KAD43 freshwaterpump tricky problem

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A_8

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One of my KAD 43's sometimes overheats at low revs, under 1200rpm's. It started last year and after some investigating I found a small leak between the entry hose and pump, fixed by tightening the hose clam.
All well I thought but the problem comes back every now and then whenever I run at lower revs for for more then 20-30 mins. When it happens there is no water in the seawaterfilter or in the pump but the pump turns.
At higher revs it keeps the temp steady at 82 degrees so there do not seem to be a flow issue.

My thinking have been that the pump draws air somewhere and I have therefore tightened every hose clam I can find but it does not help. There is also no visible leak from the water intake on the outdrives to the pump.

I've changed impellar twice since last year and the engine has about 800hours on it.

Now I really don't know what else to look for and would appriciate any new insight or angle to this problem!

Thanks.
 
If your pump is like the Jabsco/johnson type, then check the deflector plate inside the pump, it should be flattening the lobes as they pass it, When you took out the earlier impellers were they damaged??
 
I take it you mean seawater pump, not fresh water pump. If so, check the whole route of the water from pump to exhaust elbow. My guess would be some build up of scale in the heat exchanger/oil cooler/after cooler. So could be time to clean out your tubes!

Eddie
 
I'm assuming you mean the sea water pump (title?).

I would especially check the external hose from the shield to the drive for leaks / kinks / collapsing hose syndrome. Also, is the pump housing or cover plate worn inside (i.e. does it have the same internal shape / profile as the other one)? Also check the fit / sealing of the top of the sea water filter, although if this were leaking you'd have lots of seawater all over the place at high speed...

dv.
 
I am sure its an airleak problem, as it goes away at higher revs when the pump is sucking more. If it was a restriction it would be worse at higher revs as the engine produces more heat and the lack of flow caused by a restriction would give the opposite symptons i.e. overheating at higher revs, and your temp is spot on for a Volvo at high revs.
I would check the wear plate behind the impellor for excessive clearance between it and the impellor, also the shaft seal behind this plate for wear, leakage, the fact that the filter housing is empty is a ssure sign that its pulling air and not water.
If a hose was collapsing it would collapse at higher speeds more than lower due to increased suction from the pump.
You could try putting a section of clear hose right before the pump to check for airbubbles.
 
Th e pump housing is worn at the back and most dont have a wear plate so its a new pump housing, though I get them skimmed at the back and fit a kit inc wear plate from the TAMD 60 c series pump, if you fit a new impeller it needs to bed itself in to the worn rear housing therefore it takes time to suck water up, I would repair the housing, fit new shaft seals and see what result you get before spending over £400 on a new pump.
 
I had exact same problem with one of my kad43's a couple of years ago. The engine would get hot going up the harbour but would be ok when on the plane. Called sea start as I couldn't find the problem. He changed the impeller (the original looked fine and wasn't very old) and the problem was sorted. Something to do with it not making a tight enough seal inside the pump housing?

It was suggested that dropping some fairy liquid down onto the impeller from the filter housing would confirm whether this was the problem as it would make a better temporary seal and draw the water through? maybe worth trying before replacing the impeller?
 
Sorry about the freshwater title, its obviously the seawater pump.

I have been convinced its a sucking air problem but there should be water leaking out and there are no signs of that. Its completely dry around the engine and in the engine bay.

I actually noticed the coverplate being quite worn, never checked the rear hosing but it may well be the case. Thinking about your respones I remembered when manually filling the pump with water through the filter to get it going again the water would slowly drain...now for this to happen the water must pass through the impellor housing on the sides which would confirm a worn housing problem!?

Would you agree?

Thanks/
 
Had a problem with water flow a few weeks ago.Took all the pipes off in the line one at a time to check for flow and it turns out that the system was sucking air at the jabsco cover plate although all looked fine and dandy no leaks etc . New cover plate and new plate seal solved the problem - three tracing hours work for a five minute repair dammit!
 
Hi, from the description of your problem it appears I have the exact same issue with my kad 43. The engine sometimes overheats at low rev and if I manually put water into the impeller through the filter cap the problem goes away. It almost appeared that I had an air leak some-where!!I'm interested to know if the suggestion above has worked?
 
Hi Brian and welcome to the forum!

In my case it seems it was the lid that had been worn out, I changed per advice in this thread (thanks!) and have done 250nm since then without an incident.
Its easy to spot if there are significant grooves in the lid.
In the future I will turn the lid everytime I change the impellor, this way you never get the lids to wear out in one place.
If this would not have helped my last option was to change the rubber hose between the engine and leg, thinking it been damaged during a pressure wash.

Before getting to this point I had checked and tigtened all the clams following the seawater flow.

Good luck!
 
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