Exhaust elbow.. when to remove and clean?

[Nostrodamus]

On seawater cooled boats the exhaust elbow seems to be one part to keep your eye on.
A friend here has had to sail without an engine for a while as each time he turned it on it quickly overheated. When he took the elbow off it was completely blocked and it took some shifting.
I imagine that a blocked elbow will cause real problems and he was lucky not to damage his engine.
So how often should they be checked or removed for checking.

While we are on the subject do you also remove your non return valve to the engine (those upside down "U" things same as you may find on the toilet pipes. Can they be cleaned or do you replace them. For a bit of plastic they are very expensive.

Thanks for any replies/

 

[nigelmercier]

I would inspect when buying a used boat, and every couple of years.

 

[Appledore]

I would think that it depends a lot on the type of engine and its age. I have a Yanmar 1 GM 10 and I remove the elbow annually, especially to check for internal corrosion which could lead to water entering the cylinder head. My elbow was found to be corroded internally a couple of years ago.

As for the water trap, I have never examined this, but I suppose I ought to do so occasionally!!

 

[vyv_cox]

Very engine dependent and probably also according to how you use it. My Yanmar 3GM30F has the original manifold which has never been off. A couple of weeks ago I removed the exhaust hose for another reason and looked up inside it. I could see no corrosion or deposits. The engine is more than ten years old and has done 2000 hours plus a few.

 

[Tranona]

If you run your engine properly you should not have any trouble with the exhaust. It is lots of slow low load running that causes the problems. The anti syphon valve needs checking and cleaning depending on which type it is. If you have a Volvo one the procedure is in the engine hand book. There are two types of Vetus valve - one is open so you have a constant "pee" overboard so easy to check. If it is the type with a flap valve then you unscrew the top and clean it. Obvious what you need to do when you take the top off (carefully!)

 

[saxonpirate]

A friend here has had to sail without an engine for a while as each time he turned it on it quickly overheated. When he took the elbow off it was completely blocked and it took some shifting. /

And I should imagine that's the only time that engine got hot in its life. Got to agree with Tranona and Vyv here, slow/cool running of yacht engines will lead to soot and coking. Any diesel engine needs to work hard, that's what they're for. When you think of the hours per year a yacht engine does, and compare that with the hours worked by a diesel in a fishing boat you'd expect the fishing boats engine to be clogged solid. They never are though because they are worked hard and hot. Idling and doodling about at a 1000rpm will kill any diesel...

 

[DaveRo]

... Got to agree with Tranona and Vyv here, slow/cool running of yacht engines will lead to soot and coking. Any diesel engine needs to work hard, that's what they're for...

What constitutes slow/cool running? I'm usually happy to achieve 5kts SOG and unless we're powering into waves that's usually 2000-2200 rpm with my Yanmar 3YM30 (Jeanneau SO35). Is that slow/cool?

I'm supposed to inspect the exhaust elbow (it's plastic) annually but so far I've failed to get the pipes off and haven't persisted for fear of breaking something - spares being not readily obtainable at short notice in Greece. (It's 7 years old and done about 850 hrs.)

 

[David2452]

On seawater cooled boats the exhaust elbow seems to be one part to keep your eye on.
A friend here has had to sail without an engine for a while as each time he turned it on it quickly overheated. When he took the elbow off it was completely blocked and it took some shifting.
I imagine that a blocked elbow will cause real problems and he was lucky not to damage his engine.
So how often should they be checked or removed for checking.

While we are on the subject do you also remove your non return valve to the engine (those upside down "U" things same as you may find on the toilet pipes. Can they be cleaned or do you replace them. For a bit of plastic they are very expensive.

Thanks for any replies/

If you check it whilst OK with a cheap laser thermometer and make a note, then it is easy to check temperature increases indicating restricted flow, we used to do it with melt sticks on Mercruiser raw water cooled motors but the cheapness of reliable laser thermometers has made things much simpler.

 

[Tranona]

What constitutes slow/cool running? I'm usually happy to achieve 5kts SOG and unless we're powering into waves that's usually 2000-2200 rpm with my Yanmar 3YM30 (Jeanneau SO35). Is that slow/cool?

I'm supposed to inspect the exhaust elbow (it's plastic) annually but so far I've failed to get the pipes off and haven't persisted for fear of breaking something - spares being not readily obtainable at short notice in Greece. (It's 7 years old and done about 850 hrs.)

That is at the bottom end of the operating range, but you are putting it under load to move the boat. The slow running referred to is either running at tickover or more commonly charging batteries which is not loading the engine. Many sailing boat auxilliaries are run for short periods at the beginning and end of the sail so never get to working temperature.

Are you sure the exhaust elbow is plastic? Think you are referring to the waterlock which is a different thing. The exhaust elbow is on the cylinder head and is either a casting or a steel fabrication.

 

[nigelmercier]

What constitutes slow/cool running?

