WHAT A DAY - MD11LC EXHAUST!

[alisdair4]

What an end to the season! Was motoring 'Drifter a measly 3 miles (Rothesay to Ardmaleish, for the cogniscenti) to be lifted out.

All going well (engine running for about 30 mins at low (12-1500 RPM). Thinks "Plenty of time (I was waiting for the tide) so I'll put the kettle on". No sooner had I thought this than both smoke alarms start sounding, and smoke begins pouring out of main hatch! /forums/images/graemlins/blush.gif

To cut a long story short, I got the boat onto a mooring, killed the engine and, once the smoke had subsided, investigated.

What had happened was that the exhaust anti-syphon device (Vetus Waterlock Type 45) had melted where the exhaust entered it. The exhaust was thus venting directly into the cabin.

Anyway, set sail for the yard, and got hoisted out by the expedient of running the engine for the last 300 yds.

The obvious question is "why". I didn't have much time to check tonight as the yard was closing, but can eliminate the possibility of an intake blockage ( I poured water into the internal sea water strainer, and it drained directly out of the intake valve.)

The next culprit would, presumably, be the water pump, or pump impellor?

 

[VicS]

[ QUOTE ]
The next culprit would, presumably, be the water pump, or pump impeller?

[/ QUOTE ] Yes. but something may have temporarily blocked the intake and fallen away as the boat was lifted.

Now its out you can go through the whole system. Check bit by bit including all the hoses etc and the thermostat bypass and very definitely do not overlook the injection point in the exhaust outlet.

Replace the pump impeller anyway, no sense in boxing it up with an old one in there.

 

[Rabbie]

What a horrible memory of last year that dredged up. Never did find the cause but presume the 'plastic bag' theory of blockage.

 

[alisdair4]

The Plot thickens. I removed the impeller, and checked it. It was OK, although I will replace it later as advised.

I then ran the engine while pouring water into the water intake strainer to see if water came out of the (now completely open) exhaust. It did -which would suggest that the cooling system was working OK. I couldn't run the engine for too long, lest I flooded the cabin with fumes. So the quandary is: do I go ahead and replace the anti-siphon valve and winterise the engine (as it is direct cooled I need to run a lot of fresh water through it, and then run anti-freeze through it). I don't want to risk melting another anti-siphon valve ((95 quids, BTW /forums/images/graemlins/frown.gif)

 

[VicS]

You have confused me a little. We are talking about a water lock, Vetus type 45 you said. That is not the anti-siphon valve. You should also have an anti-siphon valve if the exhaust injection point is not at least 6" above the water line . It will be in the pipe work between the engine itself and the exhaust injection point and should be situated so that it is at least 12" above the water line. If you have one it may too have been affected so should be checked.

You should also inspect and expect to replace the rubber exhaust hoses as they will have been affected by the heat.

I think you should replace any damaged or heat affected bits, rig up a good water supply and give the engine a good run but keep a very close eye on the exhaust to ensure that you do not run dry and burn things up again. I like an overflowing bucket in the cockpit with a hose from there to the hose that is normally connected to the inlet strainer. Stop if water does not come from the exhaust in a reasonable time in the quantity you normally see. (I assume you normally check the water flow from the exhaust after starting the engine.) When you stop be sure to stop the water flow from the bucket before stopping the engine or you will fill the exhaust system simply by siphoning from the bucket.

Regarding winterising the engine the problem is displacing the salt water from the cylinder blocks and getting an anti freeze mixture in them. I think the best procedure is to drain all the salt water via the drain cocks ... both cylinders! .... then run with fresh water as suggested above, if possible open the drain cocks while doing so to ensure all salt is flushed out.

Even if you do that is is difficult to get the antifreeze into the cylinder blocks as even if you put it into the bucket it won't even enter the engine unless the thermostat is open, it just whizzes through the bypass and back out of the exhaust pipe. It can be done by repeatedly draining down via the drain cocks but the best scheme is to collect the water antifreeze mixture leaving the exhaust and return it to the bucket in the cockpit which will now not need a continuous water supply. The smart way of doing it is to rig a small electric pump to return it and the laborious way is to use an additional bucket and return it by hand. If you keep this up until the engine is fully warmed up you then stand a chance of getting antifreeze into all parts of the engine but it is advisable to open the drain cocks until you see antifreeze coming out.

There is some merit in not changing the pump impeller until fitting out time. Two reasons: firstly they are affected slightly by high concentrations of antifreeze and secondly so as not to leave it all "scrunched up" unnecessarily all winter.
Sorry we have now half filled the bilges!

To get back to your actual question. You have got to sort it out now. It may be that you can temporarily bypass the water lock with a plain piece of hose but you need to be certain that your installation won't result in water draining back into the engine as soon as it is stopped. (The boat I used to sail did not originally have a water lock) once you have proved that there is nothing wrong you can fit the new water lock and hoses and proceed with the winterization.

One final thing. You quote the engine as being a MD11LC. Is there something I should have known about the significance of the 'L' before dispensing all this advice?

I hope you can make some sense of all that and that I have not left you completely bewildered

 

[maxi]

Fairly common occurrence is for the water hose between the seacock and the gearbox, to close itself up at operating revs but at low revs the hose reverts to normal - makes diagnosis very difficult. For the sake of a few pence, try putting a new temporary hose in place.

I have had this situation twice with MD11B using Volvo hose.

 

[alisdair4]

Vic,

Thank you for a (very) comprehensive reply! To answer your last question first - the "L" is a gin-induced typo. (Note to self, do not come back from a fun (?) day on the boat, have a large gin and then ask questions of fellow-forumites!).

You are right, I have confused the situation by being a "diesel numpty"! The Vetus 45 is not an anti-siphon valve; however that is what burnt up. The exhaust hoses seemed OK this morning when I checked them. As I have all winter to sort this, it would seem sensible to sort the flushing and antifreeze problem first. It strikes me, if I understand your advice correctly, that I could put a temporary piece of steel pipe (45mm ID) into the gap where the Vetus normally sits, and then go through the procedure you describe. This would avoid the risk of burning up another £95 piece of plastic! The new impeller and new Vetus can be fitted in the spring. Sorry for the confusion, but with as with all new boats, it takes time to recognise what is what. (well, it does me!) /forums/images/graemlins/confused.gif

 

[alisdair4]

Re: WHAT A DAY - MD11C EXHAUST!

Maxi,

In my boat, the input goes from the inlet seacock to a strainer, thence to the gearbox. (I presume this is a fairly standard arrangement). The hoses between the seacock and the strainer and the strainer and the gearbox both appear quite new, and uncompressed. That said, there is little opportunity to test the system under load until next season. /forums/images/graemlins/frown.gif. But I will bear your point in mind then -thanks!

 

[VicS]

[ QUOTE ]
the "L"

[/ QUOTE ] I thought it must have been a misprunt!

Yes use anything handy to bypass the water lock, I had in mind length of hose, domestic waste pipe maybe, but if steel pipe comes to hand then use it. Bear in mind though about being sure that there won't be so much water left in the exhaust system that it will flood back into the engine when it is stopped. Turning off the water flow a bit before shutting the engine down should ensure that it is nearly all safely ejected though.

Your filter? I was thinking of a combined inlet sea-cock (gate valve) with a strainer mounted on top of it but if you have something more fancy mounted near or above the water line then you must check that the top is fitted correctly so that air cannot be drawn in there, but don't over tighten it.

I did mention hoses but the point made later is a very valid one. Also don't forget that the gear box cooler is in that pump suction circuit.