MD2B Cooling Problems

[Pitterpatter]

Hi,

I have just put my boat back in the water and the winter seems to have brought on a new problem - that I cannot see in any other posts.

When the engine - the dear old MD2B, fired up first time, no cooling water was coming out. I stopped it quickly and tried again. Again nothing. Checked the impeller and all seemed fine so started up again and water started pumping straight away.

Next time on the boat, I tried again and again no water was coming out. I switched off and tried a few minutes later and again nothing for about 30-40 seconds then water started coming out.

I put this down to the thermostat actually doing what is says it will and directing the water around until the engine is warm then pumping it out once up to temperature (I know - the fact that it acted differently is worrying).

So last week I went for the first sail. Armed with my new knowledge I motored out of the harbour. But with the engine working it quickly built up temperature, then no water appeared and it quicky headed towards overheating. We got the sails up and switched off and forgot about it for a few hours.

As we returned to the harbour we reduced sail and sailed into the marina (always makes you popular) as we knew the engine was going to everheat. Starting up at the last minute, water immediately started pumping out, so no danger.

Has anyone seen this sort of thing before. It sounds like a thermostat issue to me, but I have been wrong many many times before so thought I would check if anyone else has seen this before I start tampering.

Thanks

 

[daveheaddon]

Hi there.....is there a new thermostat?

I had something similar to this on my old MD1B a few years back and it went away when I:

1) Removed the thermostat entirely
2) Replaced the engine with a home-built Perkins/Volvo 2010 (!)

....the latter being to save my teeth fillings as the single cylinder MD is a bit of a thumper.

Has the engine been rebuilt in any way over the Winter? It is, perhaps, drawing air into the cooling circuit?

S_W /forums/images/graemlins/ooo.gif

 

[pyrojames]

Regardless of whether the thermostat is open or closed, water should still pump out the exhaust. The t'stat simply directs water round the cooling jacket, or direct to the exhaust injection elbow, the water pumping in has to come out somewhere, and it's either the exhaust, or direct into the bilge.

It sounds most likely that your impellor is not pumping properly, or you have an air leak in the line between seacock and impellor. A leak in the pipe would normally result in a water leak when the engine is not running, assuming that the engine and pipework is below the water line. (I expect that having an MD2B you have a MAB rather than an AWB, no disrespect, I have an MAB myself)

The final check is to look at the t'stat housing. The MD2B has a small, approx 3mm diameter, hole in the bottom of the housing that allows some by pass water past the thermostat. This can occaisionlly get fouled or blocked and slow the water flow through the engine. Typically the water flow will be severly restricted and the t'stat will not open until the engine is very (~100 C) hot. When the t'stat does open there will be lots of hissing and spluttering from the exhaust and the engine temp will drop rapidly. The t'stat will then close again in the cold flow, and the cycle will repeat.

 

[Kyle2]

I had a problem with intermittent overheating of my MD1B engine. It took me a long time to find out the cause. When starting the engine there was usually no water passing through. I would then stop the engine and start it again, when the water would start coming through. Over time, the problem got worse and it could take some time before the water came through. Sometimes the water would stop in the middle of a passage, causing the engine to overheat. I eventually traced the problem to wear on the cover plate on the seawater pump. If you take the cover off, as if you wanted to look at the impeller, the inside face of the cover should be flat. Mine had an indentation worn in it the same shape as the inside of the pump. This must have been allowing air to pass round the impeller.
If that is not your problem, then you may perhaps have a leak elsewhere in the system. I agree that the thermostat should not be causing this - water would pass through the system even if the thermostat was faulty.
I hope this helps.

 

[Bilgediver]

Has anyone seen this sort of thing before. It sounds like a thermostat issue to me, but I have been wrong many many times before so thought I would check if anyone else has seen this before I start tampering.

***************************************************

We have all seen this before /forums/images/graemlins/laugh.gif You have a lazy pump....or maybe you have an anti syphon loop in the wrong place however do not blame the thermostat as Volvo thought of this one before you and the engine is fitted with a bypass supply to the exhaust which carries on even when the thermostat is closed.

HAve a good look at the pump...or get a skinny agile friend to do it for you if you have my problems. Either the pump is drawing air or the impeller is past its best before date as the symptoms you describe are consistant with the pump losing suction and not picking up. maybe the end plate is worn or grooved or the impeller worn or both . have you used more than one gasket? Did you fit a vetus high level suction strainer in the winter? Lots to look at but forget the thermostat.

 

[maxi]

No arguments with the other answers, but just one more idea for you. The Volvo hose between the skinfitting and the water pump on my MD2B suffered internal de-lamination.

Therefore we often had cooling water circulation at low revs, but as soon as revs were increased, the hose closed itself internally and we got engine overheat.

£1.50 worth of new hose sorted that one out.

 

[Pitterpatter]

All,

Thanks for the replies. I think it sounds like a leak in the system could be the issue. Thinking about it it is probably taking time for the cooling system to flood after the inlet is openned hence seeing the delay in water coming through.

Chances are I guess that it is drawing in air through the leak until the system floods of it's own accord then it can draw water through.

Thanks for all the imput guys. I am glad I asked now!

Paul

 

[Floating Weed]

MD2B Overheating

I had problems with my MD2B overheating. After checking all the obvious places, impeller, thermostat, blocked inlet/outlet the following solved the problem.
Remove the thermostat.
Make up a tank using a plastic storage box, you will need to fit tank connector in the bottom/side to connect a hose to it.
Remove the inlet and outlet water hoses from the engine and figure out a way of connecting the inlet to the tank connector. The outlet can just drop into the top of the box.
Mix a strong solution of caustic soda and water and put it in the box. This is now your reservoir for your cooling system. Be careful not to get in in your eyes. It will burn your skin too if careless.
Run the engine for a few minutes, you should see some circulation in the box. If you can let the engine warm up a little then turn off and leave for about half an hour. Repeat for a few times. This will remove the crud that has built up in the block.
Once you are satisfied that the block is clear carefully dispose of the caustic solution and use the same procedure to flush the engine with clean water. You can add inhibitor at this stage if you think it is needed.
I did this five years ago and have had no problems since.