Mysterious sea water leak

[SimonD]

What can cause a sea water leak only at planing speed?

Twin KAD43s on stern drives. I can go at 6 knots all day long with no problem. However even a few minutes at speed results in a lot of water in the sump under the engines. Initially, this was only on the starboard engine, but is now both (a bit worse on the starboard one though). Thinking it was the exhaust, I wrapped paper towel round the flexible exhaust hose, but it stayed dry. I can't see any signs of a leak.

So, is there something on the engine raw water side that only leaks when the compressor or turbo is running or just at high revs? Or is there something that only leaks when the stern is lower in the water on the plane, or taking the engine thrust.

I'm hoping it's one of things that someone with more knowledge than me (that must be nearly everyone) will know immediately what it is. It's driving me nuts as it makes the boat virtually unusable.

 

[Portofino]

Corrosion of the exhaust elbow or horn .
Higher rpm = more water pressure .
Is that additional water when it’s planning hot / warm ?

Or a bellows clip on the has come off something?

 

[BruceK]

Obvious answer would be to look at where the leak is coming from when at speed, or reving in neutral if you can. I'm guessing as the rev's increase so does the raw water pressure as the impeller starts spinning faster. On that basis I would check all hose ends if water is leaking past the circlip and all bungs. There will be a number of raw water brass bungs to drain water. On on a hose alongside the engine, one under the heat exchanger and one under the CAC / intercooler. I have known these bungs to crumble and become the consistency of baked clay. Especially the one under the CAC.

When last did you check the exhaust elbow and clean the coolers. Excess back pressure could be a contributing issue

 

[tico]

Sure it's seawater? not coolant from expansion bottle?
otherwise leaky raw water pump? Joint leaking at high revs/under pressure.

Leak further forward (from anchor locker) that runs back when bow lifts under acceleration?

 

[[2068]]

Is there a drain from "inside the hull void" that flows into the liner underneath the engines?
Ideally you need one person to helm whilst someone else looks into the engine bay to try and see what's going on.

I had something similar with a trim tab leak. The space underneath the engine bay liner was slowly filling up with sea water.
If the cooling system was leaking you'd probably see salty deposits all over the engine, but it's worth checking hoses etc. as above.

 

[SimonD]

Many thanks for the helpful suggestions. Let me reply in order.

Corrosion of exhaust elbow or horn is a possibility and was my favourite until I wrapped paper towel round the hose and found it stayed dry. I guess if might be from further round the bend (so to speak). I'll try more paper towel in obvious places. I don't know if the water was hot/warm. I'll stick my pinky in next time.

The bungs in the drain hoses is an interesting suggestion. I'll have a look at those. The boat was new to me last summer and I haven't checked the exhaust elbow or cleaned the coolers. I'll check the service history again.

It's definitely sea water. I did look at the raw water pump - dry.

A leak from further forward is a possibility, but unlikely. The sumps under the engines are isolated from the rest of the bilge and initially, the problem occurred on the starboard engine only. Ditto a trim tab leak.

I agree that the best way forward is to examine the engines when they're running. The problem is that they're hot with lots of moving parts! It would definitely be safer to do that on the pontoon with the engine in neutral. Is it OK to run these engines at high speed for a few minutes in neutral?

If it helps, the starboard engine, drive and transom shield was removed last autumn for accident repairs. There was a leak from this engine from that point on (previously, it was dry). I initially thought the problem resulted from that work, but now the port engine does the same thing, I'm not so sure.

Final thought: it's a lot of water so you'd think it would be a big hole somewhere and relatively easy to spot...

