I have a 1996 Sea Doo Challenger with 787. This spring I found that one of the plugs on my exhaust manifold had corroded through so I removed the manifold and alumiwelded the hole closed. It seemed to be a solid repair.

• Seadoo Challenger Specs
• 1997 Seadoo Challenger Service Manual

So I put all the parts back together and even used RTV gasket material. So the boat runs fine, but after a while of running at 6-7000 rpm I noticed some smoke in the engine compartment and noticed that the exhaust manifold which had been purple was now black (when I heated the other part of the exhaust manifold in the barbeque grill to facilitate the alumiwelding it turned the same color of almost black).

The engine seemed hot so I poured a little water on the manifold and it steamed. At all times I got the little pee stream out the back of the boat which seemed maybe slightly warmer than the lake water. I ran at idle back to the dock and when there I noticed the manifold was cool to the touch and the engine seemed to run fine. So can anyone tell me what is happening here? Is there an obstruction in a hose maybe?

Seadoo Challenger Specs

Did i inadvertantly block something with my welding? Is it possible the boat is getting just enough water to cool at idle speed but not at high RPM? Is there something I can check at the dock without pulling out the boat? Keep in mind that competent mechanics in this area are rarer than winning lottery tickets. Last year the shop had my boat from May 15 until Oct 28 so I am reluctant to give up yet another season to have it sit in a back lot. Look at the line going to the water control valve on the water box.

Did the coupler between the pipe and the water box get soft? Is the pipe discolored before the little coupler before the water box? The wcv diaphragm could be bad and leaking water or the valve has failed. Pull the line off from the front of the head cover to the pipe, is a half inch hose. Take a mirror and look in the fitting off the front of the head, is it corroded internally?

These are typical issues. Post a pic of the pipe, that will point is I the right direction. OK, I pulled the hose from the cylinder head to the exhaust manifold pipe.

It was clear. I started the motor and water came out of the head at a pretty good stream. So what next? I wonder if the obstruction is inside the manifold itself. Is there anyway to see where the water comes out of the manifold without pulling the manifold off the engine again? Keep in mind that the boat is in the water and the trailer is kind of hard to get to.

Another question is: how warm is the exhaust manifold supposed to get? I know I am not using the correct terms, but the 'first' pipe coming off the cylinder head (the bent purple one) stays reasonably cool. It is the 'second' pipe leading to the 'muffler' that gets hot enough to boil water when dribbled on it. I don't remember it ever getting that hot before. As before, when I idled back to the dock (about a 10 minute ride through the whole marina) the engine was pretty cool when I got back. I could place my hand on any part of it.

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I was able to find the cooling diagram. The part I repaired is actually the tuned pipe. The area that is overheating is the exhaust manifold.

From what I can gather from the diagram (for some reason in the manual I have that page is in French?!) the only water that comes through the exhaust manifold is coming via the water control valve through the tiny little hose. That doesnt seem right. Is water also coming through the tuned pipe? If not, where does the water from the tuned pipe go? I will attempt to post the photo of the diagram I have. Learned a bit more, but still questions. OK so today I pulled the tuned pipe off to check if water is flowing through it.

I hooked it up to a hose and water flows just fine. No restrictions.

I also disconnected every hose I could find or get to and all were clear. I even pulled the hose from the pump outlet and water flowed from the nipple so no obstructions there. I pulled the tiny hoses from the water control valve (which I reset to default setting as per the manual) and water flows from the little hose that would normally inject into the exhaust. I cannot imagine that provides much cooling, but I dont really know. So I am going to go on the assumption that water is flowing through the head and tuned pipe correctly. So why would the exhaust pipe get hot enough to burn the purple paint black? Even when the exhaust was boiling hot, the cylinder head and the tuned pipe were relatively cool to the touch as were all the hoses.

Not sure it matters, but the muffler and the water box are unaffected and never got that hot. Does anyone know how hot the exhaust pipe is supposed to get? I cannot imagine having a very hot pipe only a few short inches from a plastic gas tank is normal.

