Watermota Sea Panther - raw water circulation problem

[ncritchley]

Hi folks, just wondering if anyone might shed light on this problem. I started my Inboard diesel (Watermota Sea Panther/Westerbeke L25) yesterday, after putting it back in the boat. On the ground in the yard it worked perfectly, sucking in loads of water via the raw water pump, and blowing it out with the exhaust. In the boat afloat however, nothing. Just the usual faint diesel haze from the exhaust, but dry. I've eliminated the following:
inlet in hull - clear
inlet pipe to Jabsco pump - clear
Jabsco pump impellor - rotating correctly when engine is running
pipe from pump to heat exchanger - clear
I thought it might be a draw height issue (can happen when there's a bit of play in these pumps between the impellor fins and the faceplate), so I changed the water supply to a raised tank (clear plastic bottle) above the engine, so some gravity assist. Still nothing. I noticed though that when the engine started, the pump initially sucked some water from the tank, but after a few seconds the water returned, as if there was some kind of back pressure. All this time the impellor was rotating as it should.
The only thing I've done that's different was to blank off the tell-tale feed that comes off the exhaust pipe, as I don't need it. I can't see how this would make a difference (?).
I've attached a picture showing the orientation of the impellor fins. Inlet pipe on the left as you view it, outlet pipe to heat exchanger on the right. Impellor rotation is clockwise.
Very grateful for any insight!
Thanks.
PS: It just occurred to me that I should try disconnecting the pipe that goes to the heat exchanger at the exchanger end. In theory raw water should squirt out when the engine runs .... I think! At least it'll prove that the pump's OK and the problem lies further up the line.

 

[david_bagshaw]

May be the telltale feed relieved backpressure from the exhaust during start up? thus enabling a quick prime?

the other one to look out for is the centre bushing of the impeller spinning around. I have had this happen on a similar sized Jabsco, though I note this is a Johnson pump.

try disconnecting at exhaust water injection point and run the engine,
look for old vanes in the heat exchanger if fitted. along with kinked or collapsed hoses.

hope that helps.

 

[PetiteFleur]

This year when I started the engine afloat, no water was pumped. I filled the inlet pipe from water strainer to pump, well greased the screwed on water strainer lid and it then pumped water through the engine. Been okay ever since. Has happened a couple of times in earlier yrs, make sure the Impeller and strainer has been well greased - I suspect a leaking strainer lid caused the initial problem.

 

[ncritchley]

May be the telltale feed relieved backpressure from the exhaust during start up? thus enabling a quick prime?

the other one to look out for is the centre bushing of the impeller spinning around. I have had this happen on a similar sized Jabsco, though I note this is a Johnson pump.

try disconnecting at exhaust water injection point and run the engine,
look for old vanes in the heat exchanger if fitted. along with kinked or collapsed hoses.

hope that helps.

Thanks David, I'll check what you suggest and report back.

 

[galeus]

I don't know whether you have a pulley driving the pump , if you have I've had the pulley slipping on the shaft (still turning) but not suffciently to drive the pump properly. On another occasion I had a secondary filter in the system that was leaking air into the system causing lack of suction.

 

[ncritchley]

Thanks everyone. In the end I put back the telltale assembly, and sure enough, it worked straight away!