Water Pump Impeller looks fine but..??

[SAWDOC]

Usually replace the water pump impeller in my Yanmar 2GM every season. This year I took it out it seemed as good as when I had inserted it (all lobes present and correct and flexing nicely on rotation) so i decided to give her another while.

Since then I have had two overheating incidents where the alarm has sounded (both incidents in rough weather with big swell running, lots of heeling) and I have had to shut down the engine. Each time when back on the mooring, looked again at the impeller, & raw water inlet all seemed fine and on engine restart water out the transom once again?
Am i looking at the wrong thing ? Could the problem be with the pump itself or elsewhere?
Any suggestions welcome.

 

[pampas]

Sea suction out of water when heeling?

 

[Shanty]

Once had a water pump impellor that failed because the rubber became unbonded from the brass insert. The impellor looked OK, but the insert could turn inside the rubber body. I confirmed this was the problem by turning the engine over with the water pump cover removed - shaft rotated, but the vanes didn't.

The other possibility to consider is that the cooling water inlet is coming out of the water, and air is being sucked in.

 

[SAWDOC]

Once had a water pump impellor that failed because the rubber became unbonded from the brass insert. The impellor looked OK, but the insert could turn inside the rubber body. I confirmed this was the problem by turning the engine over with the water pump cover removed - shaft rotated, but the vanes didn't.

The other possibility to consider is that the cooling water inlet is coming out of the water, and air is being sucked in.

Thanks for the reply. Your first point does not apply as the engine pumps normally when back on the mooring therefore impeller has to be sound.

Other possibility of cooling water intake coming out of the water I agree is possibly happening. The intake is not very far from the keel so considerable heel would be required but certainly the head of water could be reduced, thereby reducing the flow?

I'm thinking about this - once the intake is submerged again should the cooling water flow through again or does it need a while to get air out of the system and prime itself?

 

[Pye_End]

Heat exchanger, or is it raw water cooled?

 

[agurney]

I've had several of these (Yanmar 1gm, but same parts and system).

1. The impeller looks OK, but with enough torque the brass bush rotates inside the nitrile (or rubber or whatever). Opening the cover and turning the engine manually is OK, but holding a vane gives enough resistance to see that there's a problem.

2. cavitation, from sucking air when heeling, but that sorts itself out on the level or on a different tack.

3. bunged up pipe above the water pump restricting water flow - easily checked.

4. impeller looks OK, but actually one of the vanes is cracked at the base so it appears to work at idle, or when urned by hand, but does b*gg*r all under load.

The following are guaranteed a temperature warning:

1. Using the engine while heeled for an extended period. Usually OK after returning to the level.

2. Rapid increase in revs. Shears the brass bush from the impeller and requires a replacement (drying and repairing with epoxy gives a decent spare)


Alisdair

 

[andygc]

Thanks for the reply. Your first point does not apply as the engine pumps normally when back on the mooring therefore impeller has to be sound.

Not so. A disbonded Yanmar impeller will pump water quite contentedly back on the mooring at low revs. The slip starts when the pump is working harder at higher revs. Can't be sure about the 2GM as I have never had one, but certainly the case with two of the impellers I threw away when I had a 1GM. The overheating started some time after starting the engine.

However, given your description, of rough and lots of heeling, is it likely that your intake was out of the water?

 

[dehlerman]

We had intermittent overheating on our GM20 for about 2yrs. Did every check, all ckd out OK. Problem solved when antifouling. A small crab had taken up residence inside the cooling inlet screen and as it grew, it intermittently restricted the cooling water flow to the impeller. Can't imagine how it survived but end-of-problem that day!

 

[Twister_Ken]

Replacing the impeller would be my first move. In fact, I'd have done it anyway at the beginning of the season. Cheap, compared with a cooked engine.

 

[MrCramp]

Thanks for the reply. Your first point does not apply as the engine pumps normally when back on the mooring therefore impeller has to be sound.

Had a 2GM20 and had an identical problem.

Yanmar (or whoever makes the impellor) did make a bad batch where the debonding described by others does happen and I would changs the impellor in your case. Keep the old one on case it does not cure the problem. I am sure I read somewhere thet they are meant to last for at least 5,000 hours.

That pump goes at something like 10,000 revs per minute and any slight loss of suction has a massive effect. I found the end plate (bit you take off to replace impellor) was worn. It had circular lines in it. You can get these removed by any engineering shop useing a lathe. Alternatively you can buy a new one. If the pump is very worn there will be lines in the base of the pump and if that is the case they need removing, if possible, or the pump body replacing. Sailing on the East Coast doesn't help as the water is muddy and causes premature wear of the pump.

Another cause of loss of water is some of the pipes being old and delaminating or being "sucked close" because the walls collapse.

My bet would be a worn pump. I woud be gratefull if you will let us know what solves the problem.

