Volvo MD11C

[elder]

The Engine : Volvo MK11C, sea water cooled.

Problem: The cooling water circulation.
The engine starts easily enough. The boat is out the water and is cooled with mains hose.

Symptoms: The water circulates for a few minutes and then stops, after a few minutes it starts up again. Sometimes it does not.

Current situation: Whilst the boat is out the water, there is a filter box which is placed just below the waterline and about a foot above the pump.
It is fed by a mains hose at the moment but not at a high pressure or flow. This leads by hose to the water cooled gear box and to the Jabsco pump.
The gear box has been flushed out and water has flowed through without restriction.
NOTE 1
The pump was fitted with a new shaft, seals and impellor. The drive has been shown to be rotating in the correct order.

NOTE 2
A mains hose was fitted to the pipe leading from the pump outlet and the water circulated to the exhaust manifold and out to the exhaust pipe without a problem.

NOTE 3
The impellor in the pump was of course running dry and was lubricated with washing up liquid from time to time. This would indicate that the problem is the pump, but the pump rotates as it should and when disconnected from the outlet pipe, will pump out at a considerable force.

One clue which was established was when the pipes were all in place and the water circulating and then stopping, it would start to circulate again when the screws on the pump plate were loosened; very, very slightly. This would again indicate that the problem was the pump.

NOTE 4
The new shaft was made in a local engineering shop, made slightly too long and filed down to correct length.

NOTE 5
When disconnected at the outlet pipe it flows out with some force.

NOTE 6
This would indicate that there was no restriction in the pipes leading to the exhaust manifold and the exhaust pipe, which had been taken off and cleared out.

Summary: Is there an air lock?
Is there back pressure?
Is there mechanical fault?
Is the pump so efficient that it builds up a pressure in the exhaust manifold and thermostat housing?

Having the problem put down in writing may produce the logical answer. Is there something so basic I’ve missed it? I look forward to hearing from anyone with a view on the matter.




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[Paulka]

It sounds as the turbine seizes up, possibly blocked by the cover.
It happens that the "rubber" part of the turbine looses itself from the metallic center ring. Check this.

Another effect could be that the water accumulate into the silencer, and is first expelled when a certain level of water is reached within the silencer.
The sequence would repeat itself within a few seconds, depending on the volume of the silencer.
This is normal, and noticeable mostly at tick over.

Good luck.

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[jax]

Just a thought - Had this problem on the same engine a while back. Found the seal to the water filter had failed - therefore no suction. Good luck

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[kgi]

i have had this problem manifest itself a couple of times, and like Jax i have had a seal fail in the raw water strainer, i have also had the strainer crack (plastic),lastly check the water cooled elbow, i have also had this block on me..........keith

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[dickh]

Have you got a 'bad' impellor? Sometimes the bonding between the Rubber vanes and the metal central insert fails and although it looks OK, the impellor bit doesn't rotate when under pressure - this seems to tie in with your observation that it works when the screws are loosened. Make sure you have the correct impellor or try a new impellor. Check by putting a hose from the impellor input into a bucket of water, kept topped up with the hose pipe, and you will see if the impellor is pumping OK.

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I'd rather be sailing... /forums/images/icons/smile.gif

 

[drawp]

Check that the cover of the water pump is still flat using a straight edge. When I had intermittent failure with my water pump, I found that the cover had become concave and was causing cavitation within the pump.

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[scottie]

start from scratch
fit a new impeller

disconnect the pump and put hoses into a bucket see if turning the engine over by hand with the stop lever at stop and de compressor on pumps water

if so then try with starter
then replace the original pipes bit by bit checking as you go

there are three posibilties

1 you can not pump water in
2 you cant get water through and out
3 you are pumping air

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