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98 Ski Nautique


Skihack
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Impeller replaced last year. Just found out from Vince at Discount Inboard Marine that when you disconnect hose from thermostat housing that goes to raw water pump and point it into a 5 gallon bucket, it should fill the bucket up in 15 seconds at 3000 rpm's. Be careful not to let the water coming out of the bypass in the thermostat housing burn you if the motor is hot. I am now thinking my problem is from the pickup/strainer area through the tranny water cooler hose. I am betting some kind of blockage as my impeller and strainer looks good. Thanks.
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First thing is that it is not recommended to run your raw water cooled motor for more than 30 seconds without water at 1000 rpm. So, most people use a 15 sec test and multiply.

Second, what @ DW said about going to your pumps manufacturer and looking for specs.

Most of our pumps will put out around 6-8 gpm at 1000 rpm, and around 20-30 gal at 3500 up. I've seen recommendations by some of the race boat builders that for ultimate engine life and durability you need about 8-9 gpm for every 100hp produced but there's a lot of variables as water temperature etc..

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You probably did this but I'll say it anyway...remove and examine the intake screen/filter on the back left side of the motor. Mine was full of weed desbris recently and we started heating up. Cleared it and back to just under 160 degrees at all times.
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Had already checked the strainer and you can see water going through it with motor running. I didn't think to check tranny water cooler hose as I couldn't really see that something to get in there, but I am going to check anyway. It is the only explanation considering the impeller is new and in good shape.
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Well now I dont feel so dumb. Thought @6balls was talking about something other than the strainer. Mines running fine as well. There is another recent post talking about this and there was about a half a dozen thoughts on what could cause restrictions in water flow. My plan is the same.. tranny water cooler screen next... Anyone have a pic of that. Instructions for checking were on the other thread. Maybe someone could post a link to that thread here. Was kind of a thread hijack so not sure what the title was but I know I had a laundry list of things I needed to check for water flow issues.
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I had an unusual water pump experience on my 2001 Nautique. Upon testing at the beginning of the season, the impeller would not properly draw water from a bucket full of water. Headers would begin to overheat. I removed the impeller and it appeared fine, reinstalled pump....same issue. Complete rebuild kit installed, new impeller new o ring, new brass plate, everything works like it should. Perhaps a test to consider.... remove the raw water intake hose by the transmission, stick a garden hose into the intake hose and run the boat..... if your headers are cool and temps ok, I doubt there is a blockage. Next, stick the raw water intake hose into a bucket that you are filling with a garden hose.... run the motor, you should feel strong suction at the intake hose end, headers should remain cool.... if not, and all of your hose connections are tight, try a full pump rebuild kit. Good luck, there is an answer.
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Do take off and look at the strainer, though, rather than just seeing that there is water flow through through the clear plastic housing while the motor is running. Mine looked like water was flowing and obviously some was because I wasn't totally overheating. After taking it off there was so much weed plugged in the middle of there I can't believe I was getting any flow.
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@skimech. I just went through this yesterday. The seal in the raw water pump was bad causing 2 problems. 1 the water seeping caused the bearings to go bad and 2 the seal being bad allowed the the pump to suck air.

 

I had gone as far as to completely remove the thermostat with no help. After rebuilding the pump it runs 155 all the time. Btw it was a 97 Nautique.

 

 

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Have you added any hardware (shower/heater) to the boat and noticed the change after that? Either of those components might be drawing off some of the cooling water if plumped a certain way.

 

Trans cooler is a prime location for broken impeller parts, weeds, debris to gather. Have you looked at the housing to the raw water pump, I had a plastic aftermarket (read cheap Chinese I assume) (for a Jabsco pump) exhibit a lot of abrasion wear in a short period of time and no impeller damage so it was getting plenty of water. The boat exhibited the same characteristics as the water warmed up. One theory I have is our lake has a new weed species and I am wondering if it happens to be more abrasive on the pump body. The raw water pump is pretty much ahead of the strainer so the debris goes through the pump on most boats.

