View Full Version : MD11C MSB Gearbox oil loss

06-29-2009, 04:53 PM
"I have a MD11C with MSB gearbox and heat exchanger. When I bought the boat 5 years ago, the previous owner old me that I would need to add 1 1/2 fluid ounces of oil to the transmission every 6-10 hours. He was correct. I have tried finding where the oil is going - unsuccessfully. Even some good local Volvo mechanics can't find it. It has been suggested it might be a blocked breather - but I can't find a breather on the MSB. I wonder of it could be flowing through directly to the maon crankcase sump. There seems to be an extremely fine "aerosol" type spray of clean oil over the top of the oil filter and each time I change the filter it gets covered again - so some oil is definitely leaking... I just can't find where. Any suggestions or ideas?"

06-30-2009, 10:17 PM
Only two places your oil can be going due to the design of the box.
Your ( MIST ) would make me want to look at the input shaft seal. I would think this will be the cultprit .If all looks good -- oil cooler.

07-04-2009, 04:13 PM
I had the same problem on my MD11 with MSB gearbox (raw water cooled) except for the oil mist on the oil filter. On mine I replaced the the O ring that seals the plug on the input shaft along with the input shaft seal. The bad news here is that you have to remove the gearbox to get at either of these. If you do this in the boat be careful when you remove the gearbox from the engine as the cavity between the two will be full of oil. Ask me how I know.

07-11-2009, 12:35 PM
"Since my last oil change [and previously], I have been somewhat convinced that the oil level on my sump [not geabox] was slowly rising. Yesterday, I decided to remove whatever oil necessary to bring the oil level back down to the top bar [ie. max] on the dipstick. I was shocked to discover I took out two litres of sump oil! A half gallon! I guess I now know where the gearbox oil has been going. Is it a major project to replace the seals between the gearbox and crankcase?"

07-11-2009, 04:24 PM
"There is no seal between the transmission and the crankcase. If the transmission is leaking out around its shaft seal, perhaps into the crankcase. just guessing."

07-12-2009, 10:14 PM
Thanks Joe but I don't understand.... how can there be no seal between the crankcase and the gearbox? What stops the oil from going between them?

07-13-2009, 11:02 AM
there are different seals. the transmission is a fully enclosed unit. the seal I am referrring to on the MD11C which might be expected to hold the oil in the crankcase when you remove the transmission does not exist. ergo when you remove the transmission the oil empties into your bilge