Yanmar 2 gm 20 f

[youen]

I am looking at a Gibsea 302 fitted with a Yanmar 2gm 20 fresh water cooled,I think the heat exchanger and the exhaust elbow had never been checked.Can they be difficult to dismantled ,is the heat exchanger prone to corrosion or electrolysis? If yes can I see something wrong without dismantling?Thanks

 

[MagicalArmchair]

I took my exhaust elbow of my 2GM20 raw water cooled unit last year - it can be fraught!

http://www.albinballad.co.uk/how-tos/remove-a-sheared-off-exhaust-elbow-bolt/

As for the heat exchanger, give French Marine in Brightlingsea a call, they have have the parts and their team have a wealth of knowledge they are not afraid of sharing.

 

[Spyro]

the exhaust elbow is a piece of cake but it can end up a nightmare if you have a seized or broken bolt. Sorry I can't tell you anything about the heat exchanger as mine doesn't have one. The exhaust elbow can look like new from the outside but it has to be removed to be inspected, Mine looked perfect but when I took it off but the inner tube fell out. You might find the pics if you search for yanmar exhaust elbow. there was a long running thread about it.

 

[vyv_cox]

My 3GM30F was installed in 1999, since when it has completed 2500 hours. The heat exchanger has never been opened. The exhaust manifold was never touched until 2015, when it began leaking. I bought a new one at a chandlery in Greece for less than the UK price and changed it in about an hour. The cause of failure was thermal fatigue, i.e. the consequence of high stresses generated as the engine heats and cools repeatedly. This is known as high stress, low cycle fatigue. Yanmar elbows tend not to corrode as much as Volvo ones.

Edit: I had forgotten that I have added this case history to the Fatigue page of my website. https://coxengineering.sharepoint.com/Pages/Fatigue.aspx

 

[awol]

I have just finished dismantling, inspecting and reassembling the heat exchanger on my 35 year old 2GMF. Easy-peasy, 2 hose clips, 4 nuts each end, move the secondary fuel filter and the tubes slide out. O-rings and gaskets are hideously expensive (like all Yanmar bits) but re-use is possible. Exhaust bend can be cursorily inspected by removing exhaust hose - if the inner tube has gone, replace the bend and gasket and empty the old bit out of the exhaust pipe.

 

[pagoda]

the exhaust elbow is a piece of cake but it can end up a nightmare if you have a seized or broken bolt. Sorry I can't tell you anything about the heat exchanger as mine doesn't have one. The exhaust elbow can look like new from the outside but it has to be removed to be inspected, Mine looked perfect but when I took it off but the inner tube fell out. You might find the pics if you search for yanmar exhaust elbow. there was a long running thread about it.

It's not a difficult job, though the cost of the gasket will probably shock you- as much as the elbow!. On a 3gm30, one of the (4) M8 elbow to manifold bolts sheared off. PITA. Removed manifold , drilled out the bolt and re-tapped the hole. There are aftermarket SS elbows in the US (in Massachusetts if I recall) at more sensible than UK Yanmar prices. I bought one while over there and it appears very well made (so far).

 

[ghostlymoron]

I had a Yanmar 2GM20F on my Mirage 28 and in my ignorance never inspected the exhaust bend - I thought it was just a hollow bit of pipe connecting the exhaust to the pipe. On reflection, what is the function of the inside bit? If it becomes detached, cooling water will still get in through the stub on the side and exit along the rubber hose.

 

[earlybird]

I had a Yanmar 2GM20F on my Mirage 28 and in my ignorance never inspected the exhaust bend - I thought it was just a hollow bit of pipe connecting the exhaust to the pipe. On reflection, what is the function of the inside bit? If it becomes detached, cooling water will still get in through the stub on the side and exit along the rubber hose.

I assume that the Yanmar design thinking is to avoid exposed metal surfaces at exhaust gas temperature. A good idea in that respect but at some cost.
My exhaust makes do with some thermal insulation wrapping upstream of the water injection point, but I wouldn't worry too much if it fell off,
and I can see any weld decay fairly easily.

 

[pagoda]

I assume that the Yanmar design thinking is to avoid exposed metal surfaces at exhaust gas temperature. A good idea in that respect but at some cost.
My exhaust makes do with some thermal insulation wrapping upstream of the water injection point, but I wouldn't worry too much if it fell off,
and I can see any weld decay fairly easily.

I think the inner tube part gives the water some more velocity away from the manifold- thus reducing the chance of any water going back towards the engine exhaust valves. It probably also removes some heat from the elbow in the process.

 

[ghostlymoron]

I'd have thought that the gas flow would ensure no water goes back into the manifold. If the double bend could be designed out it would be a great benefit.

 

[nemodreams]

On a 1gm10 raw water cooled - when running normally I can put my hand on any part of the engine - inc the elbow. With a temp warning gauge that goes off @ 63 C - I doubt if the water needs to go into the exhaust at all - it could just go out on its own.
I have been tempted to rig it up like that just to see what difference it makes to the elbow temp ?

 

[earlybird]

On a 1gm10 raw water cooled - when running normally I can put my hand on any part of the engine - inc the elbow. With a temp warning gauge that goes off @ 63 C - I doubt if the water needs to go into the exhaust at all - it could just go out on its own.
I have been tempted to rig it up like that just to see what difference it makes to the elbow temp ?

I wouldn't recommend diverting the water flow as you appear to suggest. The metal elbow will get extremely hot from the exhaust gases, esp. with the engine under load, so you wouldn't want to touch it. The rubber exhaust pipe and any plastic water-lock etc will be damaged.

 

[RichardS]

On a 1gm10 raw water cooled - when running normally I can put my hand on any part of the engine - inc the elbow. With a temp warning gauge that goes off @ 63 C - I doubt if the water needs to go into the exhaust at all - it could just go out on its own.
I have been tempted to rig it up like that just to see what difference it makes to the elbow temp ?

I wouldn't recommend diverting the water flow as you appear to suggest. The metal elbow will get extremely hot from the exhaust gases, esp. with the engine under load, so you wouldn't want to touch it. The rubber exhaust pipe and any plastic water-lock etc will be damaged.

But it's the water that's keeping the elbow cool enough to put your hand on it .... that's exactly what it's for.

Earlybird is almost certainly right.

You can have non-water cooled exhausts on boats but you need a different ducting system/silencer.

Richard

 

[vyv_cox]

On a 1gm10 raw water cooled - when running normally I can put my hand on any part of the engine - inc the elbow. With a temp warning gauge that goes off @ 63 C - I doubt if the water needs to go into the exhaust at all - it could just go out on its own.
I have been tempted to rig it up like that just to see what difference it makes to the elbow temp ?

I was forced to motor for no more than a couple of minutes without water when my water pump failed right in the middle of the entrance to Scheveningen harbour. The engine was OK but later inspection found the water trap appreciably melted.