits the water going there. But that could still be relatively large 0.125" as a wild guess.

I'm planning on going for a ride tomorrow, I'll try to see if I can hear your water flow issue.

 

[makaveli07]

So when I pulled the water valve, the lower hose nipple can flow water directly in and down into the resonator with nothing preventing it. The entire upper / functional part of the regulator seems to have no bearing on the water entering the resonator from the inlet hose at the "T". From what I see, the water can flow without restriction into the resonator and the water valve cannot prevent this.

I studied the pictures you posted and revised my cooling routing. Thank you again for that! All the hoses were in the correct spot, but I changed how the flush hoses were routed and updated the inlet hose to route it, and tie it in a high loop exactly as your boat has it so it would be 1:1. Unfortunately this didn't correct the issue.

It's as though the hot inside of the exhaust is creating a vacuum effect and pulling water in from somewhere until I clamp that lower hose to the regulator. Then it immediately stops.

As for the water regulator function, from my understanding and please correct me if I'm wrong, the higher RPMs cause water pressure to push up on the inside of the bellow, overcoming the preload of the spring, and as the bellow pushes up, the tapered screw will then close off the opening to the upper hose and at that point all the water is shot directly into the resonator. At lower RPMs the water can flow into the resonator as well as the upper hose into the tuned pipe. Is this correct?

I dont mean to hijack this thread, but I’m having a similar problem, i hear water syphoning in the resonator after turning off and the boat takes 5-7 seconds of cranking to start after being off for 10 minutes. Im wondering if you manged to fix this problem and if so how did you fix it? Everything on my boat is rebuilt ( literally full restoration done). But this issue is a bit annoying as it takes 5-7 seconds of cranking to start the boat after being off for 10 minutes. I can audibly hear water going into the resonator. Here is what my routing looks like.

 

[mejim707]

I dont mean to hijack this thread, but I’m having a similar problem, i hear water syphoning in the resonator after turning off and the boat takes 5-7 seconds of cranking to start after being off for 10 minutes. Im wondering if you manged to fix this problem and if so how did you fix it? Everything on my boat is rebuilt ( literally full restoration done). But this issue is a bit annoying as it takes 5-7 seconds of cranking to start the boat after being off for 10 minutes. I can audibly hear water going into the resonator. Here is what my routing looks like.

EXACTLY! Sadly I still haven't found the issue but that's exactly what's happening to me.

BTW, your engine bay looks MINT! I love it. I want to pull my motor this winter and paint it to get it a step closer to looking this clean lol

So, what I found is that this only happens when you shut the boat off on water after running a while. This never happens when cold. But when warm, and you shut it off, I very clearly hear water flowing into the resonator and filling it. This does not stop and will continue to flow in regardless of how long I wait until the exhaust is full. For me, I will never be able to start it on water like this. This does not get any water into the cylinders though. Only the bottom of the exhaust to bog it out.

The only thing I've been able to do to prevent this is to put a hose pincher on the lower hose of the water regulator. This prevents water from pouring in and the boat starts instantly every time.

This is annoying of course but not a deal breaker for a fun day. But I really want to figure this out and based on the fact you have the same issue, with a fresh rebuild, makes me really think we're missing some basic thing causing this issue.

Only thing I would suggest for you, because others told me to do it, is to tie that loop from the jet pump in a high loop to attempt at breaking the siphoning effect. Maybe this will solve your issue, but please keep me posted.

 

[wernerml]

I finally had a long ride late last week. Shutting down brought the sound of water running into the resonator. That stopped after 3~4 minutes.

The routing of the cylinder drain line lays in the bottom of the bilge. So does the hose from the regulator to the tuned pipe. Finally the hose from the top of the exhaust to the CSI (cooling system indicator) is routed pretty straight and level.

I am hypothesizing maybe something like the CSI line is not allowing air into the top of the exhaust. This would keep water from running out the cylinder block drain to the exhaust exit at the stern of the boat .

This keeps the cylinder water jackets full of water and it runs into the resonator.

A plugged cylinder drain line could hold water in the engine which would then drain into the resonator.

When I winterize my engine I pinch the inlet and flush lines, and connect my air compressor to the CSI outlet. This forces most of the water out the cylinder drain line, reducing the amount of antifreeze I need to put in. You could use a similar approach to verify that drain line is clear.

Doesn't seem like enough water in the upper parts of the engine to cause your problem, but...

Grasping at straws here.

 

[mejim707]

I finally had a long ride late last week. Shutting down brought the sound of water running into the resonator. That stopped after 3~4 minutes.

The routing of the cylinder drain line lays in the bottom of the bilge. So does the hose from the regulator to the tuned pipe. Finally the hose from the top of the exhaust to the CSI (cooling system indicator) is routed pretty straight and level.

I am hypothesizing maybe something like the CSI line is not allowing air into the top of the exhaust. This would keep water from running out the cylinder block drain to the exhaust exit at the stern of the boat .

This keeps the cylinder water jackets full of water and it runs into the resonator.

A plugged cylinder drain line could hold water in the engine which would then drain into the resonator.

When I winterize my engine I pinch the inlet and flush lines, and connect my air compressor to the CSI outlet. This forces most of the water out the cylinder drain line, reducing the amount of antifreeze I need to put in. You could use a similar approach to verify that drain line is clear.

Doesn't seem like enough water in the upper parts of the engine to cause your problem, but...

Grasping at straws here.

I do see water coming out of the weep hole at the exhaust pipe which comes form the lower drain hoses of the engine. But I will absolutely recheck the drain hoses. I'll pull the lower tuned pipe and check that there are no clogs there.

 

[POPPS]

Does your symptom have any similarities the automotive cooling system,,,where after you shut the engine off,,water syphons into the collection container.. ?