Raw Seawater Cooled Volvo Penta MD11C Questions Re Thermostat

[CaptainBob]

Ran my engine today for the first time since I bought my boat. First time on my own. Quite exciting!!

Not sure if it's alright though.

I used a little jug to "prime" the cooling system with fresh water until it stopped going down the pipe (temporary longer pipe added for this purpose in place of seacock attachment), then put that pipe in a large bucket of water to act as "the sea".

Started the engine.

At first I got exhaust gases AND water out the back, but then it was just exhaust and a teeny amount of water.

I assumed I had an air lock, so re-primed the pipe... got some water through again for a bit.

I fiddled around a while like this, keeping a really close eye on the temperature guage.

Temperature guage got up to near 80C and I was about to give up and kill the engine quick sharp when I think the thermostat must have kicked in, the temperature dropped fairly rapidly, and a good flow of water started coming out with the exhaust.

After a bit the thermostat must have closed as the flow slowed again to a few drops and the level in my bucket stopped dropping... only to start flowing again when the thermostat (I assume) opened.

Guessing I've got a problem here? Can't be good to have my impeller trying to push water through, and have it not go through? Furred pipe in the system after where the thermostat is?

Or is this actually correct operation?

----

Additional... After I shut down the engine, I felt the cyl heads to see how hot they were to the touch. They seemed fine. Not too hot to hold my hand on for a short time.... but I was surprised to feel that the aft one was noticably hotter than the foward one... is THIS normal?

Many thanks for any insights!!

 

[PembrokeshirePromise]

From my understanding having one of these engines - the flow shoudl continue and not be determined by the thermostat (basically this just closes of the bypass and allows the water to pass through the cooling channels on the heads when the engine is upto temp)

One of the problmes with thsi engine is those chanels are quite narrow and prone to blocking - and isn't forced through these channels.

The fact that you are feeling different temp on the 2 cylinders suggests that at least one head has some blocked cooling channels I'd suggest.

I'd also suspect that there might be some other blockages if you are not seeing cooling water coming out until the thermostat opens.

Short of opening the engine up and cleaning the channels - you can try recycling cleaning fluid around the engine (search teh forum for Fernox (basically boiler descaler) - some worry about it eating seals - but I did it a couple of times and it certainly inmporved things - of course it needs some flow to be able to disolve the crud

Good luck !

 

[alisdair4]

FWIW, I had a real drama with an overheating MD11c (also 3rd time out on new boat!) . Basically, a temporary blockage of the inlet valve led to the exhauast waterlock burning out, smoke-filled cabin and a really exciting afternoon!

So the information about Fernex is really useful. On the advice of other forum users, I ran the engine through with fresh water (for about 90 minutes) to make sure there was no blockage; then antifreezed it for the winter. I will definitely replace the thermostat and impeller at the beginning of the season to eliminate any other possible causes of overheating. Presumably, I should do the flush with Fernex before changing any components?

 

[Bilgediver]

At first I got exhaust gases AND water out the back, but then it was just exhaust and a teeny amount of water.
..........................................................................................

This is not a fair test however there should be a continuous flow even with the thermostat shut.

The thermostat housing should have a bypass pipe entering in at the bottom to a fixed size nozzle however this can get blocked by bits of pump impeller. This hole is only about 3 mm in dia so the flow rate isn t that much when bye passing the thermostat.


You comment on the cylinder head temperatures..

you are probably feeling the back of one head and the front of the other head....one plug is nearer the exhaust than the other so differences can be expected. However the circulating system on the old Volvo's is so crude it would be a coincidence if both heads were ever the same temperature.

 

[FAITIRA]

If the previous owner had no probs, (ask him) I would witerise and leave alone, I had one in my Rival for years, it was bullet proof. Only time I had a prob, was being kind to it ashore and drowned it. The old addage sometimes really applies, "If it isn,t f#cked, don,t fix it".

 

[VicS]

I can confirm that you should get the full cooling water flow out with the exhaust all the time irrespective of the thermostat opening. The by pass is a smallish hole in the thermostat cover that links the hose coming in from the bottom with the flow leaving the engine via the thermostat and leaving via the hose on the top. Check that hole is clear!

( Don't be fooled by the apparent lack of a connection with the front face of the exhaust manifold below the thermostat where it looks as though there should be one .... there isn't .... you'll realise what I mean once you have the cover off )

The first problem that develops on these engines is that two small passages in the exhaust manifold that carry incoming water from the connection half way along its underside (I bet you haven't noticed that connection yet!) to the two cylinder heads get blocked (especially the longer rear one). It is fairly simple to poke them clear with a stiff wire once you have the manifold off though. Well worth doing and definitely the first thing to look at if there is any sign of overheating.

The next problem is that the water jackets in the cylinders get filled with crud. Much more difficult to do anything about without a major strip down and removal of the liners. Periodic flushing with an acid boiler scaler such as Fernox DS 3 may help to prevent too much of a build up though. (But it must be an acid descaler, a central heating system flushing solution won't do any good)

Don't place too much faith in the temperature gauge. It reads the temperature of the combined water flow from the two cylinders and is controlled by the thermostat. It is quite possible to have one cylinder over heating while the other is over cooled. You need to compare the temperatures of the two separately, with a contact thermometer or by touch.