The last time I ran the boat I only got it up to full RPM a couple of minutes and again noticed the exhaust pipe was hot enough to sizzle water dripped on it. I haven't run it since I put it back together, though. The water from the front of the head that goes into the tuned pipe via the 1/2' hose is what feeds the exhaust mani.

The line form the water control valve (little line) goes to an elbow fitting and injects water into the INSIDE of the pipe to cool the exhaust gases and to keep the short rubber coupler cool where it connects to the water box. If that little line is starved you will discolor the 'stinger' (lower parts of the tuned pipe) and melt the rubber water box coupler.which looks a little lumpy if you ask me.

Which is what they look like when they get too hot. Your exhaust manifold is the whit rounded part that the tuned pipe connects to, that would be discolored.

So, if you really meant the stinger you need to look at the water control valve. If that is blocked, broken or leaking it needs to be replaced.

Here's a better flow pic I snagged on google. Yeah, I knew I had some of the terminology wrong.

Sorry for the confusion. So what RacerXXX said kinda goes along with what I am seeing.that the water regulator valve may be malfunctioning. I did run a garden hose through the stinger and up into the muffler and did not see/feel any obstructions. The rubber pipe is a bit 'lumpy', but seemed solid enough.

I guess I will find out Thursday when I get back to the marina. I HOPE this is the end. Thanks for the input and for putting up with my incorrect laymans terms! What is the best way to replace that coupler?

I couldn't get to the bolts holding the stinger on. They must be hidden under the engine. Is it easier to work 'backwards' from the muffler which seems to have some clamps holding it in place? The coupler looks like 2 inch gas hose. Is it anything special or can one just get hose from the auto parts store?

So how does one test the water regulator valve? The diaphragm seems intact and the piston moves up and down. When I started the engine with the hose off the regulator (the one that goes to the exhaust system) water came out the hose at idle.

As an addendum to the above reply, I took the boat out today and it ran great, except the exhaust stinger pipe got hot enough to boil water after about 2-3 minutes at 5000-6000 rpm. The engine block, head, tuned pipe, and hoses all were relatively cool to the touch. The pee stream is almost horizontal at full RPM, less at idle (and the water coming out is always cool, not warm at all).

I checked my water regulator valve. Don't see any holes, the piston moves freely. At idle, the small hose pees out a pretty good stream (which would go into the lower part of the tuned pipe). Nothing seems to be leaking into the boat at all. FYI, the water in the lake is 60F if that makes any difference. So I have been searching this site for info on how to test or evaluate the water regulator valve.

Everything I can see about it looks fine. I pulled it off the water box (or is that the muffler?) and using breath power I was able to see the switch between air going out the bottom (thus into the muffler) vs going out the little hose (thus going into the tuned pipe) when I moved the piston/diaphragm. Wondering if it is worth spending more $ for a water control valve when mine seems to work OK. Currently the red adjuster is almost to the bottom, maybe one revolution out. From what I have read tonight, most people say 2-3 turns out is best.

Perhaps I am wrong, but that seems like having it cranked down like mine would send more water to the tuned pipe and less to the muffler which is what I would want for maximum cooling. I am not interested in racing or anything, just running the boat around for fun so max RPM isn't a huge concern. I would sacrifice a few mph to cool the pipe more. Assuming the water regulator valve is OK, hoses are not clogged, I am out of ideas. What damage could I do by running all summer with a hot exhaust other than perhaps melting exhaust couplers? How hot is too hot for the boat?

I don't have a really good way to measure temperature of the exhaust except by dribbling water on it. Thanks again.

Update on my boat. I got the coupler changed out. Ran the boat for 15 minutes at various speeds and a few seconds at WOT. Ran just fine. When i stopped after a high speed run and checked the engine compartment the stinger was hot enough to boil spit, but nothing looked out of place.

The hose into the head was cold, the hose coming out was slightly warm. Head and exhaust manifold and tuned pipe warm, but not too hot to touch. So headed back to the marina. When idling through the marina (5 minute run) I started to get a constant low beep from under the dash. If i goosed the throttle it stopped, but then it would start again.

