Intermittent cooling water fault?

[Mirelle]

I have just melted the third Vetus waterlock that I have fitted this season! Given the price of these things and the stench and filth of diesel exhaust down below, I am at my wit's end and would be very grateful for any insight.

Let me describe the symptoms.....

The patient is a Volvo MD2; an ancient but, apart from this business, a healthy little engine. Good compression, starts easily, uses little oil. The cooling water inlet is a Blake 3/4" seacock, well below the waterline, even when heeled. The raw water strainer is the usual Vetus plastic basket job, likewise below the waterline (given the propensity of these things to suck in air), the inlet suction hose is non-crushable type. The water pump, and its impeller, are OK. The thermostat, replaced last year, opens at the correct temperature according to the manual (starts to open at 65deg C, fully open at 78 deg C). There is a syphon break before the water injection bend, which is not obstructed or clogged. I took the heads off and mucked out the water bores in the cylinder heads and manifold last year and they were pretty good at the end of that process.

There is the usual water injection bend and the waterlock is about 15" aft of that, slightly lower; the connection is Vetus exhaust hose.

No trouble until June of this year, since then it has, quite erratically (not always when hot - on two occasions within a few minutes of starting from cold, and on two occasions after a lengthy run, melted the waterlock. I managed a masterpiece of Heath Robinson repair, featuring a yard of duct tape and two Jubilee clips, on one occasion, which is why four mishaps have cost three waterlocks.

On each occasion, when I stopped the engine, it seemed abnormally hot, as if no water had been circulating, yet careful inspection of exhaust hose, turning the engine over on the starter with the decompressors up, showed water coming through.

What on earth is going on? I am completely out of ideas. The volume of water flowing through the engine, when I have my eye on the overboard outlet, does not seem different to the volume going through before.

How can something so simple produce such a baffling (and expensive) problem?

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[StugeronSteve]

Have the overheats been when underway or when tied up?

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[Mirelle]

Under way,each time. On the first two occasions I thought I knew the cause - the first one was motorsailing, before I relocated the inlet strainer from above to below the waterline, and I guessed it had sucked in air. The second occasion was after spending a night aground on soft mud (another story, but basically if you give a guest the helm in an East coast river, keep an eye on where he's going!) and I suspected mud plugging the inlet.

The third occasion was motoring about half a mile to anchor after a long sail, and the fourth was again motor sailing but in about a Force 2 so not heeling. Can offer no explanation for those.

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[StugeronSteve]

Have you tried making her fast to a pontoon and running the engine under load for a good while. That way you can spend more time watching the water outlet and monitoring temperature. Could it be some form of hull fouling that is trailing back and blocking the inlet when underway?

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[Mirelle]

Good thought. I'll try that. I don't think it can be hull fouling as I scrubbed and painted one week before the last three episodes (which happened in quick sucession!) Oddly enough, she motored down to the scrubbing posts (about 8 miles) quite happily despite being very foul....

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[MainlySteam]

<<<"The volume of water flowing through the engine, when I have my eye on the overboard outlet, does not seem different to the volume going through before.">>>

But cannot be so in the few minutes it takes for the damage to occur. It would seem to have to be an intermitent blockage in the cooling circuit pipework or waterways, through a lump or particles of debris picked up with the flow on occasions and causing a restriction but falling away again when the flow is reduced or stopped again. In which case the only solution is to find it. Suggestions:

- at up flow side of the injection nozzle in the water injection bend (possible if scale loosened from the recently cleaned engine waterways has collected there - probably the first place I would look if the injection nozzle presents a restriction after the hose/pipe preceding it)

- delamination inside a rubber hose (including possibility of a delaminated flap on the pressure side of the pump)

- at any other high velocity flow point in the system (constriction), preceded by a lower velocity one where debris can settle

- the 3/4" suction hose between the seacock and strainer, anything sucked into there (if not checked already)

- an air or steam lock (probably unlikely for a new intermittent problem)

Until the intermittent restriction is found the chances of losing the water trap again would seem to be very high.

John




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[Mirelle]

Thanks. Good point. I thought of the water injection bend, which seems OK if I poke a wire through, but will pull each of the hoses off and see that they are clear. I did find a loose lump of scale when I took the thermostat out to check it, so there might be more.

Would it be an idea to take the thermostat out, take the hose off at the pump and back flush the system?

