Impeller heating up?

[areamike]

Hey ya'll...another topic, another day.

Recently, since rebuilding my motor I have been very "in-tune" to everything the motor is going. I guess I am a little gun-shy and want to make sure EVERYTHING is 100% smooth.

What my "issue" is. Soon after starting the motor(cold), if I put my hand on the front of the housing that holds the impeller, it starts getting pretty warm. Then as soon as I think it is what I would call almost TOO Hot, it all of a sudden starts cooling off. It is almost like no water is getting circulated at first or very little, however, I can feel water flowing through the hoses, but the impeller is still heating up pretty hot. Once it starts cooling off, then everything is fine for the remainder of running the motor. Then the next time I start and the motor when it is cold, the same thing over again.

So, is it normal for an impeller to "heat up" tot he point that the motor is almost at operating temperature and then start cooling off or not?

Impeller has been replaced. Old impeller was slightly worn and starting to break down. The same behavior(impeller getting hot) was exhibited with the old impeller as well as the new.

Also, there will be a slight squeaking noise from the raw water pump/impeller when first starting that finally quits once the impeller housing starts cooling off.

Edited October 19, 2007 by areamike

[Bill_AirJunky]

Sounds like the thermostat isn't opening up till it gets warm, which is normal. Do you know what thermostat you put in there? Might be interesting to pull it, stick it in some boiling water & test out what temp it opens.

Also might be interesting to run the motor, know that the impeller housing is hot, stop the motor & open the housing........ is there water in there? Or just pull the hose off the housing while it's running. Just so you know the water is flowing.

[vette-ski]

If your water is flowing correctly, the impeller should be pushing water regardless of the t-stat. It bypasses the stat, goes to the manifolds and out the exhaust. Then when the stat opens it flows through the engine block as well. You should run the boat on a hose and verify you have water coming out the exhaust at cold start. If the bypass is hooked up wrong or blocked, then I guess it's possible that you have no flow through the raw pump until the stat opens. The impeller does rub the inside of the cover plate, so the friction can warm it up. But I would think with sufficient water flow, it should never get "hot". That just doesn't sound normal so I'd make sure your water passages aren't blocked at the t-stat bypass or exhaust manifolds.

[areamike]

Sounds like the thermostat isn't opening up till it gets warm, which is normal. Do you know what thermostat you put in there? Might be interesting to pull it, stick it in some boiling water & test out what temp it opens.

Also might be interesting to run the motor, know that the impeller housing is hot, stop the motor & open the housing........ is there water in there? Or just pull the hose off the housing while it's running. Just so you know the water is flowing.

Do you know the thermostat location off hand? I don't think we replaced a thermostat, just replaced a bunch of sensors.

When I changed impellers I bumped the motor over a couple of times to get the old one out. When doing that, water shot out the housing, so I know water is flowing. I also checked both hoses coming in and out and water flows.

[areamike]

If your water is flowing correctly, the impeller should be pushing water regardless of the t-stat. It bypasses the stat, goes to the manifolds and out the exhaust. Then when the stat opens it flows through the engine block as well. You should run the boat on a hose and verify you have water coming out the exhaust at cold start. If the bypass is hooked up wrong or blocked, then I guess it's possible that you have no flow through the raw pump until the stat opens. The impeller does rub the inside of the cover plate, so the friction can warm it up. But I would think with sufficient water flow, it should never get "hot". That just doesn't sound normal so I'd make sure your water passages aren't blocked at the t-stat bypass or exhaust manifolds.

Even if there were partial blockage, it wouldn't explain why after a few minutes of warming up, the impeller finally cools right off. You can even hear the motor change rev a little.

There's no way to put an impeller in backwards is there? I used a Johnson, which, unlike the Jabsco is open on both ends.

[vette-ski]

Yeah, you can put it in backward. But once you run the engine the blades will get forced back the right direction. What I don't know is when that happens, is there enough room in the pump for the blades to flip without ripping them off. It doesn't matter which end of the impeller you insert first. What matters is the direction the veins lay.

What I was trying to say with the blockage. If the bypass is blocked, the impeller can pull water from the lake but has no where to push it because the bypass is blocked and the stat is closed. Thus it heats up because there is no flow through it. Then when the stat opens at 160, there is now an open passage way for the impeller to push water, you get flow through the pump, and it cools off. The change in engine rpm you hear could be another sign that the stat opens because now the engine circulating pump is doing work too.

That's the theory anyway. The way I would test it would be to run the engine on a hose starting cold. Within maybe 30 seconds or so, you should have water coming out the exhaust. If you don't, something isn't right. It takes a few minutes (at least mine) to get to 160 for the stat to open.

