Exhaust elbow.. when to remove and clean?

[Nostrodamus]

I have enjoyed this thread and as usual I have learnt a little more. Thank you to all those who contributed.

The chances are I am running my engine a little low on the revs side (usually about 2200/2300 on a volvo MD22P), but is sounds right around those revs.

A good blast on occasions and varying the revs occasionally is something I should do.

A mechanic told me running the engine on lower revs is not so much a problem provided that the engine gets up to operating temperature. The problems caused can be worse if you are constantly using the engine only for short periods (ie getting in and out of marinas) and you don't let the engine get up to its operating temperature before switching it off.

An exhaust elbow is something to keep an eye on but of course it is not the only thing. We have a sail drive and I know that creatures like living around the raw water intake holes. An occasional dive to clear these can lower the engine temp a few degrees.

I should imagine that props can also make a difference to the general operating specifications of a particular engine. I don't know but obviously some props may work the engine harder than others at a specific rev range and pitch will make a difference as well. Same as growth on the prop.

I suppose the manuals give a very general picture but it is a case of knowing your own set up and noticing when things change.

I don't know if I am like other as we have engine temp and oil pressure dials in the cockpit. They become a bit of a fixation and are looked at numerous times during the time I have the engine on. At least if they were below I wouldn't have to worry so much if the temp rose by one degree over norm.

 

[Contest1]

Great info.
I,m getting a lot of steam and spurts of warm water at the exhaust outlet of my 3GM30, Sea water cooled.
Tried some brick cleaner but much the same.
My cooling water leaves the engine block via a 12mm plastic pipe, goes up to an anti syphon valve and then back down and into the exhaust manifold.
Is this the " mixing elbow" or is it something else?

 

[cmedsailor]

Great info.
I,m getting a lot of steam and spurts of warm water at the exhaust outlet of my 3GM30, Sea water cooled.
Tried some brick cleaner but much the same.
My cooling water leaves the engine block via a 12mm plastic pipe, goes up to an anti syphon valve and then back down and into the exhaust manifold.
Is this the " mixing elbow" or is it something else?

The mixing elbow is where the sea (cooling) water and gases mix and then follow the, most probably black and thick, exhaust hose.

 

[sam_uk]

I'd persevere with the brick cleaner a bit. Leave it in the engine block for 4-6 hours.

When I did mine if I listened carefully I could hear it reacting with the deposits. Took a while but worked.

 

[davidportwain]

After only 500 hours the elbow on my D1-20 was found to be completely blocked with carbon. Its been replaced at great expense, and I have kept the old one. What to others recommend for cleaning it out with?

 

[JumbleDuck]

After only 500 hours the elbow on my D1-20 was found to be completely blocked with carbon. Its been replaced at great expense, and I have kept the old one. What to others recommend for cleaning it out with?

Engine reconditioners use hot caustic soda to decarbonise. This is nasty stuff, to put it mildly, and although it's easy enough to get hold of, as drain cleaner, I'd prefer not to play around with it myself. If you have an engine reconditioner handy, it might be worth asking them if they'll do the job, particularly if you knock he big lump out first.

 

[Stork_III]

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

MD2*** series Owner's Manual says operate at 300-500 rpm less than max revs at WOT.

 

[charles_reed]

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/

Yanmar advise removal and cleaning every 1000 hours on the 3YM. Mine has done <2000 hours, without clearing.

The release valve on the non-return valve is a different matter. Mine is taken off, soaked in fresh water and then sulphamic acid solution, before being re-assembled with new O-rings, at the end of every season (about 350 hrs). I've found this to be essential to prevent drips. Of course, if you have one of those which empty overboard, it's probably unnecessary.

 

[charles_reed]

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.

Conversely, my YM manual specifically warns against using maximum revs or cruising revs, for more than very limited periods.

I quote:-

NOTICE

This engine is designed for pleasure boat applications.
This engine is designed to operated at:-

Full throttle (3600-3800 rpm) for less than 5% of total engine hours (30 minutes in every 10 hours).
Cruising speed (3400 rpm or lower) for less than 90% of total engine time. (9 hours out of 10)

On the stick on label for use by operators it does recommend "race the engine from time to time when operating at low speeds for a long period.

As my understanding of these instructions is so contrary to yours, could I suggest you refer again to the workshop manual?

It is possible, of course that the design of the GM series was so radically different from the YM series that so completely opposite instructions were published for the two ranges but my memory of the 2GM manual I had was very similar in content to that published above.

 

[jwilson]

Conversely, my YM manual specifically warns against using maximum revs or cruising revs, for more than very limited periods.

I quote:-

NOTICE

This engine is designed for pleasure boat applications.
This engine is designed to operated at:-

Full throttle (3600-3800 rpm) for less than 5% of total engine hours (30 minutes in every 10 hours).
Cruising speed (3400 rpm or lower) for less than 90% of total engine time. (9 hours out of 10)

On the stick on label for use by operators it does recommend "race the engine from time to time when operating at low speeds for a long period.

As my understanding of these instructions is so contrary to yours, could I suggest you refer again to the workshop manual?

It is possible, of course that the design of the GM series was so radically different from the YM series that so completely opposite instructions were published for the two ranges but my memory of the 2GM manual I had was very similar in content to that published above.

