Update on reduction gear cooling

[PuffTheMagicDragon]

Further to my earlier posting regarding cooling of a Volvo Penta reduction gearI have now removed the reduction part from the MS gearbox to see where the water was coming through. No sign. We rigged up two rubber hoses and filled them with water to give around a 1 metre head of pressure (twice of what thehere would be in real life when the motor is not working and the seawater intake is left open. So far there is no sign of any seepage.

The reduction end

The set-up


The oil, when drained, looked like Bailey's Cream (yuckh). VicS had suggested that it does not take much water to emulsify into a milkshake. I am now inclined to believe that the water was not salkwater from a leak but condensation that had accumulated within the gearbox through five or six years of non-use and very little, if any, during the previous four.

Am I being unrealistically optimistic?

 

[john_morris_uk]

I had an engine once that hadn't had much use for several years. It also didn't have many hours use before. Practically ALL the seals had dried up and nearly all of them failed over the first few months of use.

As Vics says, its doesn't take much water in oil to produce an emulsified mess.

 

[philip_stevens]

.....plus the fact that when the engine is running, it is "sucking" water through the reduction gearbox, so if there was a leak, in time it would have "sucked out" all the oil.

So if there is no leak, then VicS's suggestion of condensation sounds valid.

 

[david_bagshaw]

While you have got it out , try hot water, just incase......

 

[PuffTheMagicDragon]

While you have got it out , try hot water, just incase......

...the reasoning being? I don't think that hot water would be appreciably thinner to make a difference..or would it?

 

[PuffTheMagicDragon]

.....plus the fact that when the engine is running, it is "sucking" water through the reduction gearbox, so if there was a leak, in time it would have "sucked out" all the oil.

So if there is no leak, then VicS's suggestion of condensation sounds valid.

That is also my reasoning. I do hope that we're correct.

 

[PuffTheMagicDragon]

I had an engine once that hadn't had much use for several years. It also didn't have many hours use before. Practically ALL the seals had dried up and nearly all of them failed over the first few months of use.

As Vics says, its doesn't take much water in oil to produce an emulsified mess.

Seals and hoses are being replaced as we go along, as are also the hose clips. Never realised that it had so many!

 

[sarabande]

is there any knowledge of a previous (temporary) flooding event when the box might have been covered with water, and sucked in.


I am a little unconvinced about the condensation thesis as, if the water test shows no leak, then the box is airtight. If it is airtight then any humid air inside will not be refreshed, so the amount of water in say 2l of air will be very small and unlikely to make the oil go milky.

The ideal gas law (PV = nRT) will give an answer for the absolute humidity, and hence the volume of any water entrapped in the box.

 

[john_morris_uk]

is there any knowledge of a previous (temporary) flooding event when the box might have been covered with water, and sucked in.


I am a little unconvinced about the condensation thesis as, if the water test shows no leak, then the box is airtight. If it is airtight then any humid air inside will not be refreshed, so the amount of water in say 2l of air will be very small and unlikely to make the oil go milky.

The ideal gas law (PV = nRT) will give an answer for the absolute humidity, and hence the volume of any water entrapped in the box.

Tim,

Can you empty your pm mail-box a bit please?

 

[david_bagshaw]

...the reasoning being? I don't think that hot water would be appreciably thinner to make a difference..or would it?

expansion making a crack open.

 

[PuffTheMagicDragon]

expansion making a crack open.

I see what you mean, David. It is highly improbable, however, given that the linear thermal expansion coefficient of grey cast iron is only 10,5 ppm/*C. Even with an extreme theoretical temperature gradient of 80 degrees - ambient temperature of 24 degrees right up to boiling point of seawater, say, 104 degrees - we are talking about 840 ppm. This is less than one thousandth of an inch - over a length of one inch - and is unlikely to be significant in this scenario. IMHO.

 

[PuffTheMagicDragon]

is there any knowledge of a previous (temporary) flooding event when the box might have been covered with water, and sucked in.


I am a little unconvinced about the condensation thesis as, if the water test shows no leak, then the box is airtight. If it is airtight then any humid air inside will not be refreshed, so the amount of water in say 2l of air will be very small and unlikely to make the oil go milky.

The ideal gas law (PV = nRT) will give an answer for the absolute humidity, and hence the volume of any water entrapped in the box.

No flooding that I know of, Tim.

The assumption that the box is airtight does not hold water - if you'll pardon my little pun. The gearbox is linked to the reduction gear housing vis the spaces around the balls in two bearings and by a connecting passage in the lower part of the reduction housing. The oil in this bath is kept from flowing out by a sprung rubber seal with a U-section and a thin rubber lip labyrinth around the coupling. This seal has failed, leading to the loss of some oil and to any airtightness being compromised. Relative humidity is frequently 85-90%, possibly even higher on a boat.