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Old 07-10-2013, 09:22 PM   #1
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Water in Thruster

I have a Dickson stern thruster that is filling the hydraulic tank with water.
I'm assuming the water is coming from the drive unit as that's the only thing in the water. There is no sign of fluid in the water (no oil slick). I've searched the www but can't find anybody selling repair parts. Can these be resealed/repaired? Anybody have experience with these?
Clay
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Old 07-10-2013, 09:35 PM   #2
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No experience with your trouble but if the seals need replacing chances are this outfit has them.

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Old 07-10-2013, 11:10 PM   #3
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There may also be an oil cooler and if so it could be leaking. Check carefully for one. It may be quite small and may not be obvious.

Why don't you contact Dickson:
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Old 07-11-2013, 10:08 AM   #4
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There may also be an oil cooler and if so it could be leaking. Check carefully for one. It may be quite small and may not be obvious.
I like the oil cooler leak, as this is a low pressure part of the system.
The fluid pressure in the actuator is going to be exremely high, not sure how water would be able to get through the seals with the high pressure fluid behind the seals.
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Old 07-11-2013, 03:56 PM   #5
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not sure how water would be able to get through the seals with the high pressure fluid behind the seals.

You wind on an old piece of fish line with the spinning prop.

Reverse direction does not remove it .
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Old 07-11-2013, 04:31 PM   #6
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not sure how water would be able to get through the seals with the high pressure fluid behind the seals.
Because the thruster only works about .00001 percent of the time it is submerged in water and the only time the housing is pressurized is when it is running. The rest of the time it is subject to a foot or two of water column.
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Old 07-12-2013, 12:26 AM   #7
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Does the unit currently function?
I looked at the unit on there website.
I think the water is coming from elsewhere.
If the unit is working there is no way for water to enter the reseviour.
Could you have a waterleak on the top of the tank?

Sd
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Old 07-12-2013, 08:53 AM   #8
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I think Rick is correct, when the unit is not running the outside water pressure is much greater than the inside hydraulic pressure which is zero. So water leaks into the unit.

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Old 07-12-2013, 09:12 AM   #9
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If water under very low pressure can leak in at the prop shaft it seems oil under pressure would leak or gush out. Is there an oil sheen after running the thruster?
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Old 07-12-2013, 09:31 AM   #10
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If water under very low pressure can leak in at the prop shaft it seems oil under pressure would leak or gush out. Is there an oil sheen after running the thruster?
The unit most likely uses lip seals which use the pressure of the fluid to aid in pressing the seal against the shaft. When the pressure on the inside of the housing is less than outside, fluid may flow to the inside if the seal or shaft is worn.

High quality units use a double lip seal to help prevent this from occurring. If the external seal uses a stainless steel garter spring that has corroded away allowing the seal to relax its contact on the shaft, the chance of leakage from outside in is increased.

Have the oil tested and see if there is a high sodium level ... if so then the seals are leaking or something is spraying seawater into the hydraulic tank vent.
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Old 07-15-2013, 08:32 PM   #11
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Pulled the boat this weekend and removed thruster. So I took it apart and there is a housing around the hydraulic motor itself. Housing was full of water and the o-rings around the fittings were torn. I managed to find 4 of 5 o-rings that kinda fit. It's working and not leaking, for now. It has no "lip seals" that I could see, I didn't pull the shaft out. but does use square o-rings. The unit is quite simple in design. What I don't get is how water can get in but not out. I,m hoping to get by until winter
then I can send the unit to Dickson and they will reseal it.

Boat is in fresh water. Thruster uses auto trans fluid. Fluid looks like strawberry milk.
thanks everyone
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Old 07-16-2013, 06:02 AM   #12
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It has no "lip seals" that I could see, I didn't pull the shaft out. but does use square o-rings.
That "square O-ring" is probably an X-ring, the lower cost manufacturing alternative.

It will probably still leak but since you are in fresh water it probably won't destroy the system if it hasn't already. Water in a hydraulic system is not a good thing.
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