It did this all the way back to my dock. The indicator pee stream was on the whole time. When I checked the engine at the dock, everything felt cool except the stinger pipe. From reading other posts, it sounds like this beep may be an overheat warning, but the head is cool to the touch.

I am assuming that beeper is connected to the sensor on the top of the cylinder head? Or is there another sensor I am not finding. I kinda doubt the engine is overheating if I can put my hand on the cylinder head. Update on my boat. I got the coupler changed out.

Ran the boat for 15 minutes at various speeds and a few seconds at WOT. Ran just fine. When i stopped after a high speed run and checked the engine compartment the stinger was hot enough to boil spit, but nothing looked out of place. The hose into the head was cold, the hose coming out was slightly warm.

Head and exhaust manifold and tuned pipe warm, but not too hot to touch. So headed back to the marina. When idling through the marina (5 minute run) I started to get a constant low beep from under the dash. If i goosed the throttle it stopped, but then it would start again.

It did this all the way back to my dock. The indicator pee stream was on the whole time. When I checked the engine at the dock, everything felt cool except the stinger pipe. From reading other posts, it sounds like this beep may be an overheat warning, but the head is cool to the touch.

1997 Seadoo Challenger Service Manual

I am assuming that beeper is connected to the sensor on the top of the cylinder head? Or is there another sensor I am not finding. I kinda doubt the engine is overheating if I can put my hand on the cylinder head. When you say stinger pipe are you refereeing to whole tuned pipe or just the tapered part? I don't know your engine very well.

But the 720 is very similar but not the same sooo. I may be off base. There are 2 sections of the pipe. The first half coming out of the engine. And the second part that attaches to the first part and is more cone shaped. If I remember correctly, the first part has water spiraling through passage ways cast into the sides.

The second part just has water poured into the interior and passes out with the exhaust. Which part of your pipe is getting hot? I think they are actually fed from different directions. The first part comes from the top of the engine.

I cannot remember how the second half is fed. Which specific portion is getting hot? Mine boat didn't have one of the water regulator valves so I don't know, but is it possible this is faulty? Also, have you checked to see if the inlet in the engine is clear? Maybe you have a slight obstruction, and it is enough to give you water flow when you are at full throttle but not enough when less water is flowing?

Looking at Racerxxs's picture. I cannot tell where the flush port is.

I know you are not supposed to run the hose without the engine running, but could you take the dark blue line (in the picture) off the water regulator and see if there is resistance pouring water in and see if it sounds like water is running down the tuned pipe? From what your are sayng it really sounds like the problem is between the t-joint coming from the inlet, the water regulator value and the connector going into the last section of tuned pipe. Maybe the hoses on the regulator valve are backwards? Maybe the valve is shot?

The sensor on the top of the motor is the only temp sensor. I was having a weird problem like you and my water regulator 'feeding block' was melted and distorted not allowing proper flow to the jet that injects water into the pipe, I would check the WR really good. If you go to the Seadoo parts link at the top of the page you can see the diagrams and make sure you have all the pieces in there. The jet could be clogged also but none of that explains your temp warning going away with little throttle because of the added flow/pressure coming from the jet pump would increase the cooling through the motor. If you have gas, oil, and the engine is running I'm pretty sure that the only other reason the beeper goes off is for temp.

It seems like you have a blockage some where. All good ideas. I have tried them all. I pulled off every hose and blew through them. I pulled the tuned pipe and hooked up a hose and water flowed easily.

I pulled the small hose to the stinger pipe with the boat running and water is coming out of that. I pulled the WR valve and blew through the hose ports while moving the piston and it seems to work correctly. Also I pulled the hose from the pump inlet which supplies the water in the first place and everything seems ok. Water flows easily through the head too. I think my next step will have to be to try to persuade one of the guys with a similar boat to pull the hose off the stinger pipe to compare their flow with mine. I am all ears to other ideas.