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addictedoffroad
07-28-2012, 04:23 PM
So, my new to me 81 S&S is eating impellers.

Last trip it ate one. I got lucky and got it off the lake before anything too bad happened. This time I was watching the temp like a hawk. Same thing. Never got it out of the marina.

So, where do I start looking for a blockage? tranny cooler is before the water pump right after it comes through the boat. I started pulling hoses up above and found nothing. Pulled the thermostat housing and nothing there either.

What is really weird is that I tested this new impeller in my driveway with the hose hooked up and it worked fine. Any ideas?

Motor is a 351PCM.

mzimme
07-28-2012, 04:34 PM
Silly question, but gotta get it out of the way. You're not starting it dry are you? Not even for a few seconds? Is there water in the impeller housing when you pull it apart?

addictedoffroad
07-28-2012, 04:48 PM
Silly question, but gotta get it out of the way. You're not starting it dry are you? Not even for a few seconds? Is there water in the impeller housing when you pull it apart?

No, I'm not. Its not started until its in the water. Even testing, I let the hose run for a minute before starting to make sure there is water at the impeller.

Its like its not pumping water. Belt driven pump. With the hose pressure its fine. Without the pressure pushing it, it seems like its not pumping.

addictedoffroad
07-28-2012, 05:01 PM
I just pulled off every hose and cannot find a blockage anywhere.

Water is running free through the system. I cannot figure it out.

LYNRDSKYNRD
07-28-2012, 05:16 PM
Could one of your intake hoses be collapsing when the impeller tries to pull water through

Sent from my ADR6400L using Tapatalk 2

addictedoffroad
07-28-2012, 05:21 PM
Could one of your intake hoses be collapsing when the impeller tries to pull water through

Sent from my ADR6400L using Tapatalk 2

I doubt it. They are all wire lined hoses. Only thing I can think of is maybe the thermostat was stuck closed. But that wouldn't explain the burnt up impeller.

addictedoffroad
07-28-2012, 05:23 PM
I just installed a new impeller. But, I am going to have to replace a few hoses that I cut off to check things out. They needed it anyway. I'm baffled.

I am going to try to put the intake hose into a bucket to see if it sucks up the water next.

Is there anything else I am missing here?

G-Star
07-28-2012, 05:25 PM
A couple of thoughts...

I'm not familiar with your age of boat, but I believe some of the older Nautique 351PCM engines required impellers to be installed a certain direction... if they were installed backwards, they would fail and overheat. Some positive pressure from the hose might allow it to circulate water on land, but not once you dump it in the lake.

Also, how are you hooking up the garden hose to run it out of water? If you're bypassing/disconnecting the section of line that runs from the thru-hull intake to the suction side of the raw water pump, the problem might lie in that section of hose.

Good luck.

Cloaked
07-28-2012, 05:26 PM
Make sure you're getting the housing back on in the correct direction.

You can also have a bearing going out and that could leave a less than proper alignment of the impeller in the housing.

:D

.

G-Star
07-28-2012, 05:29 PM
I just installed a new impeller. But, I am going to have to replace a few hoses that I cut off to check things out. They needed it anyway. I'm baffled.

I am going to try to put the intake hose into a bucket to see if it sucks up the water next.

Is there anything else I am missing here?

Good idea. Remember to keep the bucket at or below the waterline, though. The higher the bucket is, relative to the pump, the easier it will be to draw water from the bucket. If it works at "waterline level", you could drop the bucket down to ground level and see if the pump still pulls water under "worse" conditions.

addictedoffroad
07-28-2012, 05:37 PM
A couple of thoughts...

I'm not familiar with your age of boat, but I believe some of the older Nautique 351PCM engines required impellers to be installed a certain direction... if they were installed backwards, they would fail and overheat. Some positive pressure from the hose might allow it to circulate water on land, but not once you dump it in the lake.

Also, how are you hooking up the garden hose to run it out of water? If you're bypassing/disconnecting the section of line that runs from the thru-hull intake to the suction side of the raw water pump, the problem might lie in that section of hose.

Good luck.

Garden hose is being hooked up right at the point that it comes into the boat. So, I disconnect the intake hose from the Through-hull intake and run it there. Basically "as-if" it were in the lake. So, its not bypassing anything at all.

addictedoffroad
07-28-2012, 05:40 PM
Make sure you're getting the housing back on in the correct direction.

You can also have a bearing going out and that could leave a less than proper alignment of the impeller in the housing.

:D

.

Bearings all feel tight. Yes, that is how it went back together both last time and this time. I scribed marks into it to make sure its aligned right.

addictedoffroad
07-28-2012, 05:42 PM
One question I have is:

Once you launch, is there supposed to be water at the impeller before its actually in the lake? I assume the motor must run a few seconds before pulling the lake water into the impeller.

Cloaked
07-28-2012, 06:12 PM
One question I have is:

Once you launch, is there supposed to be water at the impeller before its actually in the lake? I assume the motor must run a few seconds before pulling the lake water into the impeller.
An age old debate. My take as an enJunere in my non-internet world.......... pumps do not suck, they provide flow. Not for me to debate. I don't care.

Of 33 years of these era boats, I have not had any issues of a slight water deprivation while cranking in the water or running on the trailer with a water feed through the top of the cooler.

I say no to your question... that should not be an issue.

.

macattack
07-28-2012, 06:22 PM
Yes, that is how it went back together both last time and this time. I scribed marks into it to make sure its aligned right.

I believe it is possible to mount the entire impeller housing upside down which will cause your water flow problem; the bucket test will confirm whether the impeller is pulling water through or not; if not, reverse the housing and check it again. Hopefully, someone who has your same boat will provide a pic on how theirs is mounted...

