Bukh DV 10 Overheating

bumblefish

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My E30 only returned to the water in October and on my trip back to the mooring the engine overheating alarm came on. I finally had a good look recently and found that the pipe between the impellor and the engine block had a lot of air in it, almost like cavitation. Could this be the cause of the overheating and how do I resolve it? Another possibility is that the thermostat is not opening correctly, this is a brand new thermostat and housing, not cheap! Do I need to check the opening temperature?
 

RivalRedwing

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If it is the same as the DV24.... have you removed the pipe you are referring to? The flywheel restricts access to the allen key screws but removal is possible... in it you can find bits of impeller and solid deposits which restrict flow, needs some prodding around with some wire to check the bends and clear.
 

Poignard

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You can check the thermostat by putting it in a saucepan of water and heating it up.
You should see it open when the water gets hot enough.
I think it's designed to operate at 60 degrees C. It is stamped on it.
 
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LittleSister

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I can't imagine why cavitation would occur, nor that it would result in an amount of air that would make a difference to the cooling and be obvious in the pipe you mention, so I think that's a red herring.

I'm with Poignard in suggesting first check there is an adequate supply of water to the pump (i.e. water filter clear; seacock fully open; no obstruction to hull intake, no cracked or loose intake pipe to pump allowing air in); and check impellor for damage or excessive wear.

I imagine you have changed the thermostat and housing to address a prior overheating problem, and if so I suspect that change has not solved that original problem which has its source elsewhere.
 

bumblefish

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The first things I would look at would be the water inlet strainer and the water pump impeller.

Why had you renewed the thermostat, by the way?
The spade terminals for the sensor on the housing were broken and beyond repair, the thermostat housing came with a new thermostat, it should do at £800! No other reason. I took the top of the raw water filter and opened the seacock, there was good flow. The impellor gasket was changed during a recent service so I imagine it is possible that the problem lies there?
 

LittleSister

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The impellor gasket was changed during a recent service so I imagine it is possible that the problem lies there?

Could do. (But not necessarily!)

For air to be in the pipe downstream of the pump, I think either there is a restriction in the water supply (after you've got air in the pipe for dismantling the thermostat housing) or there is an air leak at or before the pump letting air in when the pump is 'sucking'. The incoming water from the pump should displace any air in the system downstream. I doubt you'd get an air lock.
 

RivalRedwing

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one part of the OP's evidence that I was struggling with "found that the pipe between the impellor and the engine block had a lot of air in it, almost like cavitation" how did you observe this & how did you reach this conclusion?
 

bumblefish

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one part of the OP's evidence that I was struggling with "found that the pipe between the impellor and the engine block had a lot of air in it, almost like cavitation" how did you observe this & how did you reach this conclusion?
The pipe from the impellor to the engine was replaced with a clear pipe whilst she was ashore, you can quite clearly see air in the tube when the engine is running.
 

LittleSister

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You could try taking the intake pipe off the raw water filter and draw water instead from a bucket. That could check and perhaps eliminate the hull intake, seacock and filter.

You mention raw water intake. Is the engine direct (seawater) cooled, or indirect (fresh water) cooled (with a heat exchanger)? I once had a DV10 that had been converted to fresh water cooling `(with external heat exchanger) , and if I remember correctly that had a different, or modified, thermostat housing or thermostat pipe connections to standard.
 

bumblefish

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You could try taking the intake pipe off the raw water filter and draw water instead from a bucket. That could check and perhaps eliminate the hull intake, seacock and filter.

You mention raw water intake. Is the engine direct (seawater) cooled, or indirect (fresh water) cooled (with a heat exchanger)? I once had a DV10 that had been converted to fresh water cooling `(with external heat exchanger) , and if I remember correctly that had a different, or modified, thermostat housing or thermostat pipe connections to standard.
Still direct cooled. She takes a long time to get hot enough to set off the alarm, I would need a very big bucket!!!! I doubt that the impellor would draw water from a pipe over the side.
 

LittleSister

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She takes a long time to get hot enough to set off the alarm, I would need a very big bucket!!!! I doubt that the impellor would draw water from a pipe over the side.

You are not using a bucket to set off the alarm, but to see if there is a good flow of water coming out of the pump.
 
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