"Capt. JG" wrote in message
...
It's been a while since I checked the condition of the engine oil on my
Westerbeke 13... last time was at purchase.. about 18 mos. ago.

An old oil sample was sent off for analysis as a condition of the
purchase, and nothing out of ordinary was found, but I changed the oil
anyway.

I'm thinking that it's that time again, and I was going to send away to
have a sample tested when I ran across this article. It's a heck of lot
less expensive to test it this way vs. the $45 the last time for a
one-time test.

Has anyone done this? It seems to be fairly new.

http://www.marinelink.com/Story/Engi...st-210344.html

That test shows only contaminants and I see they include carbon.
Carbon will always be present in the sump oil of a diesel to some degree so
this test is usually going to show it up..
.. The main reason for regular oil changes is that modern oils contain
additives that hold carbon particles in a colloidal
suspension,which is why the oil in a diesel turns black.
If you do not change the oil at specified intervals the additives become
exhausted and the carbon load being held in the oil starts to fall out of
suspension and cook itself onto the pistons, rings and cylinder walls and
form sludge in the sump.
So prolonging the period between oil changes meansyou save a bit on oil
costs and your maintanance bills are much higher.
How easy is it to remove cylinder heads and/or draw pistons from the engine
in your boat?
I change my oil at the end of every season for this reason regardless of
hours run and always well before the engine makers recommended hours.
It pays off in the long run. My engine never has used oil in it during the
cold winter,when acids,water or anything else can condense and start
corrosion
or other problems.