Raw water pump failure - Need help

[coloradonautique]

So the weather warms up yesterday and I take a day off to hit the lake. We get out there and cruise for a bit but the engine was having trouble keeping the temp at 160-180. Kept creeping up to 190 at idle. New impeller this spring and I checked for leaks.

Sadly we chose not to ski given the engine trouble and as we were working our way back to the boat ramp, she really started having trouble keeping the temps down.

I suspected that I had installed the impeller wrong or the thermostat was not working properly but was very surprised after getting her home to find the impeller was fine but the raw water pump was not pushing much water if any.

I tried a second impeller (the old one) and got the same results. Pulled the hose at idle and the water barely trickles out of the pump, gave it a quick rev and the flow did not change. Took the pump apart again and looked it over carefully but don't see anything out of ordinary.

What gives? I am at the point of ordering a new complete Sherwood pump to replace it but as an engineer, I am completely baffled as to why the current one won't work? Has anyone else every seen a random raw water pump failure like this, especially when the unit looks fine? They are not that complex of a design. I checked the lines before and after the pump for blockages, everything seems fine.

My feeling is that the pump should be pushing a good amount of water at idle and a ton when the revs are higher. Right now it pushes next to nothing and almost seems to lose prime if it has to pull water up from waterline.

Thanks in advance,

Lorin

[coloradonautique]

RE: Raw water pump failure - Need help

P.S. It is installed in the right direction since it work before and I did not remove the intake/out lines when replacing the impeller. I also doubled checked the direction when I removed it entirely to inspect.

[linebacker55]

RE: Raw water pump failure - Need help

I would first check the raw water strainer to see if it is clogged. I don't know about your boat, but mine is on the front of the engine compartment on the drivers side. A big white thing with hoses going in one side and out the other. Another option, you have a bad gasket somewhere, and it is leaking air in, cause a priming loss. Third, if the pump is belt driven, is the belt tight enough, or is it slipping?

[coloradonautique]

Thanks.

I checked Strainer and it is good. I am going to try feeding the pump directly with a bucket of water and see if it works then. If so, then maybe I just have a clog or air leak around the transmission cooler. Thanks. After looking this pump over several times disassembled, I have to believe it is virtually impossible for it not to work when the impeller is good.

Belts are good and not slipping. Pump is getting good rotation just not pushing water. Another day blown working on the boat instead of skiing behind it. I guess it is just the price we pay! Yellow_Flash_Colorz:

[linebacker55]

I had a similar problem, but mine was due to operator error, not running the engine at a high enough RPM to suck up any water, mine won't suck up any from the fake a lake thing unless >800rpm. But anyway, i figured out my NPSH problem by disconnecting the outlet side of the strainer and putting a hose in and turning it on, then starting the motor, and it worked fine. One other thing, are you absolutely sure you got the right impeller? I got one last year that they said was the right part #, and it was just slightly smaller than the one i took out, so did some checking and sure enough they didn't sell me the right part. How is the key on the pump shaft? If sheared that could cause this problem i think??? Good luck troubleshooting!

[coloradonautique]

HELP HELP HELP - TOTALLY LOST

I don't get it at all. I have eliminated every conceivable variable from the problem. I checked the key, spline and belts, no problems there. I can actually see the impeller spinning like crazy if I look into the output port but still no flow, even if I prime it with a hose or try to suck water up through it (tastes real good). There are no leaks because I can blow into the output port while covering the intake hose with my hand and it pressurizes then holds. Crude test but effective.

My last test had the pump with only an intake hose snaked into the bilge that was filled partially with water. Still no flow, so it has to be the pump. I actually tried the pump reversed just for giggles. Nothing. Cranked the revs to 3000 and got a trickle at best or usually nothing at all.

What gives?

I also noticed after removing the last two impellers that there is some abrasion along one side of each blade. About 1/4 of an inch long from the rounded top down the shaft on every blade. That doesn't seem right to me? Something in the case is off kilter? What could have happened to my pump? I am pretty much down to buying a brand new $300 pump if I cannot figure this out.

Lastly, I am fairly certain the impeller is correct one as I purchased it from White Lake.. but can anyone out there verify I have the correct one.

Boat is a 2001 Air Nautique with the GT-40 engine. Pump is stamped SHERWOOD on the back. Impeller kits I purchased are SHERWOOD 09959K .

Thanks. Any other ideas out there.

Very frustrated :evil: ,

-Lorin

[coloradonautique]

One last thought on this. Could I be assembling the pump itself incorrectly? Three bolts, three locations, only seemed like one orientation that would get the mounting bolts in the right locations for attachment to the motor but who knows. Maybe I am missing something.

Can anyone post photos of an installed GT-40 Sherwood RW pump? How about one uninstalled as well?

Thanks gang,

Lorin

[jhiestand]

I had some problems along these lines with my '94 Sport and they stemmed from my dealer installing the pump backwards, then of course I continued to do the same thing. There's a screw on the pump that should face toward the engine block.

It sounds like that shouldn't be the problem, though, since you never removed the hoses or the pump altogether in the first place and it worked fine before? I couldn't quite follow all the troubleshooting steps you've taken, but if you used the replacement impeller during those steps you may have been dealing with two variables at once. Just a thought.

[linebacker55]

Try this website for detailed how does it go together info. http://www.sherwoodpumps.com/Marine-...us/References/

[rocco]

Raw water pump failure - Need help

Have you ever had the pump off before..and you may have crossed the hoses...........That could happen................

[coloradonautique]

Linebacker.. Thank for the link. That is exactly what I was looking for / needed. I will reference it today against the pump itself.

Rocco,
Nope. The unit never had the hoses off from last fall when it worked until Friday when it did not. I have never needed to take the hoses off when I remove the impeller and therefore don't to avoid ever putting it in backwards. I've replaced the impeller on this style pump dozens of times without a problem (on my 91 SN and now the 01 AN). Something is definitely amiss with the pump itself.

Thanks.

-Lorin

[coloradonautique]

Linebacker,
SCORE!! I owe you big. How bout a free White lake nautique T-shirt for you help.. Yellow_Flash_Colorz: Just tell me where to send it.
After referencing the spec sheet you linked against my pump I found that the spacer plate was missing. Must have fallen out during the disassemble last fall. I found it wedged under the ski pylon in the bilge. Stupid Stupid Stupid! Ugh.
I am certain everything will work top notch once I re-assemble all the lines I tore off yesterday. Thanks so much for the link.
Now my only worry is how much damage was done during the overheat. :???: Especially since it was getting little or no water. I guess I will find out sometime in the future. Not much I can do about it now.

[linebacker55]

Well i am glad you solved your problem and could get back on the water instead of angrily sitting in the driveway, and wasting $300 on a new pump. :cheers:

[Rick]

As Long as you didn't run it to long at 200+degrees there should be little or no damage. On a GT-40 the first thing to go is usually the head gaskets. After running it at normal temp for about 15 min check the oil if its milky you have a problem If not you are probably good to go. Keep in mind that the thermostat is there to keep the system operating at 160. It doesn't even open for a while as the engine warms up.

[hollister]

The GT-40 motor will go in to "stutter mode" (engine runs really rough) when it overheats. This is part of the protection built into the electronic igntion. I had a similar experience on my GT-40 when the dealer put the pump in backwards after an impeller change. (I do all my own work now) We had to run in about 1/2 mile in this mode to make it back to the ramp. The engine is still going strong.

If the engine didn't do this, you most likely never even got it to the temps required for damage.