 

[BruceK]

I think it's one leak worsening and now spraying bridging any gap. If there is blockage anywhere such as exhaust elbow corrosion the higher pressure generated by the raw water pump could be opening up a split hose somewhere and it's spraying ...both sides. I appreciate the KAD300 cooling flow is different to earlier KADS but on my early KAD42's the charge cooler hoses pass behind the engine close to hot exhaust manifolds and turbo's. Changing a oil filter to oil cooler oil hose this weekend had me scrabbling behind that lot noticing not a lot of room and plenty exposed rubbing points. I've noticed on the engine coolant system the pipe from the thermostat housing down to the heat exchanger rubs on a bolt head and it is showing wear there so any rub points on the raw water hoses behind the engine and under the turbo could also be causing this and it's an extremely awkward place to check. However if the amount of water you are receiving is as much as it sounds and it's spraying it should be easy enough to spot without climbing all over the engines while on the plane.

 

[BruceK]

Oh and dont be surprised to find that it's a port engine leak that was spray across to stbd either.

 

[SimonD]

I think it's one leak worsening and now spraying bridging any gap.

That certainly makes sense. The amount of water accumulating under the starboard engine certainly seems to be getting worse. It also seems too a much of a coincidence to get exactly the same symptoms on the port engine after a period of time. Maybe when the engine was moved as noted above, a hose was disturbed and is now rubbing or getting hot as you say.

You're right, it's a very awkward place to check. I've had an idea that might show it up though. I should firstly say that I don't really know what I'm talking about so this might be mad. Would it be possible to disconnect the outlet of the raw water pump and connect it to a tap. Forcing water through the raw water system should create enough pressure to reveal a leak without running the engine. Would I have to disconnect a pipe somewhere before it goes into the exhaust though?

 

[BruceK]

That might work. I have often thought of running my engines on the hard with a hose jammed down into the raw water strainer but always thought better. I have started the engines before without the raw water strainer lid on before (I forget why I think I was being dozy and checking something with the impeller and flow) any way, cut a long story short the water jet that shot out far exceeded my expectations and was far more forceful than any household hose fitting. The engine was only idling but the column of water shot 8 foot up to hit the canvas and then rained down on everybody in a shower.
This was at idle mind. So no, a hose probably wont do it unless you can seal off the other end and pressurise it but I'm not advising that either. Stick to the plan

 

[Portofino]

In general terms it’s best for both exhaust gas + spent cooling seawater to flow simultaneously.
Theres is a risk ( how ever small ) if you elect to run the water , ok fresh not sea by bypassing the sea / raw pump on its own without running the engines ........some water might back flow the wrong way up the exhaust into the exhaust manifold and through a open exhaust valve .....filling up a cylinder .
I,am not overly familiar with the exact nuances of your specific raw water plumbing .You need to be dam sure there is no risk of a hydro lock scenario before embarking on your suggestion.

 

[BruceK]

Porto is right. The water intake to the elbow is below the manifold height but it's always a risk

 

[Portofino]

Suppose he could pull off the pipe from the elbow ......run it in a bucket .
But I doubt a tap will replicate the impeller pressure @3200 rpm engine speed anyhow .

 

[BruceK]

Not based on my empirical experience at ~900 no.

 

[SimonD]

Fair enough. I know a daft idea when I have one! (It's somewhat disturbing that I have more of them as I get older...)

 

[Orthop]

Simon if you didn't found the problem already please let me know of you have interceptor trim tabs...

 

[Mr Googler]

Power steering cooler?

 

[Orthop]

I heart from an water ingress with interceptor tabs only during planing speed, while the blades are extended. This could be one reason why there is no water inside by cruising at 6kn. The blades are retracted and might tighten the gap where the blades are.

 

[SimonD]

They are Lenco trim tabs. I think that means they're mounted externally with no obvious source of leakage.

I didn't realise there was a steering pump cooler. If there is, it would be on the starboard engine, so worth a look.

I've got an engineer coming out with me on Wednesday to have a look round while we're on the plane. He says he'll use an endoscope camera to look round and, hopefully, he'll be able to spot where it's coming in. I'll report back.

 

[Anthonyexmouth]

Something I had a few years ago on an old Ford was a fractured core in the heat exchanger. Similar symptom, idle on the landing stage and all was fine, cruising and the bilge was filling up, i had a silicone tube from the header tank filler overflow into the bilge so when looking for the problem there was no noticeable flow of water as it was hidden away.
Check the header tank for salt water.