 

I have simply changed impellers on occasion and solved that very problem. As I was thinking about the test, one element not represented in the test is any backpressure. Backpressure could cause the pump to bleed off water so the test may not tell the whole story.

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New boats are so cool!

 

I have just taken the transmission coolers off and hosed them out. Actually if I'm lazy, I disconnect just the water lines and run the hose backwards through the cooler. The removal had to happen when I had no city water to pressurize backwards. The hydraulic hoses are usually long enough to offer enough working room. Look through the cooler and you should be able to see if it is clear. If it is really gummed up a bit of welding rod pushed backwards carefully should open it up. Caution, I don't know if all coolers are straight through - if it's not the welding rod will damage things. The coolers I've cleaned out were straight through and didn't take much to clean out.

 

My older boats would only get a couple of impeller replacements before the whole pump would need replacement. That's still several years and the pumps aren't outrageously expensive. It was easier than spending hours troubleshooting, chasing esoteric bearings and seals and rebuilding (I learned this from experience). If a new impeller doesn't help much, change the whole pump. Impellers only last a year or so - even if they look OK. The rubber softens and won't pump effectively.

 

Do make sure your filter is not plugged and in good condition. If your lake is weedy the filter is critical. When I've worked with the boat generating weeds or muck the filter can plug up in hours or minutes. Note, the boat's propellor is a great dredge! I even need to clean the filter on my new boat a lot.

 

Eric

 

 

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@wish I replaced the impeller and thermostat and had the same problem still. I started inspecting the raw pump (housing with pulley that drives the impeller) and saw bearing pieces in the slots. This is somewhat common when the seal goes. There was also some occasional water drips from the housing.

 

Do be sure to check all the lines first! My local dealer had the 2 bearings and seal in stock which was a nice savings over buying a new pump.

 

If you have other questions feel free to email me at nestein@burnsandburns.com for a faster response.

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The easy trans cooler check is to remove the inlet side water hose and simply look in or stick you finger in to the inlet side and remove any debris you feel / see. Simply trace the inlet water hose along from the raw water pump to the cooler.

 

What is the water you ski in like, do you have a lot of weeds, do you get the water inlet near a sandy beach or bottom, that will allow sand to be sucked in and that can grind on the raw water pump housing.

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I've also seen on older motors and that is the block chocked full of rust that has crumbled off the inside or sediment from the lake. It usually fills around the back cylinders first bcause the motor is tilted back. You can pop out the back frost plugs and vacuum out the pieces or sediment. Then buy a rubber frost plug that has a T handle which expands it. Have you checked your compession ? If the motor is gettin tired it'll do what you describe too.
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Ok, changed the impeller today in the Sherwood pump. The thermostat is pulled out currently. Checked the tranny cooler. Took bottom and top hoses off and shined a flashlight through it. Squeaky clean. Water strainer also squeaky clean. No visible leak in engine pump behind pulley wheel. Am at a total loss. Temp issue is a bit better. Guessing replacing yr old impeller helped somewhat and/ or the water temp was cooler today do to recent rains so that may be why it's running 185 and not up to 200. Drops off to 160 while running a skier. Am I right in thinking 185 at idle is still to warm? Friend said pull the top of the manifold riser off to see if water flow is being slowed by rust. Can thet happen? There are rust stains runnig down the manifold but it looks like its been ther a while. Any other suggestions. Did I miss something in this thread?? Thanks guys.

 

97 SN GT40 850hrs

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Just pulled the thermostat cover off and took it to the bench. In the port going to the passenger side manifold it had black crud (maybe melted impeller blade) blocking about 25% of the port. It was not rust as it was all black and had to be scraped out and it crumbled as it fell out. Hoping that was the prob. Will test in a little while. Small port for the most part and for 25% to be blocked I think is a lot. Let's hope.
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Well, after running a half a dozen course passes @34mph it ran 160degrees in the course. After all those passes I idled all the way around the lake (smallish lake). It rose but stayed at 180. Left it sit idling in boat house for 5mn and it stayed 180. That's way better then 200. And the thermostat was back in it during the test. How's 180 degrees sound?? Now there still may be a combination of idling after heavy use with skiers that may make it climb beyond that but so far (if 180 is ok) so good.
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My 99 SN GT40 runs 160-165 when running course and will warmup 5-10 degrees if you go to the dock and idle. If I rev it slightly in neutral, it will cool down to 160-165 after a few seconds.

