gear box oil loss

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joeh

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my volvo MD6A suffers a loss of oil from its gear box.
about 0.2 litre( half the oil capacity) after say 20 hours of motoring
there is no visible oil smudge around the associated area
any suggestions as to what is the cause ?
ta
 
Unusual to lose gearbox oil without an apparent leak.
I'm not familiar with small boat engines except in lifeboats, so I'm guessing here, but the oil must be going somewhere; if it's directly coupled to the engine it could be migrating to the sump through a defective seal.
If there's a gearbox oil cooler it could be leaking into the coolant, but you might also get coolant contamination of the oil.
Only other place I can conceive of losing gearbox oil is through a defective seal on a CPP (Controllable Pitch Propellor) installation as fitted in many ships. Probably not relevant here??! /forums/images/graemlins/smile.gif
Good luck!
 
good point
but the problem is that the engine is also losing oil at couple of places which i can see.
the net effect is that the main engine lube level decreases a little.
i think as paul suggested its a defective seal
 
There is no oil pressure in this gearbox as its purely mechanical, so unless the breather is blocked the cooling water will always be at a higher pressure and would contaminate the oil.
I suspect the front seal is leaking and it is going into the engine sump and it is being masked by the engines own leaks.
 
MD 6A is now an old engine and past its sell by date and owes the boat nothing
there are likely to be a few old units about to use as spares rather than tring to repair but you are likely to have to replace the lot soon so dont be tempted to start spending much on it

There is not an oil cooler in the normal manner for this gearbox
if the reduction gear is fitted then it is enclosed in a water jacket with a flow from the water inlet the support bearing for the red gear runs in this casing which has a failry thin wall which can frost crack if the water is not drained
check for signs of emulsion in the oil

the gear box has a drain plug for the oil which can leak along with the input and more commonly the output seal as the outer surface of the red gear can pit quite badly if the dust seal (if fitted) fails
if the leak is constant and liveable with then it may well be best left alone
 
I've been a professional marine engineer for over 25 years, but it's still great to hear from people who really know their stuff.
/forums/images/graemlins/smirk.gif /forums/images/graemlins/smirk.gif /forums/images/graemlins/smirk.gif (Have a virtual beer on me gents)
(Education's a great thing, I must get one some time!)
 
My Hurth box lost oil steadily, with no sign of an external leak on the box itself. It turned out that it was the input shaft oil seal. Removing the box involved lifting the engine and unbolting the bell-housing, but seal replacement was simple. The inside of the bell-housing, ring gear etc. were very oily.
 
thk u all
since the engine is already out of the boat and in the workshop
i will dismantle n replace oil seal
 
Just a suggestion,as it's in the workshop already you might as well pressure test the cooling system as well, nothing complicated - maybe just blank off the outlet and connect a filled, elevated hose to the inlet. If the level in the hose drops over a period of time, you have a leak.
Just how teed off would you be if you put it back in the boat and found the problem recurring?
 
My Hurth gearbox was losing small amounts of oil sometimes but other times it lost none. I could never see where it was going. Eventually tracked it down to a blocked breather hole in the filler plug. When the gearbox got very hot it pressurised and forced a small amount of oil out, probably through a seal. Since clearing the breather hole I have had no oil loss for two years.

Plum
 
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