Sea doo exhaust system flushing question

[PGVR]

Hi there,

When flushing the exhaust system the the sea doo manual states that one must first start the engine then only switch on the tap/water. If water is turned on before starting the engine 'water will get inside the engine'.

Can someone please explain this?

Do they mean enter the engine compartment/hull or that the water actually enters the exhaust outlet on the engine?

When motoring on a lake/ocean does the water actually flow through the exhaust system or around it or just through the jet? Need to understand the flow of water during motoring and during a flush.

Help will be greatly appreciated.

 

[PGVR]

Ok, I took a closer look and found the following:

• the flushing connector is connected to the bottom end of the exhaust manifold
• When the motor is running the exhaust pressure forces the water through the exhaust system and out the jet

The unanswered question though is 2.) While motoring on lake/ocean does this flushing connector act like a venturi and suck in the water and out through the exhaust system?

View attachment 55292

 

[Whus02]

The water is pressurized by the jetpump, before flowing to the rest of the system. The flow of the exhaust prevents the water from entering the engine. So no, the system is not reliant on a venturi effect.

 

[Hndyman55]

So the water will get into the engine and contaminate the engine oil? I have ran the water before starting the ski and after shutting the motor off. Just like running a boat on muffs. So far I haven’t noticed any water in the oil. However I will start doing it the correct way.

 

[Whus02]

The water won't necessarily enter the engine oil, but it will enter the combustion chamber through the exhaust, it is definitely recommended to follow the procedure to minimize the chance of this occuring.

 

[Hndyman55]

So is it possible to hydrolock it?

 

[Whus02]

So is it possible to hydrolock it?

Yes sir.

 

[PGVR]

Whus02, not sure what you mean by the water is pressurised by the jet pump. Also what is 'to the rest of the system'? Is the flow of water as I have shown in the diagram correct though?

If it is pressurised then surely the water will be forced back towards the flushing connector?

 

[skiasylum]

Exhaust system description,

The exhaust system is cooled by water provided by a pressurized area in the jet pump. (open loop system)
The same water is used to cool the intercooler and IBR motor if so equipped.
So normal operations pressurized water first goes to the exhaust manifold jacket, then by hoses is directed to the exhaust pipe, muffler, and resonator for cooling then on to the ibr motor and intercooler if so equipped. Water exits the exhaust pipe water jacket thru small holes and is then injected into the muffler and resonator for cooling and then out the back thru the exhaust outlet in the transom area.

Now non normal operations (flushing)

There is a one way check valve on the flush line just inside the transom that prevents pressurized water from flowing out the flush fitting during normal operations. The problem arises when you flush the exhaust system without exhaust gasses (engine not running), water then collects in the muffler and resonator thru the little cooling holes in the exhaust pipe water jacket because it is not mixed with exhaust gasses and carried out the back with the exhaust. So depending on how much water pressure and how long you do this effects how much water collects in the muffler and resonator. No harm done yet. Now if you have improperly flushed and a large amount of water has collected in the muffler and resonator and you start the motor you just activated a big vacuum pump and water can then be sucked into the intake system from the exhaust system into the intake manifold thru the intake valves into the engine and oil. Water flooded engine scenario.

So if you improperly flush your exhaust system, anytime water is on and engine not running, and you think you have water collected in the exhaust system, pull your muffler and make sure water is not trapped inside.

 

[Milehighguy303]

