waterworks problem

[kenp]

My volvo md17c engine refuses to pump sea water through the engine. No water is coming out of the exhaust either at low or high reves. I assumed the impeller was knackered and replaced, however, the old was is not damaged at all. I have tested the themostat and it is working. The pump appears to pushing water up to the thermostat. Between the stat and the exhaust elbow there is an anti sypon valve could this be causing the problem. There is no water getting past this into the exhaust elbow. I ran out of time and could not study this workings of this valve. Can anyone suggest any other reasons for this problem. All help would be appreciated.

 

[Richard10002]

Are you sure it is stopping at the anti-syphon, or could your elbow be blocked?

 

[Danny]

Couldn't just be a blocked inlet or filter could it? The pipework up to the pump and beyond could still be full of water but the pump unable to suck in any more.

 

[TimLamb]

I am no expert, but I had a similar problem, impeller seemed fine but no water coming through.
Changed the impeller and problem solved.
Is the new impeller you have put in definately okay?
Is it worth trying another impeller ? (you could always keep it as a spare if I am talking through my but).
Please let us know when you find the answer to the problem.
Good luck.
TJL

 

[Richard10002]

[ QUOTE ]
Couldn't just be a blocked inlet or filter could it

[/ QUOTE ]

I'm assuming that he has checked the inlet and the filter, and even opened it up to see if water gushes in.

 

[kenp]

I made a mistake talking about an anti syphon valve which in fact forms part of the exhaust system. What i meant was the water is not pumping through a vetus air vent which is between the stat and the exhaust elbow. Vetus website states the vent can block with salt crystals. I will check to see if this could be the cause.

 

[NorthUp]

Another possible failure is the centre brass drive spline in the impeller becoming detached from the rubber vanes, the bonding fails. As Timland says, its worth changing the impeller. You can check if you run the engine briefly with the Pump cover removed.

 

[Bilgediver]

Could you confirm that NO water is coming out of the exhaust at the back of the boat or the antisyphon valve.

If the antisyphon valve is working then water is not supposed to come out of it. However it is supposed to open when the engine stops and break the syphon vacuum that forms ad stop water flowing into the exhaust and messing up the works.

If you read my post on anther similar question then you problem could be the same. The cooling water from the pump and via the gearbox has two paths, one to the engine and on to the thermostat and a parallel path bypassing the engine and straight to the thermostat housing outlet side. This by pass is to cool the exhaust when the thermostat is closed. However it is not unknown for bits of impeller to block the restrictor nozzle where this water enters the bottom of the housing. No water will flow when the thermostat is closed. Just clear the inlet nozzle.

 

[VicS]

Check the inlet, check the hoses for obstruction (partial collapse) gear box is water cooled ... yes? check that's not blocked.

I take it this is directly cooled.

Forget about the thermostat for a moment. Even when it is closed water should flow through the bypass in the thermostat cover and up to the anti syphon valve. Check it is not not blocked

Check the anti syphon valve. Two types made by Vetus. One has a valve that opens to let air in to break the syphon, the other pees water overboard or into a cockpit drain all the time.

Finally check the injection point into the exhaust. .... in fact that could be the sensible thing to start with.

Don't think you can have trouble with the pump impeller spinning on its bush with these. I think the screw that drives it goes though the rubber as well, but check anyway.

(BTW Thermostat should just start to open at the temp specified in the manual)