I read that to say that 3,000 - 3,400 rpm 90% of the time is perfectly OK: in practice few users drive their engines that hard continually. I regard 2,600 - 2,800 rpm as cruising revs, with an occasional minute at full throttle.

 

[vyv_cox]

Conversely, my YM manual specifically warns against using maximum revs or cruising revs, for more than very limited periods.

I quote:-

NOTICE

This engine is designed for pleasure boat applications.
This engine is designed to operated at:-

Full throttle (3600-3800 rpm) for less than 5% of total engine hours (30 minutes in every 10 hours).
Cruising speed (3400 rpm or lower) for less than 90% of total engine time. (9 hours out of 10)

On the stick on label for use by operators it does recommend "race the engine from time to time when operating at low speeds for a long period.

As my understanding of these instructions is so contrary to yours, could I suggest you refer again to the workshop manual?

It is possible, of course that the design of the GM series was so radically different from the YM series that so completely opposite instructions were published for the two ranges but my memory of the 2GM manual I had was very similar in content to that published above.

My manual says exactly the same, under 2.1 Product explanation. Under Operation, section 3. Paragraphs 7 and 8. it says:

'(7) When operating the engine at low speed for long periods of time race the engine once every 2 hours.

With the clutch in neutral accelerate from the low speed position to the high speed position and repeat this process about 5 times. This is done to clean out carbon from the cylinders and the fuel injection valve. Neglecting to race the engine will result in poor exhaust colour and reduce engine performance.

(8) If possible, periodically operate the engine at near maximum rpm while underway. This will generate higher exhaust temperatures, which will help clean out hard carbon deposits, maintaining engine performance and prolonging the life of the engine.'

 

[Tranona]

Conversely, my YM manual specifically warns against using maximum revs or cruising revs, for more than very limited periods.

I quote:-

NOTICE

This engine is designed for pleasure boat applications.
This engine is designed to operated at:-

Full throttle (3600-3800 rpm) for less than 5% of total engine hours (30 minutes in every 10 hours).
Cruising speed (3400 rpm or lower) for less than 90% of total engine time. (9 hours out of 10)

On the stick on label for use by operators it does recommend "race the engine from time to time when operating at low speeds for a long period.

As my understanding of these instructions is so contrary to yours, could I suggest you refer again to the workshop manual?

It is possible, of course that the design of the GM series was so radically different from the YM series that so completely opposite instructions were published for the two ranges but my memory of the 2GM manual I had was very similar in content to that published above.

Can't see any real contradiction. 5 minutes every 2 hours is not a lot different from 30 minutes every 10 hours. It states total running hours, not time in a period. In other words there is not the expectation that every 2 hours you should run 5 minutes at WOT, only that the total time should not exceed that - ie 25 minutes in 10 hours, rather than the 30 minutes in the earlier instructions.

The whole point of the advice is to avoid running for long periods at light load or low revs. Auxilliaries are not expected to run for long periods at WOT as they are usually geared for comfortable cruising at 65-70% of max revs, which on these engines is around 2300-2500 rpm.

 

[charles_reed]

My manual says exactly the same, under 2.1 Product explanation. Under Operation, section 3. Paragraphs 7 and 8. it says:

'(7) When operating the engine at low speed for long periods of time race the engine once every 2 hours.

With the clutch in neutral accelerate from the low speed position to the high speed position and repeat this process about 5 times. This is done to clean out carbon from the cylinders and the fuel injection valve. Neglecting to race the engine will result in poor exhaust colour and reduce engine performance.

(8) If possible, periodically operate the engine at near maximum rpm while underway. This will generate higher exhaust temperatures, which will help clean out hard carbon deposits, maintaining engine performance and prolonging the life of the engine.'

I have that too. Immediately after it tells you to race the engine before turning it off, then tells you to let it idle for 5'.

I have the feeling that there is more than an element of translation drag here - shall you or I write to Sugita @ Yanmar in Osaka? He's a charming chap with good English who advised me to stick to the instructions printed at the beginning of the manual.

 

[vyv_cox]

I have that too. Immediately after it tells you to race the engine before turning it off, then tells you to let it idle for 5'.

I have the feeling that there is more than an element of translation drag here - shall you or I write to Sugita @ Yanmar in Osaka? He's a charming chap with good English who advised me to stick to the instructions printed at the beginning of the manual.

Why would I write to him when I am perfectly happy with the advice? Surely nobody can doubt that the 'Italian tune-up' is effective? When I run flat out occasionally copious clouds of black smoke are emitted for the first minute or so, gradually clearing. Seems good evidence to me that carbon is being cleared out and combustion has been improved. I also suspect that it helps to clear the manifold of salt and carbon accumulations.

 

[garvellachs]

I've just renewed the head gasket on our old Yanmar 3HM. The stainless exhaust elbow was apparently fine but there was a layer of hard carbon two or three mm thick. I fitted a new elbow (because I had a spare) and took the old home to clean up. Scraping away the carbon with a blunt screwdriver seemed to take corroded metal with it. When it was fairly clean but rough-looking I experimented by blocking the water inlet and filling the water sleeve with water from other end. Worryingly, water leaked out of the outer sleeve into the exhaust, so it had corroded right through (or I had scraped right through).

So it looked OK at first but it's in the scrap bin now. The engine is from 1984 and has about 1600 hours on the meter.