[areamike]

What I was trying to say with the blockage. If the bypass is blocked, the impeller can pull water from the lake but has no where to push it because the bypass is blocked and the stat is closed. Thus it heats up because there is no flow through it. Then when the stat opens at 160, there is now an open passage way for the impeller to push water, you get flow through the pump, and it cools off. The change in engine rpm you hear could be another sign that the stat opens because now the engine circulating pump is doing work too.

That is exactly what it acts like it is doing. Is it normal for the stat to be closed to prevent water flow to the block until it "needs" it? Thus the impeller heating up...I will say that if you shut the motor off, which I did the first time because of excessive heat on the impeller, I went to loosen one of the screws on the housing and it sprayed and bubbled like the water in there was almost boiling. So there was NO flow. Water just sitting in there because of blockage or stat closed.

New stat? Because I'm 99% sure I have no blockage.

[Bill_AirJunky]

Or just pull it out for testing purposes. It should be at the other end of the hose from the pump, on top of the intake manifold. If the impeller stays cool, test the t-stat. If it opens at 160 or 180 or whatever it's rated at, look for other blockage.

[vette-ski]

The stat is in the block on the top front of the intake with the 4 hoses coming off of it. The raw water pump is always supposed to flow water whether the stat is open or closed. Every time you start your engine cold, the stat is closed. This does not sound like a stat problem to me. By design the bypass block is supposed to allow water to flow up and out your exhaust even when the engine is still cold (less than 160).

You said your engine was recenly rebuilt. Who did it, and did they not take apart the bypass block on the manifold? I'm wondering if the wrong gasket was installed in there, thus blocking off the bypass. Or maybe be the stat was installed in the wrong place. There's two places it can be put into the bypass block, but I can't remember which one it is supposed to be in. It probably would cause no harm other than what you are seeing. The exhaust manifolds might run hotter than normal too until the stat opens. You might melt the large coupler hoses off of the manifolds w/ no water. To me, sticking a new stat in there won't solve anything. But I'm pretty sure boiling water in the raw pump is not normal. You might check the impeller to make sure it isn't melting.

[Sunsetter95]

The stat is in the block on the top front of the intake with the 4 hoses coming off of it. The raw water pump is always supposed to flow water whether the stat is open or closed. Every time you start your engine cold, the stat is closed. This does not sound like a stat problem to me. By design the bypass block is supposed to allow water to flow up and out your exhaust even when the engine is still cold (less than 160).

You said your engine was recenly rebuilt. Who did it, and did they not take apart the bypass block on the manifold? I'm wondering if the wrong gasket was installed in there, thus blocking off the bypass. Or maybe be the stat was installed in the wrong place. There's two places it can be put into the bypass block, but I can't remember which one it is supposed to be in. It probably would cause no harm other than what you are seeing. The exhaust manifolds might run hotter than normal too until the stat opens. You might melt the large coupler hoses off of the manifolds w/ no water. To me, sticking a new stat in there won't solve anything. But I'm pretty sure boiling water in the raw pump is not normal. You might check the impeller to make sure it isn't melting.

In the large housing on the top front of the intake manifold is where the thermostat is located. The proper location in that housing is at the top. Also, there should be a plastic piece that holds it in the proper location and the bottom of the stat should toward the intake.

If the rebuilder blocked off the intake bypass holes, you will have a problem. Ask them.

In the day, I always blocked them off to keep the carb cooler, but that was a car, no bypass needed.

Ensure that the trans cooler screen is clear.

If the above checks out, as I did, use your garden hose and ensure all the other hoses are clear.

Is this happening in the lake or using a fake-a-lake

I had an issue with a fake-a-lake connected to mine. I seems that while on the trailer I put the fake-a-lake under the boat over the water intake with the hose connection to one side. The hose connection was partially blocked off on the inside by the water intake shield on the boat. My pump squealed some and the water seem to start boiling in the hoses. I new the impellar was good because this was on a new brass replacement pump from Jabsco. I turned the fake-a-lake so the hose connected from the front and had no other issues.

You should have a 160 or 165 thermostat in you engine also.

[areamike]

In the large housing on the top front of the intake manifold is where the thermostat is located. The proper location in that housing is at the top. Also, there should be a plastic piece that holds it in the proper location and the bottom of the stat should toward the intake.

If the rebuilder blocked off the intake bypass holes, you will have a problem. Ask them.

In the day, I always blocked them off to keep the carb cooler, but that was a car, no bypass needed.

I'll be checking today.

Ensure that the trans cooler screen is clear.

I already have. There were pieces of rubber lodged into the inside edges. About 4 pieces.

If the above checks out, as I did, use your garden hose and ensure all the other hoses are clear.

roger

Is this happening in the lake or using a fake-a-lake

I had an issue with a fake-a-lake connected to mine. I seems that while on the trailer I put the fake-a-lake under the boat over the water intake with the hose connection to one side. The hose connection was partially blocked off on the inside by the water intake shield on the boat. My pump squealed some and the water seem to start boiling in the hoses. I new the impellar was good because this was on a new brass replacement pump from Jabsco. I turned the fake-a-lake so the hose connected from the front and had no other issues.

