1997 Kawasaki 750 STS running hot......help!

[Goodvalue]

Hello and thanks for looking at my problem.
I'm an experienced car builder but this is my first Waverunner.
I just got this 97 STS. It had not been run in over a year and the gas tank was nearly empty but the oil tank was about 3/4 full. I put about 4 gal premium in it.
Took it out for a test run. She started right up and then stalled 3 times while I played on the learning curve. Finally warmed up and I was able to open the choke fully. I ran it for about 5 minutes at moderate throttle and then it began hissing steam out the starboard side water outlet when I backed off on the throttle. Under acceleration the water seemed to flow fine from the outlet but not at idle......steam. The temperature light came on so I immediately headed for the dock and took it home.
At home I attached a hose to the flush system and turned on the water. It runs water just fine out the starboard port, exhaust and the impeller discharge. Knowing engines, I know overheating could be caused by any number of mechanical problems but since I have no experience with Waverunners, I was wondering if the problem was something I did or didn't do?
Any suggestions?
BTW, I have not purchased a manual yet.
Thanks for responding - Roy

 

[bently]

Re: 1997 Kawasaki 750 STS running hot......help!

sounds like there maybe some blockage in the cooling hoses and possibly sand in the water passages thru the engin. You should start with the hoses at the pump and work towards the engine, then disassembly the exhaust to the manifold. Once all that is checked out, look a the water passages in the exhaust manifold for sand deposits and they will settle in the bottom and slow or clog the water flow.

 

[keith2k455]

Re: 1997 Kawasaki 750 STS running hot......help!

On my '98 STX, there are 2 pick ups on the bottom of the boat for cooling water intake...they're supposed to be cleaned yearly, I would start there. They aren't the easiest to get to on my STX

 

[Goodvalue]

Re: 1997 Kawasaki 750 STS running hot......help!



Hey Bently
It appears from these photos that your suggestion of sand clogged exhaust cooling passages was SPOT ON!
As you can see ( if I uploaded these pictures correctly) the passages were about 50% clogged with sand. I was able to clear them with a stiff wire in a large bucket of water.
I included a photo of the metal gasket between the bottom of the exhaust header and the "expansion pipe" if that is what it's called. This gasket blows my mind. I have torn down many auto engines in my day but have never seen anything like this. All the passage ports from the top of the header to the pipe are blocked by metal with the exception of a tiny **** hole located at about 4 o'clock in the picture. It is beyond me to explain how water from the header passes into the expansion pipe which has matching passages to the exhaust header. Why have matching passages if your intention is to block them? I did purchase the manual which has a diagram of the cooling flow but does not show or explain the design of this gasket.
I'll re-assemble everything and test it again.
One more thing which puzzles me - This Jet Ski has a "Limp Mode" temperature sensor, which if I understand the design correctly, reduces the power to a crawl if a high temperature is reached thereby preventing an over heating event which could damage the engine. So my conclusion is........so many of these machines overheat that they had to design a fail-safe mechanism? This is a poor design which we would never put up with in an automobile.
Just my .02 and 40 years diesel and gas mechanical experience.
Roy

 

[Goodvalue]

Re: 1997 Kawasaki 750 STS running hot......help!

Bently
Sorry, I meant the gasket between the TOP of the exhaust header. Damn site wouldn't let me edit my message.
Thanks again - Roy

 

[bently]

Re: 1997 Kawasaki 750 STS running hot......help!

No problem, the sand gets into jet skis by running them onto the beach and/or idling them in very, very shallow water where the pump is sucking up sand. At idle speed the water flow is not enough to push out the sand and settles to the bottom, once it has settled the water flow will never dislodge the deposits.

 

[Goodvalue]

Re: 1997 Kawasaki 750 STS running hot......help!

Bently
Yes, I can see why running the ski in very shallow water would cause it to suck up sand into the cooling system. Also this Kawasaki was only used in salt water which would add salt to the wet sand forming a glue. The clogs I removed were rock hard. This is no doubt why the manual suggests a fresh water flush after each use and evidently the former owner ignored that caution.
That metal gasket, however, still has me stumped but I will re-assemble it all just the way it was and take it out for a test run.
Thanks for your help - I owe you a beer.
Roy

 

[JASmit]

Re: 1997 Kawasaki 750 STS running hot......help!

I realize this is an old thread but I just took my 1997 900 STX apart and found this same odd gasket with all but a small hole blocked off also. Does anyone know what the reason is for this?? It obviously is there by design but it sure doesn't seem logical to block off 90% of the water passageways and leave only this one small hole open. I sure would like to know why this is before I put mine back together.
Jim

 

[Goodvalue]

Re: 1997 Kawasaki 750 STS running hot......help!

I realize this is an old thread but I just took my 1997 900 STX apart and found this same odd gasket with all but a small hole blocked off also. Does anyone know what the reason is for this?? It obviously is there by design but it sure doesn't seem logical to block off 90% of the water passageways and leave only this one small hole open. I sure would like to know why this is before I put mine back together.
Jim

Hey Jim
Yeah. That is one crazy gasket. Possibly the engine runs too cool without it. Looks like an afterthought by Kawasaki. Be careful to reinstall in the correct orientation. I put mine back exactly how it came off and it works. Cleared my clogs and the ski runs properly now.
Roy

 

[JASmit]

Re: 1997 Kawasaki 750 STS running hot......help!