 

180 sounds a tad high but much better.

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If you have noticed that the boat might be slightly louder than before, check the exhaust manifolds for corrosion. The gaps are thin so some corrosion can reduce the water flow a fair amount.
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@DW and @nate93 thanks the manifold will be first and the raw water pump seal second. Manifold looks easy to check, not so sure I'll tackle the raw water pump on my own. I can tell from the factory paint on the bolts to the pump that it's never been removed. @DW if there is corrosion do I simply clean it out?? If so how And what happens to what gets cleaned out?? Seams like it all would fall back into the system. I love BOS for this very reason.

 

Unessisary boat parts do to misdiagnosed - houndreds. Paying someone else to figure it out houndreds more. Seeking advice from the knowledgeable folks on BOS- PRICELESS!!! thanks guys.

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@Wish. I used a stiff piece of wire (bend end so you can't drop it in hole) and a vacuum to clean out my manifold openings. Same for the rear plugs in engine jacket. For some reason it was always left side of engine on mine.
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@DW @thager So I plan to checking the exhaust manifold next weekend. With regards to the 4 bolts that hold the topside of the manifold on, is there any trick to taking it off. I say this in worry as I do not want to break any of them off. Seams like by now they would have welded themselves on after 850hrs. Any tips or tricks would be much appreciated.
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As thager said, scrape or wire brush and vacuum works. You might want to get some gaskets, if old they will probably need to be replaced. Spray some penetrating oil ahead of time, if they don't come out, use some heat on the manifold (gas torch).
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I had a similar problem a couple of years ago when temp suddenly spiked and I shut down. Idled home at around 180 and ever since then have a louder sounding engine. When I got back to the dock I took apart the water pump and saw it had fallen apart on 1/3 of the vanes. Pieces were missing and I suspect flowed down stream into the engine.

 

Would such a scenario, (piece of rubber going into the water cooling system) cause a potentially fatal blockage? i.e, restrict water flow to the mixing area of the muffler?

I now change impellers every year. Any suggestions on the muffler?

And where's the best place to get a new water pump? (95 Nautique)??

Thanks

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Yes, if you got the muffler quite hot perhaps one of the baffles has broken loose thus not mixing and muffling the noise as well. Remove the muffler and look inside to see if you can see some damage, shake to see if there are parts rattling inside. You can also squeeze on the muffler to see if the resin has been baked, if yes, it will be softer and probably a little crunchy.

 

SkiDim carries marine grade replacement parts, several other sources do the same.

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Have not had the currage to remove the 4 manifold bolts. Bottom line, I have a history of making repairs cost more by doing it myself. I know this is a straight forward check but I fear breaking off a bolt. Not enough experience wrenching on that kind of stuff to know when to much force is being used and to know when to stop before it snaps. Other than some WD40 type stuff pryer to turning them, any suggestions? The boat has reached 190 a couple time but for the most part it has been 160s 170s. I still think there is a flow problem based on what I think is a louder exaust as well the the temp spikes.
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@wish. I don't blame you on the manifold situation. Is there anyone you ski with that has a similar year nautique? If so see if you can borrow their raw pump (one with impeller). It takes about 5 minutes to swap. It is a more common problem and you will know instantly. Our Nautique never gets over 155 since rebuilt it.
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The typical lubricants on the base of the threads such as WD-40, liquid wrench, etc.. Another suggestion is to use an air wrench, the hammering will lessen the chance of breaking the bolt. I do understand, it is a PIA to remove broken bolts.

 

The borrowing of a known good raw water pump is a good idea. A small deterioration in efficiency of the raw water pump can cause the symptom you are describing.

 

Another thinng to check is for any kinked hoses, particularly an inlet hose such as the hose leading in to the raw water pump, any soft hoses that could collapse (inlet hoses should have a spiral wire in them to avoid a collapse)

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