I have not tried a fake-a-lake. This is on the lake. The intake on the bottom of boat to the hose and through to the raw water pump is all clear. See pic

You should have a 160 or 165 thermostat in you engine also.

I do. It never has gone above 165...[/knocks on wood]

[Sunsetter95]

I have an older Mercruiser so mine is a bit different. I pulled off each hose and ran water through it and any engine component to ensure they were not blocked or restricted. From the outlet of the pump, up and out to the exhaust. Just to make sure.

I also noticed that the hose from the raw water inlet on the bottom of the boat, to the pump inlet had partially collapsed inside the hose, restricting the inlet water. I replaced the hose.

When you hear the "boiling" sound, is it truely boiling, or is it could it be air working its way out?

It seems like you have checked most everything already!

[areamike]

The boiling point of water is only 215 F. So I am pretty sure it is possible that the water in the impeller housing is getting hot enough to boil before the stat finally opens up and everything starts flowing at that point.

My friend looked at it as well and "he thinks" the impeller is rubbing the inside of the housing because maybe it is newer and tighter? I said to him, then why does it all of a sudden cool down once the boat hits operating temp? It's like the water is being sucked in by the impeller, but it is only getting to a certain point of flow and then stopping and waiting on the stat to open. Thus the impeller is just spinning and heating up the water that is not flowing.

I am also getting water out of my exhaust

Edited October 21, 2007 by areamike

[Gordo]

The boiling point of water is only 215 F. So I am pretty sure it is possible that the water in the impeller housing is getting hot enough to boil before the stat finally opens up and everything starts flowing at that point.

My friend looked at it as well and "he thinks" the impeller is rubbing the inside of the housing because maybe it is newer and tighter? I said to him, then why does it all of a sudden cool down once the boat hits operating temp? It's like the water is being sucked in by the impeller, but it is only getting to a certain point of flow and then stopping and waiting on the stat to open. Thus the impeller is just spinning and heating up the water that is not flowing.

I am also getting water out of my exhaust

Another possibility is that you replaced your impeller with one that does not fit. It may be too small in diameter, and that would casue it not to prime for the first minute or two, then when you get underway or run up the engine, its able to suck up enough water to prime. Happens a lot. Check that if its still a problem.

[areamike]

Another possibility is that you replaced your impeller with one that does not fit. It may be too small in diameter, and that would casue it not to prime for the first minute or two, then when you get underway or run up the engine, its able to suck up enough water to prime. Happens a lot. Check that if its still a problem.

Interesting. I wondered the same thing. I bought the impeller from a Malibu dealer. I would hope it would be the right one.

It's a Johnson 09-812B-1

[99response]

Not normal, when I run a boat I always grab the impeller housing to ensure I'm sucking water, should be cool within seconds of startup. If you can run the boat up on the hose with a fake-a-lake, have someone start up the boat and you watch the fake-a-lake from outside the boat. It is very obvious if the boat is pulling water or not, you will see water spewing out from the fake a lake but upon start up the boat should take all that water (none spewing out).

We had some problems last summer with "soft" impellers that were brand new and didn't pull water very well because the rubber was too soft. I would try and get a Johnson impeller, I really believe they are a higher quality than anything else I've seen.

Last thing, you said you found bits of impeller in the tranny cooler, make sure none of those are stuck anywhere in the raw water pump housing, you'll have to pull the impeller to look.

-Chris

[areamike]

Not normal, when I run a boat I always grab the impeller housing to ensure I'm sucking water, should be cool within seconds of startup. If you can run the boat up on the hose with a fake-a-lake, have someone start up the boat and you watch the fake-a-lake from outside the boat. It is very obvious if the boat is pulling water or not, you will see water spewing out from the fake a lake but upon start up the boat should take all that water (none spewing out).

We had some problems last summer with "soft" impellers that were brand new and didn't pull water very well because the rubber was too soft. I would try and get a Johnson impeller, I really believe they are a higher quality than anything else I've seen.

Last thing, you said you found bits of impeller in the tranny cooler, make sure none of those are stuck anywhere in the raw water pump housing, you'll have to pull the impeller to look.

-Chris

It's a Johnson 09-812B-1

I'm gonna spend some time at the dock today again.."looking". I can't get it out of the water..No vehicle ATM, however, I have plenty of room under the boat to where if it is possible I can run some sort of "fake-a-lake" from the lake itself...

