Impeller change- now air locked

J

Jabamusic

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Did an impeller change today (Yanmar 3GM30 Raw) and ended up with a system which refuses to pump water - resulting in an overheat alarm etc.

Any suggestions how to proceed now?

Many thanks

Jaba
 
First thing would be to inspect your impeller again. If it's been dry run for any length of time then it's possibly damaged.

Did you change it because of a problem or just an age thing?

Rgds, John
 
If the pump is above the boat's waterline, ie it has to lift water to prime, then I would first suspect that air is leaking past the pump cover plate. Check the gasket and the tightness of the screws.
If the pump suction is flooded, then I've no suggestions other than making sure that the impeller is rotating.
 
If it has been runnin dry for long enough for the overheat alarm to go off, you might have trashed the impeller - worth checking it again now. IF it's OK, try taking off a hose above it an back-filling the hose, so that water runs down to the vanes. Turn the engine over very slowly to get all the vanes wet. Sometimes, they won't lift when they're dry because they don't make a good enough seal against the wall and end cover of the housing.
 
Lubricate the vanes of the impeller with washing-up liquid when you refit it.

You did open the seacock again? !
 
Most are self-priming, but do not take kindly to being run from bone-dry. If you haven't trashed it already, take NorthUp's advice and lubricate with washing up liquid.
 
Wot Avocet said.

Did the same today on my 1GM10. Fired her up and all seemed well then the alarm sounded. Turned Out to be an airlock. I removed the pipe from the water pump and poured 1/2 pint down the hole. Refitted the pipe and all sorted.
 
New impeller was well lub'd when fitted, but could well be trashed for sure.

The housing is just below the waterline, but is fed from a strainer which is well above and when I cleaned that out today I noticed the the water pressure with the seacock open was sufficient to force water up and into it -therefore I;d have thought enough should have run through to prime the housing- maybe therefore a leak? Will investigate further.

Thanks for the responses; I will also help with the priming next time by back-filling with water to see if that helps.

Oh and yes I did turn on the seacock !! :-)
 
when you pull the impeller, inspect it carefully for any missing pieces of vane. if the impeller is missing vane pieces, it is likely that those pieces traveled out from the water pump and lodged in the entryway to your heat exchanger, this means you will have to pull the hose off where the raw water from the pump enters the ht exchr (as i recall it is at the gear side stern end of the ht exh on the 2 and 3 GMs). remove the end cap (and preserve its gasket VERY carefully and you can re use it with a little gasket sealant to help seat it.) and check for trapped impeller pieces there. to do a first rate job if you are missing vane pieces from your impeller , take off the entire ht exchanger, front and back hoses. shine a light into the ht exh to see what you can see in the tubes.. if you see crud or trapped pieces, rod out each little copper tube to make sure no pieces of vane are stuck in there. before starting such a job be sure to have a gasket sealant to restore the seal on the ht exchg end caps. when you are reassemling the end caps onto teh ht exch, tighten the retaining bolts ery gradually going from #1 to #3 to #2 to #4 . DO NOT tighten 1 bolt all the way down then proceed to the next, or the end caps wont seal properly.

before running your engine make sure your engine oil level is fine, and your antifreeze level is good. loss of even an inch of antifreeze as shown by the antifreeze overflow tank on the 2/3 gm's can cause a hot running engine and an overheat alarm. so always carry enough engine oil and antifreeze to top up your systems.
 
agriff

I have had a similar problem on my yanmar 2YM15 . I suddenly lost the raw water cooling and when I inspected my impeller one of the vanes was missing. I replaced it but could not get a water discharge through exhaust. first step was to disconnect the raw water inlet pipe from the filter bowl and drop it down to ensure you do not have a blocked inlet. If there is no problem then there must be a blockage beyond the filter, and I suspected the missing vane may be lodged somewhere . I disconnected the outlet pipe from the filter and blew fairly firmly down it until I heard a mixture of air/water discharging from the exhaust outlet. It worked, and I assumed that there must have been a fragment lodged in the raw water cooling system between the filter and the exhaust outlet. I was probably lucky, but it's worth a try !
 
Re: impeller

agriff said:
I have had a similar problem on my yanmar 2YM15 . I suddenly lost the raw water cooling and when I inspected my impeller one of the vanes was missing. I replaced it but could not get a water discharge through exhaust. first step was to disconnect the raw water inlet pipe from the filter bowl and drop it down to ensure you do not have a blocked inlet. If there is no problem then there must be a blockage beyond the filter, and I suspected the missing vane may be lodged somewhere . I disconnected the outlet pipe from the filter and blew fairly firmly down it until I heard a mixture of air/water discharging from the exhaust outlet. It worked, and I assumed that there must have been a fragment lodged in the raw water cooling system between the filter and the exhaust outlet. I was probably lucky, but it's worth a try !
Click to expand...
 
Re: impeller

I had same problem and fixed it by closing inlet and flooding inlet pipe from weed trap.the air bubbled out then started engine and opened inlet.this completed the water circuit and is now ok
 
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