 

[vyv_cox]

That pump goes at something like 10,000 revs per minute and any slight loss of suction has a massive effect. I found the end plate (bit you take off to replace impellor) was worn. It had circular lines in it. You can get these removed by any engineering shop useing a lathe. Alternatively you can buy a new one. If the pump is very worn there will be lines in the base of the pump and if that is the case they need removing, if possible, or the pump body replacing. Sailing on the East Coast doesn't help as the water is muddy and causes premature wear of the pump.

Not sure about the 10,000 rpm (the pulley on my water pump is bigger than the one on the crankshaft, so the pump is doing less than engine revs) but I do believe this to be the correct analysis. After sailing in boisterous conditions the water in the suction hose of my 3GM30 tends to drain back into the sea. On starting the engine it will sometimes fail to prime, probably due to some wear of the face plate. I have tried putting a check valve at the seacock but this didn't help. Closing the seacock does but we usually forget to do it. I now keep a bottle of seawater handy to fill the Vetus strainer, which primes the pump and solves the problem instantly.

One answer to the wear is to make an inner plate from thin plastic, the stuff overhead transparencies are made from is ideal. This prevents wear of the brass plate and has better self-lubricating properties.

 

[ianat182]

Think your first check should be the raw water filter;I posted about this on Scuttlebutt as there is an inundation of weed in our area that in my case took only1/2 hour to 3/4 fill the filter,and its a large one. All due to the recent hot spell with algae and weed; it wouldn't take long to fill.
I assume you were motor sailing your boat. I only have one inlet to the engine - starboard side so am aware of this in similar conditions.

ianat182

 

[MrCramp]

Here is a link to the excellent Yanmar Help site maintained by Marine Power Ltd.

http://www.yanmarhelp.com/1gmwpump.htm

 

[SAWDOC]

A minor eureka moment!

Heat exchanger, or is it raw water cooled?

Raw water cooled.

I had a minor eureka moment driving to work this morning. Mulling over the different suggestions and views, I recalled that when I opened the raw water intake in order to examine the filter, I noticed the water rising to the top of the cylindrical intake ( from say an inch below). Why was it not already at the top? Because of air accumulation! Preventing the raw water from rising as far as the tee piece on the cylindrical intake! My examination of the raw water intake had the unintended consequence of removing the air from the system. So of course the next time I started up the engine she ran perfectly.

Well that's the theory. Next time the engine overheats, I will see if unscrewing the top of the intake solves the problem and if so I will investigate fitting a breather to the intake pipe.

 

[SAWDOC]

Here is a link to the excellent Yanmar Help site maintained by Marine Power Ltd.

http://www.yanmarhelp.com/1gmwpump.htm

Mr Cramp

Thanks for posting the link! That seems to be an excellent guide!

 

[vyv_cox]

Raw water cooled.

I had a minor eureka moment driving to work this morning. Mulling over the different suggestions and views, I recalled that when I opened the raw water intake in order to examine the filter, I noticed the water rising to the top of the cylindrical intake ( from say an inch below). Why was it not already at the top? Because of air accumulation! Preventing the raw water from rising as far as the tee piece on the cylindrical intake! My examination of the raw water intake had the unintended consequence of removing the air from the system. So of course the next time I started up the engine she ran perfectly.

Well that's the theory. Next time the engine overheats, I will see if unscrewing the top of the intake solves the problem and if so I will investigate fitting a breather to the intake pipe.

Sorry, no. Raw water pumps are self-priming (at least, the ones in as-new condition are!) and it doesn't matter if the whole of the suction pipe and strainer are full of air, the pump will draw water through all of it. Otherwise when you launch the boat, or dry out on every tide on bilge keels, you would have to prime the system before starting the engine.

 

[ianat182]

From what you say,is it possible that your water filter(or its piping )is mounted too high above the outside water level and needs to be lowered to match that level when static.

 

[LadyInBed]

Raw water cooled.

You say that you were in rough conditions.

My bet is that air was getting in when your back end lifted so reducing the amount of water round the system and causing the engine to overheat.

 

[fontmell]

impellor

change the impellor every year
1) The compound swells and deteriorates over time making rubber shear from boss extra power needed top drive it and scorring in body on cam and end covers thereby shortening pump life.
2) The impellor in this case has run dry due the rough water therefore the blades become stiff and break off

Jabsco recomend change every year - Replacing impellor annually is a small cost compared to the damage that will occur if engine overheats

 

[SAWDOC]

Sorry, no. Raw water pumps are self-priming (at least, the ones in as-new condition are!) and it doesn't matter if the whole of the suction pipe and strainer are full of air, the pump will draw water through all of it. Otherwise when you launch the boat, or dry out on every tide on bilge keels, you would have to prime the system before starting the engine.

Vyv,
Darn you are 100% correct..there goes my eureka moment!