Baffled by Raw Water Cooling Problem

[sy_gilana]

I think the last two posts might knock it on the head.
My own was to ask if you put the cam back?

[Pgisailor]

You may want to check the raw water impeller cover for a tight seal. I always coat the new seal with scuba dive shop pure silicone grease to insure no air leaks. Good luck.

[sailr69]

I didn't see any reference as to the proper direction for the impeller vanes. hope that is not the issue. just observe what the vanes look like when turning. some common sense here should fix the problem. you are smarter then the pump!

[sailorchic34]

One other note is to check that the raw water strainer is flooded. Mine got air bound one time.

[um saudade]

OK, if the hoses are not backward then check to see that the cam(shoe) is installed on the correct side of the pump body. The shoe should fit on either side so the pump may be driven in either direction.

Nick has it right. test the pump separate from the system. One step at a time. This pump will pump and pull a good vacuum by just spinning the engine with the starter. No real need to run it, or if you do keep it short!

[Greg Shakeshaft]

Hello again everyone,

well I am pleased to report that my raw water is flowing as it should once again but I am not entirely sure that I know why however......

I took the advice of Chas Erwin and looked at the outlet side of the heat exchanger. By removing the pipe immediately behind the exchanger (that's the pipe that is attached to the union on the heat exchanger casing) and turning the engine over it appears to allow the flow of water through the system and remove any pressure irregularities that the exhaust system may be creating. I must stress that I have no idea why but, as soon as this pipe was removed, water flowed easily through the system. Obviously, my engine bay got wet but the water ran down into the bilge and got pumped away easily. I allowed the engine to idle for about 30 seconds during which time I observed that there was a constant flow of raw water exiting the union at the rear of the heat exchanger. After which, I turned the engine off and replaced the pipe and tightened up the clip. Turning the engine back on I was praying that water would emerge out of the exhaust as it should and I was not disappointed. It poured out and I breathed a BIG sigh of relief. As I said already, I am not at all sure why removing this pipe has solved the problem, but it has. Thankyou one and all. I celebrated by taking her out for a sail although I must admit, I kept one eye on that exhaust the entire time I was exiting and reentering the harbour

I was only at peace when the sails were up!!!

Cheers.

[cheoah]

Originally Posted by Greg Shakeshaft

Hello again everyone,

well I am pleased to report that my raw water is flowing as it should once again but I am not entirely sure that I know why however......

I took the advice of Chas Erwin and looked at the outlet side of the heat exchanger. By removing the pipe immediately behind the exchanger (that's the pipe that is attached to the union on the heat exchanger casing) and turning the engine over it appears to allow the flow of water through the system and remove any pressure irregularities that the exhaust system may be creating. I must stress that I have no idea why but, as soon as this pipe was removed, water flowed easily through the system. Obviously, my engine bay got wet but the water ran down into the bilge and got pumped away easily. I allowed the engine to idle for about 30 seconds during which time I observed that there was a constant flow of raw water exiting the union at the rear of the heat exchanger. After which, I turned the engine off and replaced the pipe and tightened up the clip. Turning the engine back on I was praying that water would emerge out of the exhaust as it should and I was not disappointed. It poured out and I breathed a BIG sigh of relief. As I said already, I am not at all sure why removing this pipe has solved the problem, but it has. Thankyou one and all. I celebrated by taking her out for a sail although I must admit, I kept one eye on that exhaust the entire time I was exiting and reentering the harbour

I was only at peace when the sails were up!!!

Cheers.

Always satisfying to see water spit out the back after the flow stops. I think the lesson for future troubleshooting is to break it down piece by piece, as other posters suggested. It can be anywhere from the intake seacock through the exhaust system. Always keep an open mind when trouble shooting, as it is easy to say "it was working before" with just about everything, but you just start at the beginning of the system, and work your way through. Pulling pump output and directing into bucket can rule out a lot quickly, like seacock, impeller issues, lack of seal, and strainer clog/air - allowing you direct your attention to the exhaust end. Glad you got it running.

[Therapy]

Nice to hear you got it running but too bad you (we) don't know what the issue was.

Maybe you just dislodged something in the exhaust without noticing.

[Northeaster]

A few years ago, my raw water pump used to loose it's prime, and become "airlocked' from sailing with the seacock open ( I believe from the Venturi effect, as water passed by the hull, and pulled water put of the seacock / hose)
I knew this should not happen, but it did, and I would sometimes have to pull the raw water hose off where it goes into the exhaust elbow (no heat exchanger), which would allow it flow again, and then put it back on and all was well.

Anyway, following advice here, I noticed some scoring of the cover, where the impleller wears against it. Cleaned other side of cover, and installed it backwards, with new surface against impeller (permitable on some pumps). Has worked flawlessly ever since and never have to close the seacock nor pull off hoses now.

I agree with others here that a worn cover has made the pump work at less efficeincy, and it canot always overcome airlocks, etc.