Rope clog-

[0wen87]

Well... I sucked up a rope. After cutting it, I followed instructions and attempted to clear the boat with throttle. In doing so, I think some type of exhaust coupler in the engine compartment blew off. One engine got loud ansome smoke filled the compartment. I shut it down and cooled it off but can't find where the exhaust exits the boat. Any quick pointers?

255 / 250hp

 

[Bruce]

@DieselCamel, does this sound familiar?

 

[DieselCamel]

Unfortunately yes, sounds like you may have a clog on the exhaust side of the cooling system. My was clogged with seaweed and melted the coupler for the water box.. I think this is the right diagram ( I'm in my phone)

 

[0wen87]

Looks like I have blown a hole in the muffler. Geezzz.....

Would the ski rope being sucked up clog the exhaust cooling?

 

[DieselCamel]

Looks like I have blown a hole in the muffler. Geezzz.....

Would the ski rope being sucked up clog the exhaust cooling?

anything is possible. but highly unlikely

 

[ScarabMike]

These engines are closed loop (no raw water), so the ingestion of the rope wouldn't have done damage to the system, but the rattling would. The diagram above is completely different from what we have on our boats. If you are getting exhaust sounding louder than normal with fumes, check the water box hose prior to the water injection. Its a large hose coming off of the exhaust manifold into the water box. It may have come loose where it will leak under load.

 

[funbobby]

These engines are closed loop (no raw water), so the ingestion of the rope wouldn't have done damage to the system, but the rattling would. The diagram above is completely different from what we have on our boats. If you are getting exhaust sounding louder than normal with fumes, check the water box hose prior to the water injection. Its a large hose coming off of the exhaust manifold into the water box. It may have come loose where it will leak under load.

The engine cooling is closed loop, but the exhaust cooling is open loop fresh water.

 

[ScarabMike]

The engine cooling is closed loop, but the exhaust cooling is open loop fresh water.

The rope will not cause the failure. He is getting exhaust, and sound with no water intrusion. This means the issue is before the water inlet to the exhaust system.

 

[Julian]

So a Scarab with a clogged pump still gets water flow to cool the exhaust and run through the heat exchanger? Does it have a separate water pump and intake somewhere?

 

[itsdgm]

How long did the engine run on the water with a rope in the pump? I would think it's possible that with a rope in the pump/shaft that limited amounts of water to the exhaust cooling system could cause that damage. No?

 

[Julian]

I followed instructions and attempted to clear the boat with throttle

I cant imagine a rope EVER clearing just with throttle....does the manual actually say this????

I imagine your intake looks something like this (a Seadoo)-that isn't going away without manual intervention:

 

[0wen87]

I pulled the coupler off of the water box and can see a hole in the bottom of it. And I mean a big hole (fist size). The manual addresses "debris", which might not include "rope".. but I did notice that the manual wasn't very model or size specific. The engine only ran for 2 minutes (or less) with the rope. I limped back on 1 motor, cut out what I could get to (in the water) and then cranked the engine (it didn't want to turn over at first) and throttled it a few times to try to clear the pieces.. That is when erratic reving and heavy vibrations began. I shut 'er down again and limped back to the dock. After the engine cooled, I fired it up and heard the exhaust blurping in the engine compartment. I was checking all of the couplers when I found the hole.

 

[ScarabMike]

@Julian The Rotax engines have a stainless steel shaft sleeve to prevent that from happening, although I have still seen it done. But the sleeve will allow the boat to limp back home.

@0wen87 If your water box has a hole in it, you need to take the boat in. Water intrusion, carbon monoxide poisoning, and possible fire due to heat.

 

[Julian]

@Julian The Rotax engines have a stainless steel shaft sleeve to prevent that from happening, although I have still seen it done. But the sleeve will allow the boat to limp back home.

@0wen87 If your water box has a hole in it, you need to take the boat in. Water intrusion, carbon monoxide poisoning, and possible fire due to heat.

