Diesel gen question

[labrador]

Since this is my 1st diesel boat, I'm kinda a novice on certain things. Always thought that oil in diesel engines turns black right away after changing it due to carbon in the cylinders. On my mains, this happens after an oil change after running for a few hours. then when checking oil before going out again oil looks black. Had a guy working on the boat and had him change the oil while he was there a few weeks ago. Mains oil looks black as expected after about 20 hrs. Gen has about 45 hours since the oil was changed and looks as clear as if it came out of the can. Gen is a Phasor 8.5 with a Kubota engine with about 550 hrs on it. I'm not complaining by any means, just asking if this is normal?

 

[bobk]

My Westerbeke engine as well as the previous Kubota driven Onan also stay 'clean' between changes.

Bob

 

[Boatsb]

Not every diesel turns the oil black. detroits are famous for it but my onan ( 1972 vintage) does not.

 

[REBrueckner]

Ditto for my 8V71TI Detroits and 1972 12KW Onan ( black, not black, respectively).

I've always wondered what it is that causes DD to turn lube oil black...and so quickly....I believe my earlier 53 series engines also turned oil black.

I wonder if it has anything to do with DD two cycle design....

 

[SeaEric]

All of my previous Mercedes diesels oil turned black in 2 minutes. I always wondered about that myself.

 

[yachtsmanbill]

Dont forget about all the old oil in the galleries, pumps,coolers, etc... ws

 

[madhatter1]

My 98 Cummins turn the oil black as soon as they run just like my Dodge trucks. I had a 73 Bertram with 871TI's that were clear as new no matter how many hours run. Shell rotella in both so oil was not the difference. I dunno.

 

[Nonchalant1]

Higher compression diesels turn oil black faster. Gen's are lower compression, never turbo and never run at high RPMs. They turn a constant RPM (1650 or so?) to produce constant 60 AC cycles. Maybe those differences explain it.

 

[Canuck Dennis]

Kohler makes a 20 KW genset with 3 cyl turbo charged Yanmar engine, I have one...no problems, no relays, has PC board.

 

[bigbill]

in my 450hp turbo john deeres, the oil stays clear until change 200-250hrs

 

[rsmith]

Dont forget about all the old oil in the galleries, pumps,coolers, etc... ws

I didnt realise until I pulled the pans when I RB'd the 12'vs that there was a baffle that holds back almost a gallon of oil from draining out of the back plug. I pull the forward plug out now too.

 

[MikeP]

Turning "black" has no affect on lubrication nor is it any indication that the oil is "dirty" and needs changing. Any oil used in a gas or diesel engine will turn black at some point. Whether it happens in 5 minutes or 6 months is of no concern. If you believe it's a problem, just do an oil sample. You'll find no correlation between "black" oil and "bad' oil.

"black oil" is a ploy commonly used to get you to change oil when there is absolutely no need for it.