T&T: Oily Alternator

[Milt Baker]

Steve,

I've owned four 6BT5M Cummins engines on three yachts over theyears, and I can 
confirm that the engines do spread a fine mist of atomized oil around the engine 
room.  You rarely see it in the air, but it settles on every horizontal surface 
and leaves a perpetually messy engine room.  

The easy (though not necessarily cheap) answer for me was to add a Walker AirSep
for each engine.  Once I did that, atomized oil was never again a problem.  More 
info at: http://www.walkerairsep.com/

No connection with the company; just a satisfied customer.

In my experience (roughly 12,000 hours total) the 6BT5.9M engines are terrific.  
One heads-up: my mechanic recommends replacing the tranmission oil cooler on these 
engines every 1500 hours, and I followed his recommendation and never had a 
problem.  A friend with the same engines didn't do that and ended up get-
ting salt water in one transmission; he had to replace the transmission--a big 
and expensive fix that could have been avoided.  

Good luck!

--Milt Baker, Nordhavn 47 Bluewater, Palm Beach Gardens, FL



Steve wrote:

Looking around my, new to me, 2003 Cummins 6bt5.9m engine I recently  found a 
bit of oil on the area under my alternator, I was surprised since there  are 
no oil using components, hoses, or seals anywhere around there. I figured  the 
previous owner or mechanic must have spilled some oil on it at some time.  
So, I took it off and had it cleaned and tested, everything was fine. Put it  
back on and a couple of weeks another drop or so of oil under it and the inside  
oily again, not much but damp, so I posted the question on Boatdiesel.com one 
of  the "Gurus" told me that a fine mist of oil is released through the blow 
by or  crank case breather tube and the alternator takes this in with it's fan 
and it  sticks to the insides of the alternator. I do get a couple of drops 
of oil  out of the breather tube but nothing in the engine compartment is oily 
or smells  oily. When I checked the air cleaner filter I did find a few tiny 
drops on  it.  I was telling a friend about this he has a similar engine  and 
was a bit skeptical and had never had the problem, but, when I put  my hand 
under the alternator on his engine it was oily also. 
You may want to check your alternators for this. The mechanic at my  
alternator shop told me it wasn't a fire hazard ( true or false?) but the  oil will 
make the brushes wear faster.
The Boatdiesel "Guru" has a fix for this, adding a collector and filter, it  
is complicated not to do but to explain if you find you too have an oily  
alternator you may want to search their site. I am traveling now but when I get  
the boat home I plan to do the modification.