MD2B cooling: any experts?

[Katouf]

Having drained the engine of salt water when I removed, cleaned and replaced the (working) thermostat, the engine temperature gauge now refuses to move from the cold area. Investigation showed that the thermostat housing was bone dry - no water was getting past the closed thermostat into the engine - hence the non reading on the gauge.
The engine runs and gets hot, too hot to touch, and water is still circulating through the small thermostat bypass-holes into the exhaust pipe. The raw water pump works fine.
The question is: if the thermostat stays closed, how does water get into the engine - or do you have to pre fill by hand in some way? If so, how? What will happen if I run the engine without the thermostat fitted? Mr Manley in his book says this is a no no!
Thanks in anticipation
Alan

 

[VicS]

I know the cooling system of the similar MD11c only too well.
The cooling water enters the engine via small passges in the exhaust manifold. The connection to that is about half way along the underside. Not obvious and we missed it at first.

These little passages get blocked. One is longer (to the rear head IIRC) than the other and is a bit more difficult to unblock than the other but a stout bit of wire will do the trick once you have the manifold off.

That may not be the end of the matter because the cooling passages in the blocks get clogged up as well and so do the smallish passages beteen the heads and blocks.
The manifold job is quite straight forward but you will need new gaskets for reassembly. Beyond that removing the heads etc gets more complicated but once you get some flow through the use of an acid boiler descaler may help.

Tackle the manifold first and take it from there.

 

[jkim1]

Thank you Vic I have always wondered how the water got in, just goes to show how good this forum can be.

 

[Katouf]

Hi Vic
Can we assume that your MDIIC is similar to the older MD2B?
Unless there is a branch off the inlet pipe coming from the pump where you describe under the manifold (I might have missed it) the only entry point to the block appears to be fed from the limited flow of the bypass where it enters the exhaust manifold. The manual seems to show the water entering the block from a hole just below the thermostat. My thermostat housing has the hole but there is no corresponding hole in the block - it's solid metal, not hardened crud.
Still mystified but will have another look this weekend - weather allowing as I'm on a swinging mooring.
Alan

 

[Kurrawong_Kid]

Has the little o-ring that should surround the "blocked up" hole in the thermostat housing dropped off? ( mentioned as crud in earlier post). When you took housing off to check thermostat it may have disappeared. If so water may not circulate correctly. This is additional to gasket surrounding thermostat. I agree with info. in all the other posts. Good Luck! You need it with an MD2B!

 

[VicS]

Yes I know about the hole in the thermostat cover. We spent some time trying to unblock a non existant hole in the front of the manifold to connect with it as well! Someone on here did explain why it is there and what it lines up with on some models. I forget the details now as it was not relevant to our needs. ( Indirectly cooled engines I think)

Look very closely at the pipe that runs under the manifold. It appears to be a continuous run from the pump to the thermostat cover but about half way along there is an inverted Tee piece that connects into the manifold.

If yours really is not like that you have me stumped. The water must branch off from the pump discharge somewhere before it gets to the thermostat cover, which is where hot water will be leaving the engine, so I'm pretty confident that you will find it more or less the same.

By the way make careful note of any electrical connections you disconnect. I reconnected something wrongly once and burnt out a section of wiring!

When you do get things sorted check the temperatures of the individual cylinder heads and blocks. Use a contact thermometer if you have access to one but otherwise by feel. It is quite possible to have water circulating through one half of the engine and not the other and this won't be obvious from the temperature guage. Also a fluctuating temperature reading, slowly rising and falling, is an indication of poor circulation around one or both of the cylinder blocks.

 

[VicS]

If the O ring is missing water will leak out and that will be obvious!

 

[Katouf]

Thanks for the good luck wishes and interest shown but no - the O ring is still there.
I think Vic has the answer in his post

Alan

 

[Katouf]

Vic
I think I can now officially label you the resident expert on an MD2B! /forums/images/graemlins/cool.gif
Thanks for all the detail. I'll let you know the outcome.
Alan

 

[Bilgediver]

Vic has covered most points but one or two have been left out.

Yes the water enters via the inverted tee into the manifold and then through cored passages and through the exhaust joint face to the head. here it circulates the head and returns to the manifold where it travels to the thermostatat.

The block is actually cooled by thermionic syphon from water up in the head and this is done via 3 cored passages around the bore and a small drilled passage adjacent to the exhaust joint. this hole is in a recess an often missed. If left blocked ou get the pulsing temperature effect and steamy exhaust.

The connection between this drilled hole and the cored passages is an annular space at the bottom of the block acting like an inverted weir and this can block with sediment. I recomend opening the drain cocks from time to time when the engine is running to clear this crud, do this when the engine is cold to avvoid thermal shock.

The thermostat housing has a lower inlet via a nozzle which can get blocked by impeller pieces and this flow is the constant exhaust cooling flow. the hot water from the head passes through the thermostat. Some thermostats can be fitted back to front and this way round dont work. The sensing bulb is towards the engine. Below the thermostat house is a smaller opening and this is opposite what looks like a small hole. This hole should only exist in engines fitted with heat exchangers and allows a faster flow rate for the hot fresh water. It should not be drilled out in sea water cooled engines.

The best place to feel the head temperatures is the core plugs however they will never be the same However neither should be comfortable to the touch when the engine is under load.

 

[chrisross]

I did not cure my md2b cooling problems until I removed the barrels and cleared out all the crud even then I was not too impressed with the cooling system performance. Sufficient flow of cooling water is important so make sure that you replace the cam as well as the impellor in the seawater pump.
My thermostat had a small bleed hole that allowed a trickle of water through even when the t/s was shut.

 

[VicS]

Yes I agree with all of that. Been there, done most of it, and got the Tee shirt.

We think we put the head gaskets on wrongly once, blocking off the flow between the heads and the blocks, as well.

In Kaouf's case there appears to be no water getting into the engine at all hence my suggestion that the first thing to look at are the passages in the manifold. It may eventually need (a lot) more work if the cylinder block passages are badly blocked. In our case the heads were Ok but they were relatively new and that is another story.
We managed to unblock the blocks sufficiently to keep things going Ok but it meant taking them off. (I'll talk about that if and when the need arises) I believe the ultimate solution is to have the liners pressed out etc. As I mentioned earlier some people are fans of cleaning with acid bolier descalers or even hydrochoric acid (obtained as brick cleaner). I would consider the descalers as they do not contain acids which are as strong as HCl but I would be worried about doing irreparable damage with an uninhibited strong acid. (By strong I am not referring to concentration. Strong, in this context, has a special meaning in chemistry)

Another thing which has been mentioned on here, although I have no 1st hand experience of it, is that the proximity of the brass cylinder drain cocks to the liners can result in them corroding through leading to water getting into the sump! I would hate to use an acid for cleaning only to discover than it was the final straw for the liners.

All of this and its not even my own engine I'm talking about. Fortunately that has meant that it hasn't been my hand in my pocket to pay for things.

 

[roger]

You could try wedging the thermostat open with something.IIf water gets though then at least you wont overheat the engine too drastically. One problem in diagnosis is that the engine block is massive and takes a long time to heat up sufficiently to be detectable.
PS We had a new thermostat fail to open on an MDII. It could be that yours is faulty.

 

[VicS]

You might just as well take it out and give it a try. Know it is always said don't run with it removed but I dont understand why not at least for a short spell.