MD11C Cooling System - exhaust

[CPD]

I need help in confirming how I think this works before ripping into it to find out why the engine is running hot, so ......

Am I right in thinking that the water injection elbow is bolted onto the engine (rear upper starboard corner) and that this is where the cooling water, either direct from the thermostat or via the cooling block) is sprayed into the exhaust gas ?. The combined exhaust gas and water then travels combined through the heavy hose before being thrown out at the rear ?

Many thanks - I like to thoroughly understand before I set-to with the spanners !.

 

[2Tizwoz]

I have a picture of one which has been carefully cross-sectioned in order to show the inner workings.

.

They can become choked with scale and carbon thereby restricting the gas flow. The overheating may be related to scaled waterways in the engine, a damaged impeller or otherwise restricted water supply.

The exhaust hose may pose the greatest dismantling challenge. /forums/images/graemlins/blush.gif Requires a certain amont of brute force and ignorance.

 

[Superflid]

[ QUOTE ]

Am I right in thinking that the water injection elbow is bolted onto the engine (rear upper starboard corner) and that this is where the cooling water, either direct from the thermostat or via the cooling block) is sprayed into the exhaust gas ?. The combined exhaust gas and water then travels combined through the heavy hose before being thrown out at the rear ?

[/ QUOTE ]

Yup, sounds about it....

 

[VicS]

Yes. The water from the engine cooling combines with the water bypassing the engine in the thermostat cover then it all flows through the hose and pipe above the exhaust manifold and finally enters the "elbow" to mix with and cool the exhaust gases.

I dont think the one in Tizwos's picture is off an MD11 as I think they are not threaded but have a two bolt flange on to the manifold (ex MD5 perhaps)

If I have not said so before after checking pump, strainer and all exterior pipework the first things to look at are the two small passages in the exhaust manifold that carry water from the inlet connection on the under side to the two cylider heads. Poke them clear with a stout wire.

 

[2Tizwoz]

The flange unscrewed and I re-used it.

I made the rotted part in stainless. My engine is an MD7B however the elbows appear to be identical.

This picture of an MD11C elbow was posted on the Small Boat Club site.

 

[jimbouy]

Yep... you are correct in how and where...

I have just taken mine off as it developed a leak.
This picture shows the old one.

Mine is a fixed flange but the guy at keyparts says some MD11c's use a threaded flange. Best to take it off and see which sort it is. If its threaded it will be obvious once you get a close look.


Cheers


Jim

 

[PeterGibbs]

Before you dismantle enything in this area check that the thermostat is working ok - take it out, simple with this engine, and boil it gently in a saucepan to see if the contacts open. Renew if dodgy - not expensive.

There is a chance that the rubber exhaust pipe, if old, is delaminating - if so, it will impede the exhaust and cause heat backup. But if the exhaust flows freely at the exhaust point, this is less likely the issue.

Finally, the galleries in the engine can get furred up so that circulating water is inhibited from removing heat. There are mixtures you can use to remove scale without dismantlilng the engine!

Unless the elbow is bust - and this happens with all these engines eventually, and this will be clear to see - it's not worth going in there - it is most unlikely that overheating is caused in this part of the engine!

PWG

 

[VicS]

[ QUOTE ]
check that the thermostat is working ok - take it out, simple with this engine, and boil it gently in a saucepan to see if the contacts open.

[/ QUOTE ] No it should open long before the water is boiling.
To be more precise about it heat it <u>slowly</u> in a saucepan of water and check that it <u>just begins to open</u> at the specified temperature of 60C, which should be stamped on it, and is fully open at 75C which may also be stamped on it.