MD2B overheating (seacock open this time)

mogmog2

mogmog2

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MD2B again: I have read other posts on this, but many are unresolved.
Plenty of water coming out of the exhaust when berthed.
After a short while of motoring (<10mins at medium throttle), water stops, the temperature guage shoots up, then drops and no water still.
I have replaced the impeller, checked the intake is clear, checked the pump is outputting water, removed the exhaust elbow union rodded & flushed it, same to the pipe leading through the T piece to the thermostat housing.
Removed the housing, recovered a 2cm flake of crud, replaced the thermostat (behaviour same as with old one) but plenty of water in exhaust... initially.
I have read about 'the original Volvo Penta intake hose delaminating and blocking suction at higher revs. I took mine off and connected the sea end to a tap (I know it's not suction, so not a great test) and that was ok. Mine is clear with diamond shaped fibre reinforcement (like a garden hose) is this original?/can this delaminate.
It would seem that maybe when the thermostat is closed, the water circulates, but when it opens,it doesn't?
I'm currently investigating the manifold.
Also there is supposed to be a '3mm hole at the bottom of the thermostat'. I can only find a 1/4" hole in the thermostat housing, that runs through the top. Where is the 3mm hole?

Any ideas?
thanks.
 
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Check all the water passages in the exhaust manifold, especially the passages from the Tee piece you mentioned to the cylinder heads.

When the engine is cold water passes through the hoses connected to the Tee to the thermostat housing , through the bypass hole and then to the injection point in exhaust outlet elbow ( via the anti-siphon loop if one is fitted)
While the engine is cold the thermostat remains closed so no cooling water flows through the engine itself. When the engine reaches its normal operating temperature the thermostat opens. Water can then flow via passages in the manifold to the heads and cylinder blocks. Hot water flows from the heads via other passages in the manifold to the thermostat, where it joins with the flow through the bypass, and then to the exhaust elbow.

If the flow through the engine cooling circuits are blocked the engine will overheat, the thermostat will open fully and will I think close the bypass. Hence the total disappearance of all cooling water flow.

You may also find the water passages in the heads are choked up . Likewise the water jackets in the cylinder blocks !

I do not know where the 3mm hole you refer to is. Where are you reading about this ? Is it the water outlet from the manifold to the thermostat ?
 
As the manifold has the smaller paths ( diameter), the intake path after the T fitting should be clogged completely. Thats why when thermostat is closed, you have water flowing out of the exhaust ( just cold water not getting in the engine) . But when thermostat opens there is no water in the heads and cylinders to come out as the thermostat opens.

On the #12 post of this thread i have a pic with drawing of the cooling path of the manifold ( intake paths). With a hard wire you can do the job easily. To be sure it is ok, you should be able to blow at hole A and feel the air coming out from holes B and C

http://www.ybw.com/forums/showthrea...anifold/page2&highlight=md2b+clogged+manifold
 
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Akestor said:
As the manifold has the smaller paths ( diameter), the intake path after the T fitting should be clogged completely. Thats why when thermostat is closed, you have water flowing out of the exhaust ( just cold water not getting in the engine) . But when thermostat opens there is no water in the heads and cylinders to come out as the thermostat opens.

On the #12 post of this thread i have a pic with drawing of the cooling path of the manifold ( intake paths). With a hard wire you can do the job easily. To be sure it is ok, you should be able to blow at hole A and feel the air coming out from holes B and C

http://www.ybw.com/forums/showthrea...anifold/page2&highlight=md2b+clogged+manifold
Click to expand...

Akestor, thanks. I was following your post with interest
I have taken the manifold off and have it it at home. I found that the rear waterway (B in your photo?) that leads to the cylinder is blocked solid, so I'm now currently excavating this but having difficulty working out where it goes: my stiffer excavating wire won't follow the bend well and softer wire just buckles. Before I left the boat last night I also prodded the cylinder waterways a bit & a bit if stuff came out, but not much. I removed the rear cylinder drain cock and that flowed ok, but haven't managed to undo the forward one as the starter motor is in the way and it was getting dark.
 
Another piece of the puzzle:
All this happened only a few minutes after leaving our berth. As we entered the Narrows on the river Arun with a medium tide coming in against us, the exhaust water stopped and the guage shot up. I wasn't sure we could turn in the Narrows, with brutal sheet piling consequences for getting it wrong and it was heaving with traffic, so we had to carry on till we had an opportunity to turn. We were halfway back in when the smoke started, but again with nowhere to pull over till we had to carry on to a pontoon.
As expected, the waterlock muffler had melted. What was not expected is that i later found it was brimful of water and the water in the bilge was up to the prop shaft. To melt, it must have been dry, due to no water throughput. So after this, water was somehow added, even though the engine was in an overheated state and the thermostat sending water to the blocked route?
 
Also, I have Rydlyme. As the name suggests, this dissolves calcium deposits and the blurb states "other minerals". Anyone know this include the black sludge/deposits or would I be better off with a central heating sludge remover?
 
mogmog2 said:
Also, I have Rydlyme. As the name suggests, this dissolves calcium deposits and the blurb states "other minerals". Anyone know this include the black sludge/deposits or would I be better off with a central heating sludge remover?
Click to expand...

Most of the deposits will be magnesium carbonate, some calcium carbonate and a few others, usually mixed with carbon. Rydlyme treatment will pretty much remove everything and would be my recommendation for your symptoms.
 
mogmog2 said:
Also, I have Rydlyme. As the name suggests, this dissolves calcium deposits and the blurb states "other minerals". Anyone know this include the black sludge/deposits or would I be better off with a central heating sludge remover?
Click to expand...

