Milky oil in my saildrive. What do I do?

Stu Davies

While changing his engine oil, Chris Mardon noticed milky oil in his saildrive. Will it have caused damage to the leg? Stu Davies has the answer

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My yacht Spook, a Dufour 40, has a Volvo sail drive.

Last November while changing the engine oil I noticed the gearbox oil had changed to a creamy opaque colour and its level had risen to nearly overflowing; a clear sign that the prop shaft seals had failed.

She’s been left idle at her berth since November so I expect the sea water and oil will have separated in the saildrive leg.

drive shaft removed, cleaned and ready for inspection

The drive shaft is removed, cleaned and ready for inspection. Credit: Chris Mardon

My question is whether you think this will have caused damaging corrosion within the leg.

The output shaft is stainless steel but is the input shaft?

I doubt the taper roller bearings are stainless.

Should I be prepared to replace them?

Chris Mardon

Stu Davies replies:

I’ve been involved in Portugal with a friend’s yacht with the same issue recently.

Basically, the sea water gets in and emulsifiers, causing milky oil. It usually stays emulsified depending on use.

It’s a common thing to happen and the basic pieces such as the internal shafts and gears are usually OK.

Parts of a Propeller and drive shaft housing removed from a boat for cleaning following the discovery of milky oil in the gearbox

Propeller and drive shaft housing components were stripped down and cleaned. Credit: Chris Mardon

The bearings usually get pitted, though, so will need replacing along with the seals – but it’s a fairly simple job.

So lift the boat, take off the propeller and undo the housing holding the lower drive shaft in and remove it all.

Clean the internal bits of the housing well – car brake cleaner is your friend here.

The job is reasonably straightforward and my friend in Portugal who has never done the job before managed it with me on call remotely from the UK!

The drive is designed for the marine environment so I wouldn’t worry unduly about the big bits – just change the bearings, the seals and the anodes if they are worn.

Continues below…

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