80 C is a bit hot. the thermostat for raw water cooling should start to open at 60 C and be fully open at 75 C

When you drain the system down remember that the two cylinders have separate drain cocks. They will probably be blocked especially the elbow on which the front one is mounted and hidden behind the alternator.

If you don't have an owners manual it is available on line. I'll find the url if you need it. The workshop manual used to be but is not now. One of the forumites has one on his website though. perhaps someone knows the URL.

Well worth renewing the water pump impeller if has not been done recently and also inspecting the pump for wear.

Sorry rather brief but yell if you need any more info. I know this engine's cooling system only too well.

 

[ruvane]

I have copies of operator's and workshop manuals, so if you want a copy, send me a PM.

 

[CaptainBob]

Cheers for all this!! Plenty to work with here. I'll head back to the boat at my earliest opportunity and have a play.

I've got the following publications in hard copy:

MD11C "Do It Yourself" Manual
MD11C Workshop Manual

And I think I have the owners manual in a PDF I downloaded.

I'll come back when I have more info.

Thanks again!!!!!

 

[lucarossini]

I can confirm that you should get the full cooling water flow out with the exhaust all the time irrespective of the thermostat opening. The by pass is a smallish hole in the thermostat cover that links the hose coming in from the bottom with the flow leaving the engine via the thermostat and leaving via the hose on the top. Check that hole is clear!

( Don't be fooled by the apparent lack of a connection with the front face of the exhaust manifold below the thermostat where it looks as though there should be one .... there isn't .... you'll realise what I mean once you have the cover off )

The first problem that develops on these engines is that two small passages in the exhaust manifold that carry incoming water from the connection half way along its underside (I bet you haven't noticed that connection yet!) to the two cylinder heads get blocked (especially the longer rear one). It is fairly simple to poke them clear with a stiff wire once you have the manifold off though. Well worth doing and definitely the first thing to look at if there is any sign of overheating.

The next problem is that the water jackets in the cylinders get filled with crud. Much more difficult to do anything about without a major strip down and removal of the liners. Periodic flushing with an acid boiler scaler such as Fernox DS 3 may help to prevent too much of a build up though. (But it must be an acid descaler, a central heating system flushing solution won't do any good)

Don't place too much faith in the temperature gauge. It reads the temperature of the combined water flow from the two cylinders and is controlled by the thermostat. It is quite possible to have one cylinder over heating while the other is over cooled. You need to compare the temperatures of the two separately, with a contact thermometer or by touch.

80 C is a bit hot. the thermostat for raw water cooling should start to open at 60 C and be fully open at 75 C

When you drain the system down remember that the two cylinders have separate drain cocks. They will probably be blocked especially the elbow on which the front one is mounted and hidden behind the alternator.

If you don't have an owners manual it is available on line. I'll find the url if you need it. The workshop manual used to be but is not now. One of the forumites has one on his website though. perhaps someone knows the URL.

Well worth renewing the water pump impeller if has not been done recently and also inspecting the pump for wear.

Sorry rather brief but yell if you need any more info. I know this engine's cooling system only too well.

Hello !!

I am in the same situation. if we remove the thermostat altogether, is it important to have the little hole open?

 

[Bilgediver]

If you examine the thermostat housing you will see that the cooling pipe from the pump comes into the bottom of the housing. There is a restrictor orifice in that fitting where the pipe is connected and it can easily block with bits of rubber from the pump. This orifice is a bypass to be thermostat to ensure water flows at all times to cool the exhaust so suspect yours needs cleaning . Do not drill it any larger or you may restrict the amount of water available to cool the engine. It is a small hole about 3 or 4 mm.

I also drill a small hole in the thermostat if there is not already one there. About 1 mm is enough and this ensures the water behind the thermostats is not trapped by air.

 

[VicS]

Hello !!

I am in the same situation. if we remove the thermostat altogether, is it important to have the little hole open?

If there is no other restriction it wont matter, in fact the thermostats in some engines have a secondary "valve" which closes the bypass when the thermostat opens. ( thermostat in the MD11C may do this as well I forget)
BUT
you should not remove the thermostat , other than as an emergency "get you home" measure.

 

[lucarossini]

If you examine the thermostat housing you will see that the cooling pipe from the pump comes into the bottom of the housing. There is a restrictor orifice in that fitting where the pipe is connected and it can easily block with bits of rubber from the pump. This orifice is a bypass to be thermostat to ensure water flows at all times to cool the exhaust so suspect yours needs cleaning . Do not drill it any larger or you may restrict the amount of water available to cool the engine. It is a small hole about 3 or 4 mm.

I also drill a small hole in the thermostat if there is not already one there. About 1 mm is enough and this ensures the water behind the thermostats is not trapped by air.

Thanks a lot !!!

 

[Timisco]

I know this engine's cooling system only too well.

Hi guys,
I'm new in the forum, I'm the owner of a Pretorien 35 with a MD11d.
I'm trying to reassemble it after raw water cooling problems.
I have to figure out if my cylinder heads are ok, I have 2 pairs of them but they have the same problem, there is a hole on the wall between the inlet and the outlet of the coolant (raw water).
I attach a photo. It is supposed to be?
I hope VicS can help me...
Thanks a lot