Penta MD11 cooling water drain plugs

[Airscrew]

Hello All,

planning some winter maintenance.
I intend to flush the cooling circuit on my MD11c (Centaur).
I have read and courted advice widely, but dont find the answer on this forum.

The drain plugs (3 off - 2 in the block and 1 in the exhaust manifold) are two part assemblies, the (brass I think) stopper with a 't-bar' head, set into a body with a hex-nut, which screws into the block.

If I want to drain the cooling water from the block(s), is it advisable to remove the whole assembly (both parts) to permit more water to drain, and to permit some degree of 'rodding' if needed.
If I unscrew/remove the assembly (both parts), what sealant do I use when I re-fit.

Thanks in advance.

 

[VicS]

Hello All,

planning some winter maintenance.
I intend to flush the cooling circuit on my MD11c (Centaur).
I have read and courted advice widely, but dont find the answer on this forum.

The drain plugs (3 off - 2 in the block and 1 in the exhaust manifold) are two part assemblies, the (brass I think) stopper with a 't-bar' head, set into a body with a hex-nut, which screws into the block.

If I want to drain the cooling water from the block(s), is it advisable to remove the whole assembly (both parts) to permit more water to drain, and to permit some degree of 'rodding' if needed.
If I unscrew/remove the assembly (both parts), what sealant do I use when I re-fit.

Thanks in advance.

They are actually drain cocks. Turning the T bar should open them but they will almost certainly be seized and/or blocked. The T bars are easily broken off with very little force

Probably best therefore to remove the whole thing esp the ones on the cylinder blocks and poke out any blockage behind them. Front one is on an elbow IIRC ????

Use your favourite pipe jointing compound when refitting, or PTFE tape

Note the blocks are separate and both must be drained

 

[Airscrew]

Thanks Voc that is very helpful.
People like me, who haven't done this before, spend quite some time poring over websites and workshop manuals trying to visualise what fits where, and then poking a phone camera into dark spaces hoping to shed some light (sic) on the subject.
So yes, I think one of them has an elbow, and per your suggestion, I will plan to take off the whole fitting(s), and have a good old poke around.
I have taken the exhaust elbow off yesterday, but rather surprisingly it was in quite reasonable condition, so I will dig 'deeper' into the cooling circuit.

 

[VicS]

Thanks Voc that is very helpful.
People like me, who haven't done this before, spend quite some time poring over websites and workshop manuals trying to visualise what fits where, and then poking a phone camera into dark spaces hoping to shed some light (sic) on the subject.
So yes, I think one of them has an elbow, and per your suggestion, I will plan to take off the whole fitting(s), and have a good old poke around.
I have taken the exhaust elbow off yesterday, but rather surprisingly it was in quite reasonable condition, so I will dig 'deeper' into the cooling circuit.

In my experience the most troublesome parts of the cooling system are the water ways in the manifold that connect the water inlet on the underside with the cylinder heads.

IMO if your are really going to go to town on it it is worth removing the manifold and poking out these waterways. Easy to remove but you will almost certainly need a new gasket

 

[CAPTAIN FANTASTIC]

Every year I remove the temperature sensor (or the thermostat) and I pour 1/4 of a bottle of "Zero Lime" purchased from Tesco at less than £2. Leave it for 30 minutes and then flush out. I will remove all deposits. About four years ago, the engine was overheating a bit so I removed the manifold and soaked it in "zero lime" for a few hours as the waterways were totally blocked with hard lime scaling; I now maintain it clean by flushing it with zero lime every year. There are many other that remove scaling, but they can be aggressive and corrosive. The engine is over 40 years old and going strong. The drain plugs seize up unless they have been maintained.

 

[Airscrew]

VicS and CF, thanks for your replies.

I now also have the exhaust manifold off, and the drain plugs removed (some water came from both). So the manifold and the exhaust elbow are on the workbench at home. Visually, they dont look too bad, but I will manually clean and then soak in something like ZeroLime, and I also have a quantity of Rydlime.

For the block and head(s), obviously afloat on the boat, I intend to manually probe and clean the waterways in the head and behind the drain plugs.
Q. Can I pour (via funnel and tube) water into the head (water port not exhaust port), and expect it to flush out of the drain plug holes. The idea would be to flush out any flakes that I had loosened. OK?

I am trying to visualise the water flow.
The exhaust port is the square hole. Am I right in thinking the water flows from manifold to head through the small circular hole, goes around the valve sleeves, across the head, down into the block, round the cylinder bore (the drain hole(s) is at the bottom of that loop), back up to the head and across to the manifold through the oblong rectangular port. Yes??

So with drain open (and clear), water goes in the circular hole in the head, and out the drain(s).
Drains closed it should re-emerge fro the rectangular port.

For the full picture, when I have done all this, I intend to re-assemble and back flush a solution from a bucket using a spare bilge pump.

 

[CAPTAIN FANTASTIC]

VicS and CF, thanks for your replies.

I now also have the exhaust manifold off, and the drain plugs removed (some water came from both). So the manifold and the exhaust elbow are on the workbench at home. Visually, they dont look too bad, but I will manually clean and then soak in something like ZeroLime, and I also have a quantity of Rydlime.

For the block and head(s), obviously afloat on the boat, I intend to manually probe and clean the waterways in the head and behind the drain plugs.
Q. Can I pour (via funnel and tube) water into the head (water port not exhaust port), and expect it to flush out of the drain plug holes. The idea would be to flush out any flakes that I had loosened. OK?

I am trying to visualise the water flow.
The exhaust port is the square hole. Am I right in thinking the water flows from manifold to head through the small circular hole, goes around the valve sleeves, across the head, down into the block, round the cylinder bore (the drain hole(s) is at the bottom of that loop), back up to the head and across to the manifold through the oblong rectangular port. Yes??

So with drain open (and clear), water goes in the circular hole in the head, and out the drain(s).
Drains closed it should re-emerge fro the rectangular port.

For the full picture, when I have done all this, I intend to re-assemble and back flush a solution from a bucket using a spare bilge pump.

Looks like your manifold is not was not blocked up. Yes, if you pour water, it should flow out from the drains and everywhere else straight away. The problem is calcium build up which is hard and the best way to remove it is by using lime/calcium removals.