I have a 17ft Plymouth Pilot powered with a Volvo Penta MD1B engine fitted with the mono shift reverse gear and reduction gear.

The engine is fine but I've noticed some whitening of the oil in the reverse gear housing which tells me there might be water getting in there.

For reasons I have never understood the reduction gear housing has a water jacket round it and is in the cooling system between the sea **** and the water pump. So sea water is drawn in via the sea ****, goes round the reduction gear water jacket and then to the water pump. I suspect that the reduction gear water jacket is leaking sea water into the reverse gear housing.

I do not understand why the reduction gear housing needs to be cooled, especially on my 17ft boat with a max speed of 6kt, and I'm thinking of bypassing its water jacket and taking the sea water supply from the sea **** directly to the water pump.

So this is to ask if anyone has ever actually done this with the MS reverse gear and if so was it OK?

I'll probably try the bypass and then just chug around the harbour for half an hour, albeit at regulation slow speed, to see if the reduction gear housing gets hot.

Any thought most welcome.

 

Pull a sample of the gear oil and send it out to be analyzed. Get a oil analysis kit at NAPA for around $16.00.

 

Thanks, yes I thought of getting the oil analyzed, my local chandlery provides that service, but it's pretty certain to be sea water contamination.

I found out since that this is quite a common problem with these MS reduction gear water jackets. One person who had exactly the same problem as me has had the water jacket on his reduction gear bypassed for 18 months and hasn't had any problems with it. He reported that after a continuous 2˝ hour run at 2500 rpm the reduction gear housing was not even warm which kind of supports my question - so why the water cooling?

Anyway, I'm confident now that I can do the same.

Thanks again for your advice, much appreciated.

 

MY other concern would be if water can get it then it's possible gear oil can get out into the water jacket.

 

MY other concern would be if water can get it then it's possible gear oil can get out into the water jacket.

 

Yes I agree.
I have now bypassed the reduction gear water jacket by taking the sea water inlet directly to the water pump and I've capped off the water jacket inlet and outlet ports..
I'll be keeping a careful eye on the gearbox dip stick before and after each trip and on the temperature of the reduction gear casing!

 

Just to add a final post script to this thread, I took my boat out to sea today with the reduction gear water jacket bypassed as explained above.

I motored out for about 30 minutes then stopped to check the temperature of the reduction gear casing and It was warm to the touch but certainly not hot..

I motored around my bay for the afternoon, stopping and fishing then moving on, and then motored home at about 3/4 throttle.which took around 30 minutes.

When I stopped the engine on my mooring I let the oil settle for 10 minutes then checked the gearbox dip stick and it was still right on the full mark.

So my conclusions are it's OK to bypass the reduction gear water jacket on a Volvo Penta MD1B engine for fairly short motoring periods and if it was sea water contamination of the oil in the gear box coming from a damaged reduction gear water jacket, then it doesn't seem that the gearbox oil is leaking back into the water jacket.

Hope this helps anyone with the same issues.

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