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Raw water cooling problem


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Posting on behalf of a novice boater I tried unsuccessfully to help out with his raw water cooling on a bmc 1.5 today. He ran around in a low pound and sucked a lot of c**p into his filter. Cleaned that out, checked the intake pipe as far as I could and even checked the impeller in the jabsco pump. Can't see any more blockages, but still no water moving round the system. I don't have any experience with raw water cooling. Is there anything else obvious to check? Cheers

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If you could take the cover off the intake filter ( if it is above the waterline) then try blowing down it or sticking a wire down it if its straight, you might shift something like a plastic bag, or a rubber glove from the outside of the boat.

Edited by davidb
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If you could take the cover off the intake filter ( if it is above the waterline) then try blowing down it or sticking a wire down it if its straight, you might shift something like a plastic bag, or a rubber glove from the outside of the boat.

Thanks. I've tried poking down the pipe under the filter with a long stick. Doesn't seem to be anything in there, but I think the intake must go off at an angle under the boat, as I can't poke anything further than about the depth of the base plate. Is this likely to be the case, or do you think I've found my blockage? Didn't want to poke too hard and damage any pipework that might be under the boat

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Was there any muck / sand / silt inside the water pump ?

Were the vanes on the impeller damaged ?

Are you sure that you put the impeller back with the correct direction of rotation (with the blades in the correct orientation) ?

Impeller was pristine, so far as I could see. There was a tiny bit of silt, but no sand/grit.it went back in as it came out. This one will only go in one way

If you can put a water hose down it, and pressurise it whilst holding a wet rag round everything, you might get some movement

Thanks. May try that, but no access to mains water where he is at the moment, so not sure if that will be an option

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Impeller was pristine, so far as I could see. There was a tiny bit of silt, but no sand/grit.it went back in as it came out. This one will only go in one way

 

Thanks. May try that, but no access to mains water where he is at the moment, so not sure if that will be an option

Does he have a water pump and taps onboard?

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Sure does. Don't know if you can attach a hose to any of them though!

I used to unscrew the shower hose, a standard garden hose was a good fit in the fitting. Run hose to engine, insert other end (with wrap of tape 6" up to seal) into inlet pipe, turn on shower, blast off the rubbish.

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Don't know how it is all arranged but try undoing the pipe from the jabsco or the filter, whichever comes first and then lowering the end so that its below water level, water should free flow in and start to sink the boat, if it does then re attach it to the pump before you sink, you then know that there is no blockage there, if it only seeps out then the little grille under the boat is bunged up, if there is a vetus type filter in the circuit make sure the top is air tight, if it is not then the pump will suck air. apart from that you will just have to undo pipes in turn till you find the problem. Oh, and double clip any pipes that could conceivably sink the boat.

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I used to unscrew the shower hose, a standard garden hose was a good fit in the fitting. Run hose to engine, insert other end (with wrap of tape 6" up to seal) into inlet pipe, turn on shower, blast off the rubbish.

 

Here's how I do it. Somewhat ridiculous I know

 

dscf5033.jpg

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I used to unscrew the shower hose, a standard garden hose was a good fit in the fitting. Run hose to engine, insert other end (with wrap of tape 6" up to seal) into inlet pipe, turn on shower, blast off the rubbish.

Good idea. Will give that a go. Thanks

Don't know how it is all arranged but try undoing the pipe from the jabsco or the filter, whichever comes first and then lowering the end so that its below water level, water should free flow in and start to sink the boat, if it does then re attach it to the pump before you sink, you then know that there is no blockage there, if it only seeps out then the little grille under the boat is bunged up, if there is a vetus type filter in the circuit make sure the top is air tight, if it is not then the pump will suck air. apart from that you will just have to undo pipes in turn till you find the problem. Oh, and double clip any pipes that could conceivably sink the boat.

Thanks. Unfortunately (in this situation at least) it's not easy to disconnect anything below the water line, as the pump is fed by a long up-stand pipe welded to the base plate. Probably a good safety feature, but inconvenient in this scenario

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Is this direct raw water cooling where canal water goes through the engine or indirect raw water cooling that uses a heat exchanger? If the latter has the heat exchanger been checked for blockages and cleaned out?

 

Is this a wet or dry exhaust?