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[dickh]

Mirelle,
Sorry to hear of your problems, may I suggest you remove the exhaust elbow completely and inspect it on the bench - it may be partially blocked - which you won't see when it's still on the engine.
We have just replaced the elbow on my friends boat, it was almost totally blocked with a very hard deposit. With the new elbow the power was restored and the flow of water was almost continuous, much better than before.
I also had this identical problem on my engine two years ago.
They were not Volvo's though, a Perkins Perama & a Nanni.






<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Mirelle]

Dick - thanks - I will do that. Given the age of the elbow, about 12 years, it is more than likely.

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[vyv_cox]

I'm not very familiar with the design of your engine but if it is like most others there are two routes for the water, either through the block or, controlled by thermostat opening, bypassing it. It therefore follows that melting of the exhaust trap must be caused by a failure of the total flow and not by a thermostat or internal engine problem. I suggest you concentrate your attention on the suction side of the pump, the pump itself and the discharge side as far as the point at which it divides. The discharge side, where the two streams rejoin, is also worth checking, which I guess you may have done over the weekend. I have some difficulty in understanding how this one can be intermittent, though.

As others have said, intermittent problems are difficult to find but thoughts such as delaminating hoses, bits of broken pump impeller vanes, air ingress into the pump casing are all worth checking. I would also verify that the siphon trap is working as intended.

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[MainlySteam]

Maybe someone can come up with an alternative diagnosis, but I cannot think of anything except for debris blocking the circuit somewhere.

I am not familiar with the particular engine but having found a piece of scale it would seem appropriate to try and flush the cooling circuit, especially through low velocity places ahead of constrictions, where other pieces may have settled to then be perhaps lifted into the constriction when the engine is run. Especially if you find more scale at the injection point. I know what a pain flushing an engine can be in a boat but it would seem likely to be worth it if it cures what must be turning out to be an expensive and annoying problem.

I don't know how one tells when the problem has been fixed, apart from hopefully finding a very likely cause then waiting and seeing.

Good luck

John

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[Mirelle]

Yes, thermostat operates a bypass. I checked it because I thought one possibility was that it was opening at too high a temperature, suddenly letting boiling water into the exhaust, but this is not so.

Air getting in somewhere - strainer or pump - is a good thought. The syphon trap will be looked at next.

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[frilaens]

I have just checked mine on a 2001 which was overheating. I had already checked for contrictions in the pipes and filter, drained the water via the drain plug with the "sand" that collects there (need to poke a bit with a screwdriver to start the flow) and changed the impellor and thermostat without improvement. In the exhaust elbow I found the inlet from the motor was scaled up, with only half the intended diameter remaining, and the internal channels in the sleeve almost completely blocked. The inlet from the thermostat was OK. After searching the forum I decided to use 30% hydrochloric acid, and dunked it for a couple of hours. This has worked very well and removed most of the scale. I replaced the exhaust hose at the same time as I found it was delaminating; this may have been caused by the excess heat.

Andy

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[dickh]

Perhaps when you have found the problem, it would be prudent to fit an exhaust alarm which will warn you of rising temperature in the exhaust hose. ASAP supplies at Beccles<A target="_blank" HREF=http://www.asapsupplies.com>http://www.asapsupplies.com</A> can supply this, just had a quick look, from £75. - must be cheaper than replacing waterlocks!

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[david_bagshaw]

you havent lost some vanes off the impeller previously, which are now causing the intermittant obstruction?



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<A target="_blank" HREF=http://www.euroboating.net>http://www.euroboating.net</A>

 

[ex-Gladys]

Old rubber coolant hoses can look OK from the outside, but have delaminated and partially collapsed inside... Just a thought...

Larry

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[Mirelle]

Heigh ho! Thanks a lot for that - will do the very same thing, as soon as I can.

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[Mirelle]

Thanks, will do.

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[Mirelle]

Thank you, everyone

for taking the trouble to reply. I will try all the suggestions, in what I hope may be a methodical manner, and report back here after next weekend. Most of the points made were things that I had not thought of.

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[TheBoatman]

Mirelle
I had a similar problem on a Yanmah 30 this year and it turned out to be the Vetus strainer. The dam thing "appeared" to be OK but at certain engine revs/vibrations it would allow air to be sucked in rather than lift raw water. I finally had to change it for a new one but prior to that I sealed the thing down with silicon sealer (paying particular attention to the centre stud) just to be sure that NO air could get in. It worked first time so I changed the strainer - no more probs.
Hope this helps?
Peter

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