I will share a little, and there will probably be others that can give better detail with more experience.
When riding, there is a portion of the water that is pushed out the jet pump to propel you forward, routed thru a hose into the exhaust manifold and cooling chamber. You could estimate about 95% of the water goes thru the jet pump out the back of the ski and 5% is pumped, under pressure, into the exhaust manifold and cooling chamber. The exhaust from the engine pushes the water thru the manifold, cooling chamber (that large metal canister) and out the exhaust hole near the jet pump.
Your flush from a garden hose does what the jet pump does when you are riding. The ski hose routing to the exhaust system may route slightly differently than the jet pump cooling hose. You can probably find the hose in the hull where you attach a garden hose and follow it in the hull to where it attaches to either the exhaust manifold or cooling chamber. I think on my 2007 GTI SE 155 the garden hose water goes into the cooling chamber, not the manifold, but not 100% sure. But the point is, that your garden hose is cooling the exhaust, and flushing out lake water, salt water, possible organisms in the exhaust, etc.
You are probably beginning to tell that it is critical to have the engine running, providing the exhaust pressure pushing water thru the exhaust cooling system, before you turn on your garden hose. Because of the engine isn’t running, you will fill the exhaust manifold and cooling chamber with water, and then water will back up into the engine, going into cylinders with open exhaust valves, and leaking slowly in cylinders with closed exhaust valves. This creates the Worst nightmare for any ski owner - a water filled and locked cylinder or two. The engine won’t be able to turn over, and the compression stroke pressure in the cylinder pushes the water past the piston rings into the oil crankcase at the bottom of the engine. And it sucks. I know all about it when my ski cooling hose from the jet pump to my exhaust manifold came off in February and so water (salt mind you) was not getting to my manifold and was filling my hull up until I sank. Long story…but it has a happy ending. You can read my posts from February and March this year if you want a nice bedtime story. Hope this general description helps - someone with more knowledge can maybe explain exactly where the garden hose flush connection on your ski comes into the exhaust system.
And yes, there is a Venturi effect that you have to be concerned about when towing a disabled ski that is not running. Read the owner manual for your ski. There is a speed limit you should not exceed, or on older skis they recommended you pinch off your hose from the jet pump to the manifold, to prevent water from working its way into your exhaust manifold with the engine off, causing the same water locked engine situation I explained from the garden hose.

 

[PGVR]

Thanks to all, this makes sense now.

 

[Hndyman55]

Yes very informative!

 

[PGVR]

I will share a little, and there will probably be others that can give better detail with more experience.
When riding, there is a portion of the water that is pushed out the jet pump to propel you forward, routed thru a hose into the exhaust manifold and cooling chamber. You could estimate about 95% of the water goes thru the jet pump out the back of the ski and 5% is pumped, under pressure, into the exhaust manifold and cooling chamber. The exhaust from the engine pushes the water thru the manifold, cooling chamber (that large metal canister) and out the exhaust hole near the jet pump.
Your flush from a garden hose does what the jet pump does when you are riding. The ski hose routing to the exhaust system may route slightly differently than the jet pump cooling hose. You can probably find the hose in the hull where you attach a garden hose and follow it in the hull to where it attaches to either the exhaust manifold or cooling chamber. I think on my 2007 GTI SE 155 the garden hose water goes into the cooling chamber, not the manifold, but not 100% sure. But the point is, that your garden hose is cooling the exhaust, and flushing out lake water, salt water, possible organisms in the exhaust, etc.
You are probably beginning to tell that it is critical to have the engine running, providing the exhaust pressure pushing water thru the exhaust cooling system, before you turn on your garden hose. Because of the engine isn’t running, you will fill the exhaust manifold and cooling chamber with water, and then water will back up into the engine, going into cylinders with open exhaust valves, and leaking slowly in cylinders with closed exhaust valves. This creates the Worst nightmare for any ski owner - a water filled and locked cylinder or two. The engine won’t be able to turn over, and the compression stroke pressure in the cylinder pushes the water past the piston rings into the oil crankcase at the bottom of the engine. And it sucks. I know all about it when my ski cooling hose from the jet pump to my exhaust manifold came off in February and so water (salt mind you) was not getting to my manifold and was filling my hull up until I sank. Long story…but it has a happy ending. You can read my posts from February and March this year if you want a nice bedtime story. Hope this general description helps - someone with more knowledge can maybe explain exactly where the garden hose flush connection on your ski comes into the exhaust system.
And yes, there is a Venturi effect that you have to be concerned about when towing a disabled ski that is not running. Read the owner manual for your ski. There is a speed limit you should not exceed, or on older skis they recommended you pinch off your hose from the jet pump to the manifold, to prevent water from working its way into your exhaust manifold with the engine off, causing the same water locked engine situation I explained from the garden hose.

Exhaust system description,

The exhaust system is cooled by water provided by a pressurized area in the jet pump. (open loop system)
The same water is used to cool the intercooler and IBR motor if so equipped.
So normal operations pressurized water first goes to the exhaust manifold jacket, then by hoses is directed to the exhaust pipe, muffler, and resonator for cooling then on to the ibr motor and intercooler if so equipped. Water exits the exhaust pipe water jacket thru small holes and is then injected into the muffler and resonator for cooling and then out the back thru the exhaust outlet in the transom area.

