Mystery water in engine oil

single

single

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At the weekend i checked the engine over before a planned 6hr motor and discovered water in the oil. The dipstick was grey but still oil viscosity like, but the filler cap was like grey yoghurt. I did a few oil/filter changes and all looked good so went off cruising checking it every hour. All is still perfect after about 8 or 9 hours running so what caused it? The fresh water side of the engine hasn't lost a drop so it must have been sea water. The exhaust has an anti-syphon valve fitted. If while cranking i had filled the exhaust, surely it would have hydraulically locked the engine? Maybe the jabsco seawater pump seals leaking? Any other suggestions? (Thornycroft T-95) Ps. On the first oil change there was about 0.5ltr of 'extra fluid' in the sump.
 
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If your seawater pump is bolted onto the crankcase rather than belt driven it could be the seals.

I think anything else not involving coolant is unlikely unless you've been doing something strange with a hose pipe.

Richard
 
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any physical external source dripping water onto a critical part of the engine e.g.oil level stick ? Highly unlikely but got to rule out e.g. washing the boat.

Is the sea water outlet side flowing freely ? If reduced flow for any reason, the water pump could be pushing sea water under pressure . Were coolant temps OK ?

Puzzling that the cause is not consistent and has not duplicated the emulsion effect.
 
single said:
At the weekend i checked the engine over before a planned 6hr motor and discovered water in the oil. The dipstick was grey but still oil viscosity like, but the filler cap was like grey yoghurt. I did a few oil/filter changes and all looked good so went off cruising checking it every hour. All is still perfect after about 8 or 9 hours running so what caused it? The fresh water side of the engine hasn't lost a drop so it must have been sea water. The exhaust has an anti-syphon valve fitted. If while cranking i had filled the exhaust, surely it would have hydraulically locked the engine? Maybe the jabsco seawater pump seals leaking? Any other suggestions? (Thornycroft T-95) Ps. On the first oil change there was about 0.5ltr of 'extra fluid' in the sump.
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If the seawater pump is, as Richard says, directly driven , as opposed to being belt driven, leaky seals are a possibility but there is usually a weep hole between the seals from which a small leakage will escape and hopefully alert you before any harm is done.

If your anti siphon device is a valved type, as opposed to being a peeing type, check the valve for correct operation. If it is the peeing type be sure it is peeing freely.

If you crank the engine for a prolonged period shut off the cooling water intake seacock.
 
I had a very similar problem with my Perkins M90. I found that the oil cooler was weeping seawater into the oil.

The raw water circuit has an anti syphon loop that meant there was a constant head of pressure on the sea water in the engine. The bottom end of the cooler bundle had some corrosion which I think was allowing water into the oil.

I stripped it down and replaced the "O" rings and so far so good. I did take a lot of flushing out to get the last vestiges of emulsified oil out of the system but I used a diesel engine sump cleaner from Halfords plus some cheap oil.

So far so good. This was about two years ago...

cheers,
 
BTW, I think the raw water pump is highly unlikely cause as the pump bearing housing is separated from the pump itself with a gap that allows leaking water to drop away without going near the engine itself.

cheers
 
DickB said:
BTW, I think the raw water pump is highly unlikely cause as the pump bearing housing is separated from the pump itself with a gap that allows leaking water to drop away without going near the engine itself.

cheers
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Some pumps have a large opening that as you say allows water out before it reaches the inboard oil seal. However some only have a small tell-tale hole that may not be big enough to take all the flow and additionally can become blocked with grease, paint flakes and general grime.
 
Its been run a lot again today and the oil is still perfect.I can't see any 'tell tale' leaks from the pump but i'm tempted to change the seals and bearings anyway (the engine has done 1200hrs since i bought it new)
It doesn't have an oil cooler so i reckon the pump it the only place water could get in.
 
I had massive amount of water leak into my engine due to previous owner making a total "horlicks" of rebuilding the seawater pump a few weeks before he sold the boat to me.
So, be careful when rebuilding the pump, make sure you do not nick the seals, ensure that the seals are fitted with a gap between them to allow any water leaks out through the drain hole and of course, make sure they are the right way tound.
 
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