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Is this direct raw water cooling where canal water goes through the engine or indirect raw water cooling that uses a heat exchanger? If the latter has the heat exchanger been checked for blockages and cleaned out?

 

Is this a wet or dry exhaust?

It's indirect, with a Bowman heat exchanger, and it looks like a wet exhaust (I haven't seen it working, but the outlet from the heat exchanger seems to join up to the exhaust.) I noticed an exhaust leak when turning the engine over. Could this indicate a blockage here? I assume you need to take the big Bowman joints off each end of the heat exchanger to check for blockages here? I haven't done this yet, so could be well worth a try. Thanks!

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Thanks, yes you would have to take at least the inlet end off the bowman but if you do some of the antifreeze mixture would leak out. A totally blocked heat exchanger is rare but if it has not be regularly cleaned/checked its not impossible. Before taking the end caps off try taking the pipes/hoses off each end and back flushing it as suggested above. Collect what comes out so you can see if how many debris you flushed out.

 

Before you try that consider this. If the exhaust becomes fully or partially blocked the pressure in the exhaust feeds back into the raw water system via the pipe injecting water into the mixing elbow. This is likely to create sufficient pressure to force the Jabsco vanes back away from the pump body do it will not pump. If the boater ran until the engine overheated he may well have burned through the inner skin of the exhaust hose, this can be force down by the exhausts gasses so a flap blocks the exhaust.

 

If I was in your shoes I think I would take the hose off the mixing elbow and run the engine. If water gushes out of the hose then the raw water system would seem to be fine it the exhaust is likely to be blocked.

 

It could be the inner lining or, especially if prior to stopping there was a very much reduced raw water flow, the the exhaust mixing elbow might have scaled up so reducing the bore for exhaust gasses.

 

FWIW As a get you home measure I have taken exhaust hoses off and pulled the damaged inner lining out.

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Shapfell has indirect raw water cooling and I used to have a lot of trouble with blocked inlet grid.

My solution (very Heath Robinson compared to Scholar Gypsy's elegant solution)

is a cheap plastic hand bilge pump (the type that look like an overgrown bicycle pump) and a bowl full of water to back pressure the intake.

It works very well (which is more than can be said for it as a bilge pump)

(At a lift out for repainting I examined the input grid and found it had very small slot openings and opened them all up with a file, since then I have had much less trouble)

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If the raw water filter (I hope there is one) is of the Vetus variety - and many are, then it can be surprisingly tricky to seal it adequately, especially if the rubber seal is past its prime.

The Jabsco doesn't have much suction capability for air. Quite enough when there's plenty of fluid about.

 

Happened to me often.

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If the raw water filter (I hope there is one) is of the Vetus variety - and many are, then it can be surprisingly tricky to seal it adequately, especially if the rubber seal is past its prime.

The Jabsco doesn't have much suction capability for air. Quite enough when there's plenty of fluid about.

 

Happened to me often.

 

Whatever type of inlet !strainer" it gas that would always be my first thought. Sometimes people forget that those with a centre stud and wing nut need some sort of seal under the nut.

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Not ridiculous at all, very neat and practical as I would expect from you.

Phil

 

You may wish to revise your opinion...

 

Here I am scrubbing the roof, using the hose, on Reach Lode this morning. Rather slow journey but well worth it.

 

dscf7676.jpg

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You may wish to revise your opinion...

 

Here I am scrubbing the roof, using the hose, on Reach Lode this morning. Rather slow journey but well worth it.

 

dscf7676.jpg

If your on Reach Load why are you on the roof and not down the weed hatch? judge.gif

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Make sure that the impeller rotate with the engine running,

don't run the impeller dry for long,

open the inlet again if it have been closed.

if cleaning the system with a hose, do it both ways from the impeller.

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You may wish to revise your opinion...

 

Here I am scrubbing the roof, using the hose, on Reach Lode this morning. Rather slow journey but well worth it.

 

dscf7676.jpg

That answers my question about how wide reach Lode is!

 

Dinghy and the outboard for us then!

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I've just been pondering on the value of a lifejacket in that waterway, if you fell off the roof (on either side) you would land on the bank !

If by some chance you did manage to fall in the gap between the side and the bank, when it inflated you might find yourself wedged like a cork unsure.png

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