Just because the shaft has a sleeve doesnt prevent ingestion and wrapping it around the shaft....like this post proves (and other ones too...and others). I get that the impeller MIGHT still spin, but not guaranteed. Also, without water flowing through the jet pump (and unless it has a water pump I'm not aware of) the boat will still overheat because the heat exchanger wont be fed water from the jet unit (again...unless the jet pump isn't the heat exchangers source of coolant).

 

[ScarabMike]

@Julian The heat exchanger does not use raw water, it uses coolant. The engine is just like a car and has its stand alone pump. The heat exchanger just uses the surface of the water to help with the dissipation of heat just like a radiator using air. Raw water never touches any engine components.

The exhaust needs raw water to cool it, and the intercooler uses raw water as well.

 

[Julian]

@Julian The heat exchanger does not use raw water, it uses coolant. The engine is just like a car and has its stand alone pump. The heat exchanger just uses the surface of the water to help with the dissipation of heat just like a radiator using air. Raw water never touches any engine components.

The exhaust needs raw water to cool it, and the intercooler uses raw water as well.

OK, so it is exactly as I thought. Without water flowing through the pump, the exhaust and heat exchanger will get no coolant. The exhaust will melt first, followed by the engine much later, but eventually it will over heat too. Just like an engine running on a non-moving car on which the fan belt break without an electric fan running on the radiator. Hopefully in this case, only the exhaust was damaged. My point is, just because this is a closed loop system doesn't mean it will run ok without cooling water from the jet pump. If the jet pump is clogged you have a serious cooling problem on your hands. One that will melt your exhaust first, then your engine.

 

[0wen87]

Was I wrong to turn that engine off and limp back on a single? I have to get the boat to the landing tomorrow, which is 4-5 miles away..

 

[ScarabMike]

No water needs to be flowing through the heat exchanger @Julian . Just the contact of the SURFACE of the water on the exchanger. The engine will NOT overheat. It does NOT need any water from the jet pump. The rotax does not cool like any traditional marine engine. You could have a naturally aspirated Rotax with the exhaust disconnected, and it will run normally on the water.

Refer to page 61/62 of the service manual. Part number 6 is the engine's coolant pump. You can see its self sustained, and has its own impeller that is driven by a PTO and the crankshaft.
http://seadoomanuals.net/download/pdf/service/manuals/2005/2005-seadoo-rotax-1503-4-tech-shop-manual.pdf

You are correct on the exhaust, but it will take running the boat full throttle for some time without water flowing through it to melt it. You can limp home at partial throttle and it will be ok.
This is why we wanted a Rotax section. This would be explained in depth.

The only way the rotax will overheat is: No SURFACE contact (like when you are flushing the system outside the water), coolant leak, or engine water pump failure.

OK, so it is exactly as I thought. Without water flowing through the pump, the exhaust and heat exchanger will get no coolant. The exhaust will melt first, followed by the engine much later, but eventually it will over heat too. Just like an engine running on a non-moving car on which the fan belt break without an electric fan running on the radiator. Hopefully in this case, only the exhaust was damaged. My point is, just because this is a closed loop system doesn't mean it will run ok without cooling water from the jet pump. If the jet pump is clogged you have a serious cooling problem on your hands. One that will melt your exhaust first, then your engine.

Was I wrong to turn that engine off and limp back on a single? I have to get the boat to the landing tomorrow, which is 4-5 miles away..

Absolutely not. You used the system as it was intended. You will be fine.

 

[ScarabMike]

Also, just in case the question arrises, the Rotax cooling system's effective RPM are 670 rpm as a minimum. That means the engine could be spinning at 670 rpm, and the cooling system will operate as intended. Thus being able to limp home with no issue even with the impeller obstruction. I hope I have made this clear enough.

 

[Julian]

@ScarabMike ah....got it! Basically, the ride plate is the heat exchanger! (took me a while! LOL) I still think reving an engine with a clogged pump is a recipe for a melt down of the exhaust. I'll bet if you do that for more than about 3-4 minutes something will melt....