I suspect my engine is run too slow when my boat partner is on-board, he rarely goes over 1500 RPM. Is there any value in giving it a thrash from time to time? If so, what RPM and duration?

 

[Tranona]

I suspect my engine is run too slow when my boat partner is on-board, he rarely goes over 1500 RPM. Is there any value in giving it a thrash from time to time? If so, what RPM and duration?

Yes. You should run it at between 60 - 70% of max rated revs which on my Volvo 2030 is in the range 2200-2500. Yanmar suggests you give occasional bursts up to maximum revs and this applies to most small modern diesels. The boat should be propped so that this type of revs puts load on the engine and gives a comfortable cruising speed. Again on my boat 2400 gives 5.5 knots in flat water and just over 7 at 3500.

 

[saxonpirate]

I suspect my engine is run too slow when my boat partner is on-board, he rarely goes over 1500 RPM. Is there any value in giving it a thrash from time to time? If so, what RPM and duration?

Most definitely, and more now than again. Regarding revs, I don't know your boat or engine, but if both are in good condition 2500 rpm shouldn't be a problem, or 2750/3000 for that matter. That'll clear the soot Take her to 2000 rpm first, see how she feels and take it from there. You'll also gain more confidence in the engine by pushing it more. Its more a question of getting the engine to work and actually push the boat through the water instead of just tootling over the top of it.

 

[Nostrodamus]

Commonly known as an Italian tune up. Can clear a lot of problems. Trust your engine It will stress you more than it will it.

 

[vyv_cox]

The Yanmar workshop manual recommends full revs, 3600 rpm, for five minutes after every two hours at cruising revs. My normal cruising revs with 3GM30F are 2000 - 2300 but I do the flat out run from time to time, not as often as Yanmar say. I very rarely let the engine tick over or use 1000 - 1800 rpm.

 

[vyv_cox]

Are you sure the exhaust elbow is plastic? Think you are referring to the waterlock which is a different thing. The exhaust elbow is on the cylinder head and is either a casting or a steel fabrication.

Following some recent discussion about Yanmar manifold materials I checked mine with a magnet. It is not attracted, so probably a 300 series stainless steel.

 

[Daydream believer]

As for the water trap, I have never examined this, but I suppose I ought to do so occasionally!!

I have a Volvo 2020MD
I decided to check my vacuum valve after 6 years & replaced the small neoprene disc
The damned thing leaked thereafter - filling a 5 litre container every hour
After numerous attempts to solve this, someone on the forum suggested the unit should not be tightened up too much
That sounded a bit wrong but in exasperation i tried it
I do not know why, but hey presto, the valve now works properly
I still have the outlet hose diverted into the container but i get only a cupful of water every hour of running
So if you are thinking of taking it apart check it is working by putting the hose in a can first. If a small amount of water dribbles through then leave well alone. If no water, or lots, come though then be prepared for hassle. Then only tighten hand tight plus a quarter turn & pray

 

[DaveRo]

...Are you sure the exhaust elbow is plastic? Think you are referring to the waterlock which is a different thing. The exhaust elbow is on the cylinder head and is either a casting or a steel fabrication.

Thanks for that tactful correction. That would be the, er, elbow-shaped steel pipe bolted to the back of the engine with a gasket and having a side-input from the heat-exchanger? It's not labelled on the diagrams in the operating manual; I assumed that was part of the exhaust manifold. I'm glad I asked!

The water-trap thing is not mentioned, but I guess that's not Yanmar's responsibility. The Jeanneau owner's manual is useless.

 

[LONG_KEELER]

Commonly known as an Italian tune up. Can clear a lot of problems. Trust your engine It will stress you more than it will it.

Yes. When the boat speaks to us when over-canvassed so do our engines.

I have a direct cooled diesel . Because of our cold northern waters and British conservatism with throttles, it is not until we have an against wind and tide thrash in the middle of a 3 month heatwave that the engine speaks to us.

I now try to give it a blast whenever I can remember.

I was surprised how narrow the waterways in the Elbow were compared to the exhaust holes when I had it off. Also, there was only a 3mm hole than fed the engine galleries and then to the thermostat ( Volvo 2001 ). I reckon a de-clag every two seasons is about right for me.

 

[nigelmercier]

The Yanmar workshop manual recommends full revs, 3600 rpm, for five minutes after every two hours at cruising revs...

Interesting, I wonder if Volvo Penta have the same advice?

 

[vyv_cox]

Interesting, I wonder if Volvo Penta have the same advice?

I am guessing that Yanmar are concerned more with the exhaust valves and ports than they are with the manifold. Running at full bore helps to remove incomplete combustion products i.e carbon but it most definitely also contributes to a clean manifold. Volvo's problem is that they like to issue one piece of advice for all engines, so anything from 10 HP to hundreds, maybe thousands? Their oil recommendation is a glaring example but no doubt there are many more.