MD11c bleed hole in exhaust manifold.

[dur]

Could anyone tell me how large the hole between the thermostat housing and front of the exhaust manifold should be? We overheated on the way to the Yarmouth Gaffers festival and in my ignorance I poked a screwdriver through where I thought the hole should be. This appeared to get us some water flow so we carried on at low revs and sail. I have now read several previous posts on the MD11C and cooling and wonder whether I should now repair the ugly hole I made or leave as it is.

I now have the manifold off and can see that one of the waterways needs more of my careful poking technique:

The other doesn't look too bad to my inexperienced eye:

.

I am getting water out of the drains on the side of the block so I guess they are not too bad.

The impeller is fine (apart from me shearing one of the screws on the cover - a mole grip did good service there!) and plenty of water flows into the boat when the seacock is opened.

When we got going again the temperature then fluctuated from rather cool to rather hot - up and down all the time. Coming home it sat steady in the middle how it should be /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif.

 

[Anonymous]

While you clearly have some cleaning up to do, the big problem with the MD11C is the impellor facing plate. If scored or worn either reverse it or fit a new one. I had no joy with the Speedseal on my MD11C though others have had no problems.

 

[Bilgediver]

If you mean the secondary port under the thermostat then if your boat is sea water cooled then there should be no hole....it is a mistake to poke away at it and clear it.

Did you check the bypass hole through the back of the thermostat housing. this allows water to pass direct to exhaust when the thermostat is closed and can get blocked with bits of impeller.

Is the small hole in the thermostat clear...about 1.5mm Dia

Your symptoms are indicative of silting up in the blocks so check if any sand is coming out of the drains when you let the water flow. do this before the engine warms up.

Let us know what you find

 

[VicS]

There is not normally a hole below the thermostat on a MD11C! I know I tried to find a way through but fortunately stopped. (I know there is a connection and an O ring on the t'stat cover but it does not link to a hole in the manifold)

The passages that normally become blocked are the two from the connection on the underside leading to the cyl heads (the small round hole in your pictures)

What does the hole you have made link to. If it links to the space which accommodates the thermostat then you will have to repair it. Likewise if it opens into the exhaust gas passage. But does it join up with the passages mentioned above. Maybe leave it if it does. On second thought that could lead to over cooling the front cylinder but under cooling the rear one. Repair it

 

[dur]

I hadn't thought of reversing the plate. I'll do that once I have the old screw out. I'm not sure if there room for the speedseal as the gearbox filler is close. You can see that it has been hot in the past though it wasn't on this occasion.

 

[dur]

[ QUOTE ]
If you mean the secondary port under the thermostat then if your boat is sea water cooled then there should be no hole....it is a mistake to poke away at it and clear it.


[/ QUOTE ]
Well it is the hole at the bottom - nearest the hose - in the picture above. It is true there was no obvious hole but there was a soft spot of metal which I poked with a marlinspike and it went part way through so I tapped it with a screwdriver to finish it off. Not pretty but it was that or go home at the time!
So why is the an O-ring on the stat housing at this point? It seems to go into one of the manifold waterways but I have not studied it properly yet.

Where is the bypass hole you mention? I'll check the stat hole.

 

[dur]

I was surprised that the small holes were still relatively clear. Is it ok to use wire to have a go at rodding out these holes?

Shall I use my old screwdriver technique on the blocked waterways in the first picture? I guess it wouldn't harm as long as I am careful.

I guess I can repair the hole I made with some metal filler or similar goop as long as it can stand a bit of heat.

I have seen your posts on cleaning solutions and hope to leave this till next winter.

 

[petersto]

Dur
The hole or what looks like one in the thermostat housing should definately not be open. A chap in our club made that mistake and it was bye bye engine. I almost fell into that trap myself but hit clean metal and stopped. What I did do was take the manifold off and scraped and cleaned everything, engine and manifold then reassembled and run the engine on a mixture of Furnox(spelling)(central heating cleaner) which I had from B&Q. The crap that came out was unbelievable. Engine been running for three years now and temp bang in the middle of the guage, never falters. Make sure you do a test on the thermostat after all yout troubles. Best of luck.

 

[Bilgediver]

So why is the an O-ring on the stat housing at this point? It seems to go into one of the manifold waterways but I have not studied it properly yet.
**************************************************

The O ring is there because there is water present at this point in the housing and when the engine is FW cooled with intercooler this port is drilled out. All to do with temperature flow rates and gradients.

The by pass is in the thermostat housing and is where the hose in the vee of your hand in the first picture is connected to the housing.

Go easy with the spikes and screw drivers as high pressure water should do the job.

If you are throwing water around then it may be worth removing the screw in part of the drain plugs completely and gatting a good flow through the block.

You oscillating temperature syndome is indicative of blocked ports in the blocks at the head joints however you might flush them clear. May even be worth putting water in via the drain plugs.

Make sure with all this water around you do not send any water to the exhaust bend as this will find its way to places you don t want it to go.

Did you check the wee hole in the thermostat valve. I have stabilised temperatures by enthusiastic cleaning of this hole with a 2 mm drill.

 

[Bilgediver]

It will be as quick to take the whole pump off as only two bolts......just be sure not to replace it upside down as it will be pumping the wrong way!

 

[dur]

Now it makes sense!

I will clean up and repair my hole with some plastic padding chemical metal, carefully clean any loose blockages I can see and then new stat, gaskets, impeller face plate, if I can get it, and then circulate fernox round and round - I can provide a seperate water feed to the exhaust while doing this. I'll let you know how I get on.

Thanks all!

 

[dur]

Cleaned the manifold tonight. Discovered that the tee which feeds the water into the manifold before its trip around the engine was very restricted. Could well have been the problem. Viakal descaler seemed to be very effective - lots of fizzing - followed by a good old go with the pressure washer. My newly made port was quite uesful for flushing!

The block and heads won't be so easy to clean - I'm not using a pressure washer in the boat! At least I can now get a circulation so a bit of acid or Fernox should be able to get at it.

 

[dur]

Just to let you know...

I cleaned my temporary port with an electric wire brush...

and then filled with an epoxy putty.

I then bolted the manifold back on, overtightened it and broke one of the bolts with a loud ping /forums/images/graemlins/mad.gif /forums/images/graemlins/frown.gif

Mercifully part of the thread wa still attched and it came straight out. More luck than I deserved I know.

One week later and new bolts done up very gently I rigged up a re-circ system and poured in some Holts Rad Flush...

After half an hour I had a pretty hot bucket of green water! Green?

All back together and plenty of water out the back but the engine seems to be running very cool. Could be the new stat is stuck open. A little more testing and fiddling required.

 

[grunter10]

Its been a few yrs since this was posted but this is the best info I have found on my MD11C cooling problems. In regard the pic of the manifold waterways above I assume these need to be clear ? as on mine both manifold and engine side are totally blocked. I did not want to dig around in case I created an extra passage were there shouldn't be....