If you have Rydlyme then that's the stuff to use but to be effective there must be a small open path way to allow it to get where necessary.

An alternative to Rydlyme that I might have suggested is Fernox DS3, a sulfamic acid based descaler used for central heating boilers etc

A citric acid based descaler might be more effective on black iron oxide deposits.
 
mogmog2 said:
Akestor, thanks. I was following your post with interest
I have taken the manifold off and have it it at home. I found that the rear waterway (B in your photo?) that leads to the cylinder is blocked solid, so I'm now currently excavating this but having difficulty working out where it goes: my stiffer excavating wire won't follow the bend well and softer wire just buckles. Before I left the boat last night I also prodded the cylinder waterways a bit & a bit if stuff came out, but not much. I removed the rear cylinder drain cock and that flowed ok, but haven't managed to undo the forward one as the starter motor is in the way and it was getting dark.
Click to expand...

You better start from the T hole (A) and dig towards the B with a 3mm wire that can bend a bit. ( as 2nd picture shows). I dag easily but had for days hydroclorich acid in the paths that soaked the crud somehow. I do not reccomend it, choose a lighter chemical. Unfortunately i dont think there is a way to pass a wire from B to C because the path is not straight ( at least i couldnt do it). BUT its unlikely that B to C is blocked. Check this fast by sealing with your thumb the A hole and blow in B hole. Do you get air in C? if yes then you will have to unblock A to B path only where you have acces with the wire!
 
Akestor said:
You better start from the T hole (A) and dig towards the B with a 3mm wire that can bend a bit. ( as 2nd picture shows). I dag easily but had for days hydroclorich acid in the paths that soaked the crud somehow. I do not reccomend it, choose a lighter chemical. Unfortunately i dont think there is a way to pass a wire from B to C because the path is not straight ( at least i couldnt do it). BUT its unlikely that B to C is blocked. Check this fast by sealing with your thumb the A hole and blow in B hole. Do you get air in C? if yes then you will have to unblock A to B path only where you have access with the wire!
Click to expand...

Thanks, I had initially tried to undo the T piece on the boat, but bottled out as it didn't want to come & I didn't want to break it. However I put it in the vice & gently twisted the manifold & it undid. Would be very hard to clear the pathway with this in place...

Just spent all morning digging. I initially dropped water in using a pipette to flush out my diggings with various bits of wire, then moved outside & put the hose on it periodically. I now have a good flow through both holes. I dug & flushed elsewhere and a small (smaller than a pea) sized piece of impeller came out of the thermostat orifice, along with a flake of crud the about 1cm sq area.

I've just ordered a load of parts (new, reinforced suction water intake hose, muffler etc , so will reassemble tomorrow hopefully. But will dig around in the engine a bit more & flush with a hose before reassembling. Then I'll run Rydlyme through.

Whilst I was at it yesterday, I checked the (new) impeller (OK) and went to flip the cover plate over. Only when I scrutinised did I realise that it wasn't flat. like a watch glass: it was concave (from the impeller's perspective, so I gently hammered it flat, checking on a straight edge then flipped it over.

In all my reading about water pumps (gotta have a hobby), I've never seen dishing of the cover plate mentioned.

I will install the new intake hose & check all joints for intake air leaks, the pump has a "new" non-worn cover plate, new impeller & was pumping nicely before all this anyway.

I know this is an impossible question, but what are the chances that this will be the cure of the problem? I think elsewhere, VicS said that blocked manifold waterways would not prevent water from going into the exhaust, so what else to look at?
Cheers
 
mogmog2 said:
I think elsewhere, VicS said that blocked manifold waterways would not prevent water from going into the exhaust, so what else to look at?
Cheers
Click to expand...

Thats right, The flow to the injection point in the exhaust outlet elbow is quite simple and straightforward. From the water pump to the inverted T, across the "top" of the T to the bottom connection on the thermostat housing, Through the by pass in the housing, out of the top connection, back across the top of the manifold to the injection point.
If the hoses are clear, the bypass hole clear and the injection point clear there is nothing else to stop it ......... except..... I think ( but I am not sure about this ) that when the thermostat is fully open , it will close off the bypass ensuring that all the water is diverted through the cylinder heads and blocks.

There should therefore always be a water flow to the exhaust outlet bend. Through the bypass alone when the engine is cold. Partly through the engine and party through the bypass at normal operating temperatures. Through the engine alone if it overheats .
 
Thanks Vyv & VicS
.
VicS, I know the bypass in the top of the housing is clear. May have some scale, but is definitely reasonably free-flowing. Presumably an inadequate amount of water returning to the exhaust just gets vaporised so nothing to see?

As soon as I can clear my desk I'll be down there... The manifold pathway is now pretty much clear, so there'll be good circulation there to facilitate Rydlyme action. What is happening in the blocks is anyone's guess, but I'm not opening the engine up...

FWIW & rang Rydlyme & asked about black sludge. First person was very uncertain & put me through to someone else but he didn't know either! "it depends whether the sludge - whether it falls in the range of iron oxides dealt with by the Rydlyme.
Having said that, if it's mainly carbon not magnetite then it's neither here nor there, but I would have thought they would have known. Your responses inspire more confidence in their product than they did!
 
At risk of stating the obvious, Rydlyme can only work if it can "get at" the calcium deposits, and if the bores are well clogged up, it cannot do so in large enough quantities to make a difference.

Oh, and in the same vein, do check the price of a head gasket before you take the heads off.

"And finally".. if you are in a "hard water area" then the seawater in estuaries in that area will be "hard" too. DAMHIKT.
 
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