Cloaked
07-28-2012, 06:24 PM
I believe it is possible to mount the entire impeller housing upside down which will cause your water flow problem; the bucket test will confirm whether the impeller is pulling water through or not; if not, reverse the housing and check it again. Hopefully, someone who has your same boat will provide a pic on how theirs is mounted...Did you read anything in this thread? :D

http://www.mastercraft.com/teamtalk/showpost.php?p=863055&postcount=9

.

petermegan
07-28-2012, 06:36 PM
Last trip it ate one. I got lucky and got it off the lake before anything too bad happened[

. This time I was watching the temp like a hawk. Same thing. Never got it out of the marina.

So, where do I start looking for a blockage? tranny cooler is before the water pump right after it comes through the boat. I started pulling hoses up above and found nothing. Pulled the thermostat housing and nothing there either.

What is really weird is that I tested this new impeller in my driveway with the hose hooked up and it worked fine. Any ideas?


Just wondering when you say you pulled hoses above and found nothing, you have checked on the lake side of the tranny cooler and inspected it well for blockages?, I have heard that these pumps do not like restriction on the suction side it can jam the vanes against the housing and destroy the impellor quick smart! I am also a strong advocate of installing the impellor with the vanes in the correct direction and a little bit of lube. When you say you are destroying impellors are you talking of vanes breaking off (They are going somewhere in this case), or are they burnt from lack of water? I still wouldn't trust the hoses and would replace as a precaution in case they are sucking flat inside.

macattack
07-28-2012, 07:37 PM
Did you read anything in this thread? :D

http://www.mastercraft.com/teamtalk/showpost.php?p=863055&postcount=9

.

Didn't realize your '93 pic/impeller housing was the same as an '81:.my bad:D; besides, I'm into my 3rd week with pneumonia and running a fever, not sure what I have read at this point!

Cloaked
07-28-2012, 08:40 PM
Didn't realize your '93 pic/impeller housing was the same as an '81:.my bad:D; besides, I'm into my 3rd week with pneumonia and running a fever, not sure what I have read at this point!That's not a 93 in the picture.

Go back to bed, get rest, stay away from the keyboard, and get well soon.... :D

Just poking fun at you.
.

mzimme
07-30-2012, 12:37 PM
One question I have is:

Once you launch, is there supposed to be water at the impeller before its actually in the lake? I assume the motor must run a few seconds before pulling the lake water into the impeller.

One thing I'v noticed, is that whenever I've had to change an impeller, the impeller housing already had a little bit of leftover water in it that cant drain out when you take the boat out of the water. I think this extra bit of water keeps you from having a "dry start" you're talking about. Having that little water in there to lube the vanes keeps friction low enough for that slight amount of time that the water is being pulled in from the lake. Just my observation, however.

As far as your problem, did you check the thru-hull intake to make sure that was clear of any blockage? Weeds, plastic bags, etc. can get sucked up in there and cause blockage very easily. Might check that out.

addictedoffroad
07-30-2012, 12:41 PM
One thing I'v noticed, is that whenever I've had to change an impeller, the impeller housing already had a little bit of leftover water in it that cant drain out when you take the boat out of the water. I think this extra bit of water keeps you from having a "dry start" you're talking about. Having that little water in there to lube the vanes keeps friction low enough for that slight amount of time that the water is being pulled in from the lake. Just my observation, however.

As far as your problem, did you check the thru-hull intake to make sure that was clear of any blockage? Weeds, plastic bags, etc. can get sucked up in there and cause blockage very easily. Might check that out.

Yes, the intake is clear. I tested both ways with the hose on Saturday. I ordered all new hoses and stuff for it Saturday. I will need to wait until those come in to do the bucket test.

ski_king
07-30-2012, 12:55 PM
Sorry, I am coming into this late.

Remember, it is possible to reassemble the water pump backwards. (I did this once). It wont pump water and the impeller dosn't last long. The when it fails, vaines of the impellar are sent backwards theu the system.

Look at cloaked photo and verify your is put together sae same way. Then take hose off the intake where the water comes into the boat and put in a bucket of water to verify it is pumping in the correct direction.

Doug G
08-01-2012, 10:47 AM
another thought, are you using any petroleum based lubes on the impeller when installing it?

sam196370
08-01-2012, 02:37 PM
I changed my impeller a few weeks ago and think I may need a new one since boat is running fairly hot (180+/-) and it's been run dry a few times when I installed water pump or flush-pro backwards. It was very confusing for me figuring out how it went back together since the screws line up even when it's put together incorrectly.

Kind of a big job but once you're better you may want to pull intake and check water passages in engine/exhaust manifolds. Since it's an older boat they may have build up or other blockages

I thought of putting some grease/oil on impeller when installing a new one; is this a bad idea? Makes sense to me if they burn up quickly without water

jmw
08-01-2012, 02:49 PM
I don’t know see how it's possible on a raw water impeller but I had a vehicle water pump that the impeller which pushes the water through the engine came loose. It looked correct and the shaft was spinning but the since the impeller was loose, no water was being pushed to cool the engine. If you are running the motor with a water hose the pressure from the spigot will push water through the engine and keep it cool. Try placing the hose in a bucket and make the engine suck the water as it does in the lake. If it doesn’t cool you have a blocked line somewhere or the pump is not sucking and pushing the water properly.

SilviaMan
08-01-2012, 03:00 PM
I lube my impeller with dish soap when installing.
If the boat sits a while between outings I'll pop the top hose off and squirt some soap in there too.
I figure the few cranks I give it in the driveway to make sure she'll crank at the lake will move the soap around.
(just as a side note... I squirt some soap on the prop shaft and strut bushing before running on land too)