MD2020 High Rise Exhaust Elbow

[theoldwizard1]

Originally Posted by Scubaseas

It would be nice to see what their "muffler" looks like and what the exhaust system looks like. As in is there a gooseneck?

I requested pictures of everything AFTER the elbow.

[theoldwizard1]

Originally Posted by Scubaseas

Looking at their video at 13:09 looks like they already have the air vent on the water pump">raw water pump to heat exchanger as I described.

Which video are you referring to ?

From what I have seen they have a system more like the one on the left than the one on the right.



The standard rubber "boot"/adapter from the heat exchanger makes a 90° and enters into a nipple on the top of the elbow (this is a "low rise elbow")

Originally Posted by Scubaseas

They state they have a water lock muffler and a previous video shows their exhaust pipe well above the waterline.

Again no video of the "muffler". What ever it is, I would replace it with a Vetus NLP



The question is not if the exhaust from the elbow is below the waterline, but if the exhaust from the engine is below the waterline (refer to my first two attachments)

Originally Posted by Scubaseas

So all the need to do is use the low rise elbow they already have and they're done. They need a hacksaw to cut the exhaust hose down about an inch or so.

CONCUR ! (But I would still buy the Vetus NLP.)

I don't think they own a hacksaw ! They do have a oscillating multitool (I gave it to them) with a blade that should work. (Anti-seize was also another gift as several other tools.)

Originally Posted by Scubaseas

They are a lovely couple with tons of enthusiasm but not a lot of practical knowledge.

Oh boy, are they green ! Not exactly "fast learners". (Note shrink tubing bare + and - electrical connections in the same tubing in previous video.)

[coopec43]

Originally Posted by jimbunyard

By the way, have you run the engine shown in your pictures? That setup would scare the bejesus out of me; on shutdown whatever water that's left in the hose is going to run down and slosh into whatever water's left in the muffler and if there isn't enough volume to cause immediate problems, I wouldn't be surprised if exhaust valve problems manifested themselves sooner than would normally be expected.

Yes I have run the engine and even if the hose from the waterlock to the Vetus gooseneck was 100% water it would only just fill the waterlock on closedown. (Of course that would never happen)

Thanks

[Uncle Bob]

Originally Posted by Scubaseas

Looking at their video at 13:09 looks like they already have the air vent on the raw water pump to heat exchanger as I described. They state they have a water lock muffler and a previous video shows their exhaust pipe well above the waterline. So all the need to do is use the low rise elbow they already have and they're done. They need a hacksaw to cut the exhaust hose down about an inch or so. They are a lovely couple with tons of enthusiasm but not a lot of practical knowledge.

I couldn't find a video of the boat in question nor one posted by the original poster, however the idea of installing a vented loop just after the raw water pump adds to the quantity of water that will drain into the muffler after shutdown, not desirable. It should be placed between the heat exchanger outlet and the exhaust injection point, with the run from the loop to the injection point kept as short as practicable.

[jimbunyard]

Originally Posted by coopec43

Yes I have run the engine and even if the hose from the waterlock to the Vetus gooseneck was 100% water it would only just fill the waterlock on closedown. (Of course that would never happen)

Thanks

The point isn't really if it fills the muffler enough to flood the engine (though this is of course a concern), but what happens every time you shut the engine down. Some water will always remain in both the muffler and the hose and the amount is not a constant.

Can't tell for sure the vertical fall the water will have, but it would be hard to conceive of a better design to allow water to slosh back into the vicinity of the exhaust manifold, where small amounts of both vapor and minute water droplets can/will be drawn back into the combustion chambers.

Many people find it hard to believe, but the flow of gases through an engine is
anything but uniform; that part of every exhaust cycle has a small vacuum component is the relevant concept here.

Ignore it at your own (or rather, your engine's) risk.

[theoldwizard1]

Video showing raw cooling water from thru-hull inlet, through the sea strainer, then the above the waterline vented loop, raw water pump to the exhaust heat exchanger. After the heat exchanger there is a waterlock, then a loop that goes well above the water line before going out.

With the vented loop and the waterlock, there is simply no need for a high rise elbow !

They added an exhaust flapper !

[Scubaseas]

A lot of MD2020s vented the raw water in the inlet side of the exchanger. The amount of water dropped is pretty small given how the heat exchanger is designed allows the height of water from exchanger to vented loop In their case probably about a cup of water. They have a large (HUGE) water lock muffler.



They should be aware that excessive cranking without running could flood the engine with salt water however. Valve overlap and all. I suspect that motor does not start first crank all the time. So they may want to close the water inlet if they are cranking it a long time or see if there is a drain on the waterlock muffler.



They also should loose the worm gear clamps on the engine to waterlock muffler and use T bolt style.



What they have is fine. The elbow they had really wasn't needed but I recall a lot of Volvos had that elbow regardless of if it was needed or not. One size fits all.

[theoldwizard1]

Originally Posted by Scubaseas

The (high rise) elbow they had really wasn't needed but I recall a lot of Volvos had that elbow regardless of if it was needed or not.

They definitely needed a new elbow. This was the second or third time excessive pressure on the raw water side of the heat exchanger forced sea water into the cooling water and out the the overflow/burp tank.