[Gordo]

A fake-a-lake has water pressure pushing water into the impeller/raw water pump. That makes it easier for it to prime itself. A boat sitting in the water does not have that pressure, so its harder for it to get water moving. Once you put your boat in gear and start moving forward, the water pick up (which is oriented to the bow) gets water forced up into it. Plus, the engine RPM picks up and therefore the impeller is turning faster - all of which helps prime the raw water pump. Sounds like you know the impeller model for your pump, you now just have to see if thats what is installed!! BTW, if one were changing out impellers, I would highly recommend changing to the Globe, blue "Run Dry" impeller. For maybe a couple of bucks more that the Johnson impeller you bought, the Globe will last MUCH longer. Its made out of propylene (not rubber), and will withstand being run dry - they say for 15 minutes, but I have never tried that I have run a Globe for the last 3 years and expect it to go another couple. With a VLX, its a major effort to change impellers !!!

Edited October 23, 2007 by Gordo

[D-GOOSE]

Not normal, when I run a boat I always grab the impeller housing to ensure I'm sucking water, should be cool within seconds of startup. If you can run the boat up on the hose with a fake-a-lake, have someone start up the boat and you watch the fake-a-lake from outside the boat. It is very obvious if the boat is pulling water or not, you will see water spewing out from the fake a lake but upon start up the boat should take all that water (none spewing out).

We had some problems last summer with "soft" impellers that were brand new and didn't pull water very well because the rubber was too soft. I would try and get a Johnson impeller, I really believe they are a higher quality than anything else I've seen.

Last thing, you said you found bits of impeller in the tranny cooler, make sure none of those are stuck anywhere in the raw water pump housing, you'll have to pull the impeller to look.

-Chris

This is the two hugest points where the rubber will be hung up at.

Most Malibus have the Johnson 812b and the Globe cross refer # is 100J and thats the one I'm doing the group buy on and it shouldn't be but a few bucks more then the Johnson.

[areamike]

Another possibility is that you replaced your impeller with one that does not fit. It may be too small in diameter, and that would casue it not to prime for the first minute or two, then when you get underway or run up the engine, its able to suck up enough water to prime. Happens a lot. Check that if its still a problem.

This seems to be exactly what the impeller is doing. If I bump the throttle a little it seems to get the impeller sucking water better. Then all is fine.

It can't be the wrong size. It is the recommended Johnson Impeller. I have a globe impeller. I may take the Johnson Impeller out and try the globe and keep the Johnson as a spare.

[Hwood]

A fake-a-lake has water pressure pushing water into the impeller/raw water pump. That makes it easier for it to prime itself. A boat sitting in the water does not have that pressure, so its harder for it to get water moving. Once you put your boat in gear and start moving forward, the water pick up (which is oriented to the bow) gets water forced up into it. Plus, the engine RPM picks up and therefore the impeller is turning faster - all of which helps prime the raw water pump.

This is where I was thinking the whole time. Do you have a sea strainer? That could be clogged. I also agree you may have a collapsed hose somewhere along the way from the hull to the RWP. You may not be getting enough pressure floating unloaded next to the dock. Jam a garden hose on the other end of the hose that feeds the RWP and tighten with hose clamp. Turn on the water slow to fill the line, start the boat and turn the hose on full.

Supposing everything was put back the way it should be after the rebuild...no need to chase your tail.

A small impeller wouldn't get hot then cool off

Water will flow t-stat open or closed

[areamike]

there was no bolts left over..so I am guessing everything was back together ok...

Seriously though. Yes everything back together ok. No clogging. I ran a fake-a-lake and everything was fine.

I am agreeing with the assumption. So is my only solution to bump the throttle a little after starting?

Edited March 18, 2008 by areamike

[Hwood]

When I put the boat in the water with a dry engine, I try not to let it warm up to long sitting by the dock or on the trailer, get it idling forward to scoop up that water. Most importantly, watch the temp gauge!

[scfdfireman]

Just a quick suggestion, the water pump on a boat is a positive displacement pump. Due to it's close tolerances and rubber impeller it will pump both water AND air (when working properly). Unlike the water pump on your car that's centrifugal, which will only pump water and requires a "prime" if there's air in the system. You may want to check the housing on your pump. If it's scored or scratched it will work at less than optimum, and may have difficulty pushing the air out and sucking the water in. Therefore, the way that you described it finally working after rev it up sounds like a reduced flow or lack of pumping ability.

[areamike]

Just a quick suggestion, the water pump on a boat is a positive displacement pump. Due to it's close tolerances and rubber impeller it will pump both water AND air (when working properly). Unlike the water pump on your car that's centrifugal, which will only pump water and requires a "prime" if there's air in the system. You may want to check the housing on your pump. If it's scored or scratched it will work at less than optimum, and may have difficulty pushing the air out and sucking the water in. Therefore, the way that you described it finally working after rev it up sounds like a reduced flow or lack of pumping ability.

Great advice! I will plan to look more closely at the water pump and housing.

Thanks again.