Thanks Roy - I took mine apart expecting to find clogs like the ones in the photos but those ports were squeaky clean in mine. My "waterbox" the appprox 10" dia by 14" long tank and the small rubber hoses that connect the "U" metal exhaust pipe to the waterbox - seem like they are getting very hot - the straps that hold that waterbox are scorched on the side that goes against the metal. So I took everything apart - checked both pick up tubes back by the jet pump up to the engine with air pressure - and everything seems clear. The only thing I found was some gasket sealant in the small hole in that gasket - making that small hole even smaller. So I cleaned out the gasket sealant and put everything back together and will try it again this weekend and let you know how it goes. This old 900 STX motor seems strong yet - slow by today's machines on the lake - but this motor just seems to keep on humming. I kind of wish it would die so I could get a new sled : )

 

[JASmit]

Re: 1997 Kawasaki 750 STS running hot......help!

Well - I took it out a little over the weekend - enough to say that I think it is still getting hot. I have replaced the two small rubber exhaust hoses and the one big one that comes out of the water box, and those hoses are hot enough I can't keep my hand on them after about 5 min of hard riding. And if I drip water on that metal water box is sizzles. But I guess I don't really know how hot they are supposed to get - maybe this normal??
I even took the hose loose where the coolant water exits the rear of the machine and ran it enough to see and feel hot water coming out so I know there is flow there. And the "pisser" that comes out on the right side in the middle of the ski had good flow when I was running it also. Everything seems to be working right but it still seems very hot to me - seems like I will melt those rubber hoses if I run it hard very long.
Do your hoses and that metal water box get that hot on yours??
Jim

 

[Goodvalue]

Re: 1997 Kawasaki 750 STS running hot......help!

Well - I took it out a little over the weekend - enough to say that I think it is still getting hot. I have replaced the two small rubber exhaust hoses and the one big one that comes out of the water box, and those hoses are hot enough I can't keep my hand on them after about 5 min of hard riding. And if I drip water on that metal water box is sizzles. But I guess I don't really know how hot they are supposed to get - maybe this normal??
I even took the hose loose where the coolant water exits the rear of the machine and ran it enough to see and feel hot water coming out so I know there is flow there. And the "pisser" that comes out on the right side in the middle of the ski had good flow when I was running it also. Everything seems to be working right but it still seems very hot to me - seems like I will melt those rubber hoses if I run it hard very long.
Do your hoses and that metal water box get that hot on yours??
Jim

Jim
I have since sold mine. Yours sounds like it is still not getting good enough flow thru the system. If it's getting that hot, there is something restricting the flow. I would dis-assemble and run small furnace brushes thru each piece. They are long and have small heavy wire brushes on them. You can pick one up at any local plumbing supply. I scrubbed all my passages with them to remove the scale buildup.
Good Luck - Roy

 

[JASmit]

Re: 1997 Kawasaki 750 STS running hot......help!

Roy - one last question that you might be able to help me out with. Do you remember if that cylindrical tank at the back of the ski (the waterbox) - the one that the rubber hoses connect to - is it supposed to have water in the bottom of it?? Mine does not - it is bone dry.
From all the disassembly and checking I have done I know that there are two water cooling systems - one that goes into the jacketed area around the exhaust - and one that dumps right into the exhaust. The one that goes into the jacketed area around the exhaust seems to be working right on mine because I took the hose loose at the back of the ski where that water exits and there was flow there - hot water coming out.
The other system that dumps directly into the exhaust - it seems like that water has to come out with the engine exhaust - and if that is so it seems like there would be some water left in the bottom of the water box which would cool the water box and the hoses. And as I mentioned before my waterbox is bone dry.
So if you remember anything about that please let me know, and thanks for your help!
Jim

 

[Goodvalue]

Re: 1997 Kawasaki 750 STS running hot......help!

Roy - one last question that you might be able to help me out with. Do you remember if that cylindrical tank at the back of the ski (the waterbox) - the one that the rubber hoses connect to - is it supposed to have water in the bottom of it?? Mine does not - it is bone dry.
From all the disassembly and checking I have done I know that there are two water cooling systems - one that goes into the jacketed area around the exhaust - and one that dumps right into the exhaust. The one that goes into the jacketed area around the exhaust seems to be working right on mine because I took the hose loose at the back of the ski where that water exits and there was flow there - hot water coming out.
The other system that dumps directly into the exhaust - it seems like that water has to come out with the engine exhaust - and if that is so it seems like there would be some water left in the bottom of the water box which would cool the water box and the hoses. And as I mentioned before my waterbox is bone dry.
So if you remember anything about that please let me know, and thanks for your help!
Jim

Jim
Yes, I believe there should be flow thru the exhaust - disassemble and check for clogs.
Roy