MD11 Sea Water Air Lock prob

[LadyStardust]

My MD11c Sea cooled engine has developed a problem that after sailing for a few hours in anything other than smooth waters, there is no water coming out of the exhaust when I start the engine, after much pratting around I have found that if I pull the pipe that feeds water into the pump no water is present, but if I lower the pipe water flows and continues when I connect it back to the water pump. This cures the problem. The Sea water travels from the Inlet/sea cock/strainer to the gearbox and out of the gearbox to the pump. Is it possible I'm getting some kind of airlock in the gearbox or attached pipes? I have checked everything after the pump and it all seems clear. I havent changed anything in this area so I'm a bit confused
Thanks

 

[alb40]

Sound like your pump is worn, and is struggling to rpime properly.

Have you tried a new impeller? Also make sure the pipe doesnt not collapse under suction, causing a blockage.

Failing that, you may find you need to fit a new jabsco to cure the problem.

In the meantime, you could fit a new hose that loops up past the pump, and back down, meaning there will be a small head of water in the pipe when the engine starts, helping the pump to prime.

Hope that helps

Alex

 

[npf1]

also consider changing the raw water pump gaskets/seals as they might be sucking air.

 

[Stemar]

Before changing the pump, look at the condition of the access plate. They do wear, and can then prevent the impellor sealing and therefore self-priming properly. On mine, I cleaned the paint of the outside and fitted it back to front.

If both sides are already knackered, this could be a good time to thing about the cover that comes with knurled nuts so you don't need tools (Speedseal?)

 

[LadyStardust]

My last reply didnt make it to the board! So let me try again.
Thanks for the tips, I now realise that I did in fact replace the impellor and fitted a speedseal cover just before I started having the problems. I now feel confident the problem is due to it not having a perfect seal on the pump. I could only get three of the knurled kknobs to fit because of an obstruction behind the pump, so I used one of the old screws for the 4th. I think I will go back to the old cover now.

 

[DavidGrieves]

Hi

I seem to be going through the same thing. I have an MD11c with an intermittent cooling problem. If I start it on the pontoon it will pick up water and send it out of the exhaust no problems, but after a sail it sometimes won’t pick up water. I have tried all the usual things, new impeller, turned the pump face round (helped for a while), taken hoses off and cleaned and flushed through, but have not cured it completely. I am now thinking the pump is worn and might need a new one. Do I need a new one or can they be repaired in a pump shop?

 

[chrisD]

I had very similar problems with an MD11 and eventually discovered that the exhaust hose internals had overheated and collapsed, resisting the water outflow. Once that was replaced (for just a few pounds) the problem was resolved.

 

[Anonymous]

[ QUOTE ]
I now realise that I did in fact replace the impellor and fitted a speedseal cover just before I started having the problems.

[/ QUOTE ]I had exactly the same problem with the same engine and it flummoxed three professional engineers. When I removed the speedseal and replaced the original cover all was normal again.