Now non normal operations (flushing)

There is a one way check valve on the flush line just inside the transom that prevents pressurized water from flowing out the flush fitting during normal operations. The problem arises when you flush the exhaust system without exhaust gasses (engine not running), water then collects in the muffler and resonator thru the little cooling holes in the exhaust pipe water jacket because it is not mixed with exhaust gasses and carried out the back with the exhaust. So depending on how much water pressure and how long you do this effects how much water collects in the muffler and resonator. No harm done yet. Now if you have improperly flushed and a large amount of water has collected in the muffler and resonator and you start the motor you just activated a big vacuum pump and water can then be sucked into the intake system from the exhaust system into the intake manifold thru the intake valves into the engine and oil. Water flooded engine scenario.

So if you improperly flush your exhaust system, anytime water is on and engine not running, and you think you have water collected in the exhaust system, pull your muffler and make sure water is not trapped inside.

One more question, when motoring on water is it ok to leave the water flush inlet port open or closed off with an end cap?

When motoring on water does water get 'sucked' up into the flush inlet port into the flushing system?

Is there any disadvantage in sealing the port off when motoring on water?

 

[skiasylum]

The check valve just inside the transom prevents water from entering the flush system unless there is outside pressure (hose pressure), there is no disadvantage in sealing the port off when motoring but it is already sealed so it would be redundant.

 

[ski-d00]

Not aware of any check valve on the flush port.(there are check valves on the drain plugs) When flushing on the hose, the water flow direction is backwards. So with the ski in the water the flush port is an exit but only a minor flow exit compared to the exhaust so doesn't matter if it is plugged or not really but not recommended to plug.

 

[Hndyman55]

If there are check valves on the (2) drain plugs, why have plugs? Those are to drain the bilge. A check valve wouldn’t let it drain I have seen aftermarket one way valves installed so water can’t flow back in but on my 2011 there are no check valves on the drain plugs.

 

[ski-d00]

Yes, there are check valves on your 2011. It lets the water flow out and not flow in if you leave the plug out. Just a safety system really.

The system is not great and usually works okay but they tend to clog and may leak some and also don't let water drain out of the ski very well. I've taken out skis for people that left them out all summer but have had others that sank in a day.

 

[Hndyman55]

That’s crappy. I’ll have to take a closer look at mine

 

[skiasylum]

“There is a check valve in there, but it operated the opposite direction than you think... the check valve prevents water circulating from the jet pump from pouring out that flush port when you're operating on the water (hence, you don't have to manually block the port off or anything).”

Pretty sure there is a check valve.

 

[ski-d00]

I've disassembled lots of skis and don't ever recall seeing a check valve on any exhaust system. What year and model? Where is it on the parts diagram and what part number?

There is a check valve in there, but it operated the opposite direction than you think

Well, if it operated where it only let water out and didn't let any water in then it wouldn't be a very good flush port. lol

 

[PGVR]

I've disassembled lots of skis and don't ever recall seeing a check valve on any exhaust system. What year and model? Where is it on the parts diagram and what part number?

Well, if it operated where it only let water out and didn't let any water in then it wouldn't be a very good flush port. lol

That is exactly what I was thinking. A flush port only letting water out makes for a real crap flush port.

My common sense says that when motoring on water that somehow water may be sucked up into the flush port due to the exhaust port creating a venturi effect.

A simple diagram showing all the water pipe connections/flow will be super useful. If I have a few hours spare I will try to put something together.

 

[skiasylum]

My last post was a quote from Green Hulk discussion on exhaust cooling, the check valve we are referring to only lets water in the flush port. All the parts diagrams on the exhaust cooling system are horrible to read at best. I also could not find a specific part # for any check valve in the exhaust cooling system. It might be incorporated in the flush port itself.

So would someone please disconnect the hose going from the flush port to the muffler and blow into it from the muffler side of the hose to verify whether there is a check valve or not. lol

 

[PGVR]

That is a big blowj0b to do. Hard to get down that low, and its hard to get in there. I will give a go this weekend!