Originally Posted by Scubaseas

They also should loose the worm gear clamps on the engine to waterlock muffler and use T bolt style.

Educate me. Why are T-bolt clamps better than worm gear ? (Although I have heard some cheap worm gear clamps have some non-stainless parts and will fail.)

[Scubaseas]

They definitely needed a new elbow. This was the second or third time excessive pressure on the raw water side of the heat exchanger forced sea water into the cooling water and out the the overflow/burp tank.

He may also have overheat issues from filling as he may or not have the vent hole for the thermostat on the top. As in keep an eye on the temperature and be ready to refill the fresh water side as it gets to 80*C.

He may have issues other then the elbow. Not saying the elbow is not shot. I'm sure it is.

Been my experience that worm gears either vibrate loose or crack.

https://www.practical-sailor.com/sys...el-hose-clamps


https://tridentmarine.com/product/tr.../#.Xu0BjKZ7lLM


ABYC: 1 10 7 1 Every exhaust hose connection shall be secured with at least two clamps at each end to produce a secure, liquid and vapor tight joint



1.7.10 2 Clamps used for this purpose shall be entirely of stainless steel metaL The bands shall be a minimum of 1/2 inch (12 mm) in width"

[theoldwizard1]

Originally Posted by Scubaseas

He may also have overheat issues from filling as he may or not have the vent hole for the thermostat on the top. As in keep an eye on the temperature and be ready to refill the fresh water side as it gets to 80*C.

Which vent hole are you referring to ? The one in the heat exchanger insert ? (They got that right after previously NOT getting it right !)

Originally Posted by Scubaseas

Been my experience that worm gears either vibrate loose or crack.

[Scubaseas]

Which vent hole are you referring to ? The one in the heat exchanger insert ? (They got that right after previously NOT getting it right !)

There is a vent hole in the thermostat that has to be at the top or the block won't fill with fresh water all the way.

[SOLAR SUPPORT]

Hello everyone,

The video below shows the modified elbow which was made from stainless steel 316L material. This elbow is suitable for Volvo Penta d1-20,d1-30,d1-40 engines. Md2020 has a different sea water outlet which comes from the heat exchanger but I think it can be adopted to the newer series. Manifold - Elbow joint is the same with the new series I assume.

The major problems with the Volvo Penta iron cast elbow are:

1-Iron cast elbow gets rusted quickly and can't function properly since the sea water passages can't keep their original form in a few years time.

2-The salty cooling sea water splash back to aluminium exhaust manifold and leave salt deposits behind which leads the aluminium manifold to melt in time because of the galvanic corrosion.

The problem one has been solved by manufacturing the elbow from 316L stainless steel material. Allthough the problem two is solved after the problem one naturaly, the stainless steel elbow is made 50 mm. longer than the original one to make sure that the salty sea water don't splash back to aluminium manifold.

It is cheaper than the original VP iron cast elbow.

Video Link: https://youtu.be/y5RcbYMGILo

[Steve DAntonio]

You should not use any brass components in the exhaust or any raw water system. More on that subject here https://stevedmarineconsulting.com/k...rwater-alloys/

I would not rely on a check valve to keep water out of an engine via the exhaust, fine as a belt and suspenders, but they are not reliable enough as a primary means of excluding water for an otherwise non-compliant system.

Using a low riser to a water lift muffler is an option, however, it has to be done carefully, you must have enough drop between the elbow injection point and the muffler. Then, you should have an apex above the muffler and then a continuous downhill run to the hull exit from there. Several of those can be tall orders for sail auxiliary installations.

I suspect you could have one made from 316L for less than $1,000, at least in the US. There are several fabricators in FL, CA and WA, and elsewhere who do this. I honestly can't believe we still build engines and gens with cast iron raw water mixing elbows and risers.

More on exhaust system design here Exhaust system design - Ocean Navigator - May/June 2018

I've attached Volvo's installation poster, which shows details for heights, drops etc. for their various exhaust system designs.

(In Taiwan)

[theoldwizard1]

Originally Posted by Steve DAntonio

I would not rely on a check valve to keep water out of an engine via the exhaust, fine as a belt and suspenders, but they are not reliable enough as a primary means of excluding water for an otherwise non-compliant system.

The check valve ahead of the raw water pump is definitely a "belt and suspenders". Besides that, the boat in question, has a typical waterlock immediately after the elbow, which then goes to an exhaust loop that is actually above the height of the cockpit sole.

They are adding an external flapper for "good measure" !

[Steve DAntonio]

A check valve ahead of the raw water pump? That's atypical, what purpose does it serve? It could only prevent water from draining out of the engine when the vessel was hauled, but that's not necessary, water can't drain past the raw water pump. I don't like check valves and use them only if there is no other option, they are prone to failure, becoming seized in the open or closed position. Swing check valves also wear out if used for long periods.

You should have an anti-siphon valve between the raw water pump and the mixing elbow.

More on check valve weaknesses here https://www.proboat.com/2017/04/many...-check-valves/

And anti-siphon valves https://www.proboat.com/2017/06/antisiphon-valves/

(In Taiwan)