Priming cooling water intake to avoid airlocks...

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bobholiday
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Priming cooling water intake to avoid airlocks...

Post by bobholiday »

Priming cooling water intake to avoid airlocks...

When running on land, or when returning to the water after beeing on land?

On land, I've been holding an extension to the water inlet pipe aloft, while pouring in water from a jug, until it reaches the top of the pipe and doesn't go down any more, then putting my thumb over the end of the pipe and immersing it in a large bucket in the cabin... but if I hold the pipe too high while filling from the jug, it seems to never stop going in... I'm guessing it's actually possible to overfill this way with too great a head, and potentially get water right through the system and out the other side. Is there any way this might then go back into the engine? I'm unsure what kind of valve there is to stop this happening - I assume there's something?

My engine is a Volvo MD11C.

Also - when I first put my boat back in the water after a time on land, how do you prime the cooling system so that there's no air in it? Surely it's going to be hard to avoid a bubble in the intake pipe? Or is it just not a problem?

Thanks in advance for any advice.
8)

richard
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Location: exeter

Post by richard »

Hi Bob , Richard again ........ is the cooling system on your md direct sea water cooling or fresh water around the cooling jacket and then salt water via a heat exchanger. If its the latter you have no problem as the engine wont overheat in the time it takes for the impellor to pump sea water through the system then out through the exaust

bobholiday
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Post by bobholiday »

Hi. It's raw cooled so no heat exchanger.

cpedw
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Location: Edinburgh

Post by cpedw »

Bob,
I don't know the MD11C but all the boat engines I have encountered (1 cylinder Bukh, 2 cylinder Yanmar and 3 cylinder Volvo) have been self-priming with no problem. I think it can be a problem if the pump impeller is worn.
But beware of putting water into the raw cooling system when the engine's not running. All the engines I have known had nothing except the flow of exhaust gas and possibly gravity to keep the cooling water from going back into the cylinders. This can cause a lot of expensive damage. So much so that if you're having trouble starting an engine, it's recommended to close the inlet seacock. This always seems contradictory as others will tell you that no water flowing throught he pump will cause damage to the pump but I suppose it's always a question of how long you do it for - and don't forget to put the water back on as soon as the engine fires.

Derek

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