how to fix leaking connection in raw water inlet?

[gordontytler]

I suspect there is an air leak somewhere in the pipework between my sea cock and the raw water pump and I hope to fix this tomorrow.

After the engine has been off for a while I needed to run at high revs to prime the pump again. This was happening each time I went through a lock. One time I forgot and I think now need a new impeller. It no longer primes.

There are about 8 places where rubber pipe connects to the filter, the grear box and some sections of copper tubing.

Is there a quick way to work out where the air is getting in?
Is it a good idea to use plumber's PVA tape on the connections?

It's a Mercruiser/BMW 636.

thanks

 

[David2452]

Finding air leaks (of the vacuum type) can be a real sod, is there any way to pressurise the system and use gas leak detector spray or soap suds? If the connections are taper then some liquid PTFE is a good idea, if they are parallel then they should have some kind of seal of their own, either olives or washers.

 

[kashurst]

it might be worth taking all the pipes off, cleaning everything and looking for cracks and spilts by flexing the rubber hoses etc. How old is the pump itself? eventually the deflector plate wears down or breaks up and you loose suction, or the end plate gets too worn. Maybe consider a rebuild kit for the pump.

 

[gordontytler]

Two excellent suggestions. I have been doing a lot of work on the and suspect that flexing the pipework when removing it could be the cause.

Perhaps I could shut the sea cock and fill the water filter with hot water and effervescant vitamin c pills. I could use my gas leak foam to check the connections.

 

[volvopaul]

Have you replaced the seals inside the pump? If the seal has failed it can allow air in.

 

[superheat6k]

If air is leaking in when the pump is drawing, then expect the residual water in the pipe to leak out when the engine is off, and this might manifest as a furry salty build up. If the leak is below the waterline it wouldn't stop, so wetness would be obvious.

I would try to pressurise with the seacock shut, but is there a possibility you are picking up air underway. In any event the impellor pump is positive displacement, so any air entering would just get pumped through, not make it lose its prime. You mention the impellor is worn, but what about the pump housing or cover plate.

I have a comprehensive parts manual for most Johnson pumps with cross references to many engines. PM me if you would like a Drpbox link to it. I will suggest you make an RNLI donation.

 

[gordontytler]

I am putting all my part number lists and equivalents on my google drive as text documents. It's great for searching on my phone or PC. The pump is this one:-

http://www.jabscoshop.com/marine/pu...ize-flange-mounted-with-32mm-1-hose-ports.htm

The port pump was fine but started spraying last summer. I changed every part with the starboard one and it still sprayed water all over the V-belt. Then I discovered a pin hole in the bronze casting. This is fixed now but the problem of air seeping in started happening after that.

I suspect bending the pipes while removing the pump so many times has caused this. There is also some history, or suspicion of a blockage in the engine on the output side of the pump. I never got to the bottom of that despite pumping chemicals through both engines. Also, perhaps, the inlet is plugged with weed before the filter? If I read my log book there may be some more clues.

I have invited some guests and only have two weekends before I should be heading back to London. Time is limited so tomorrow I will try to

1) get batteries charging and plug in my engine room heaters
2) remove the pump: replace impeller, gasket end plate, shaft seal et cetera
3) visual inspection of pipes - tighten clips, apply plumbers tape
4) fill pipes with water from bottle and attach to pump
5) start engine (I hope)- and if not fixed try the pressure test

Oil change can wait but it will be very cold if I don't fix the Webasto heater.



All your advice is very helpful and much appreciated.

 

[superheat6k]

Possibly bits of rubber from a prior impellor failure jammed in the tubes of a cooler downstream.

Johnson equivalent is part number 10-24127-1

 

[gordontytler]

The old impeller was quite worn from running dry. There were about 10 jubilee clips and some were quite loose. I tightened them all. It's gushing out now, even on tickover. Sometimes you get lucky.

Thanks for the advice.