Oil still dirty after change?

VT Fitz

VT Fitz

.
Oct 19, 2006
337
Hunter 27-3 Brownsville, VT/Mystic, CT
On Monday I performed my first oil change on our '07 Hunter 27-3, Skaði, and was a bit surprised by how black the dipstick remained afterward. When I change oil in the car, it's not at all black.

Our little 15 hp Yanmar (2YM15) only takes about 2 qts, so perhaps when you mix with what's left in the pan, it isn't getting diluted as much as a 4-5 qt change for a car. Still, while it was certainly better than when I started, it was pretty dark.

Or perhaps I didn't let the engine warmup enough to be able to pump out the sludge at the bottom. I was concerned about it getting too hot because the pump warned not to handle oil over 140 degrees.

I also had a great rookie mistake... I didn't remove the fill cap, so it was a slow and painstaking process to pump the oil out! Doh!

Thoughts?
 
Ron20324

Ron20324

.
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
If you ran the engine right before draining, you've left "a lot" of oil in the engine that takes a while to drain down. If you have run the engine in recent days, the oil has a chance to drain all it can back to the crankcase, Then again, some oil can pool up in the nooks and crannies of the engine and never drain back, but will be picked up when you run the engine after changing the oil. Me, I prefer to suck to oil out when the engine is cold. Yeah, it is thick, but in the summer months it is not all that much effort. Others will have their own opinion, and this is mine.
 
FastOlson

FastOlson

.
Apr 8, 2010
2,115
Ericson Yachts Olson 34 28400 Portland OR
After doing annual oil changes in our three-cylinder diesel for over 20 years, it is apparent that some old "dirty" oil always remains in the engine after a thorough/patient removal. The ultra-fine carbon particles in what's left instantly mixes with the new oil and in appearance is Black... again.
:(
Our engine is in good condition, and does not need any added oil between changes, FWIW.
I would prefer that, like my vehicles, the new oil would stay clean after the change, but ... reality is what it is.
FWIW, we do have the pan drain plug hose leading up by the engine, so we do get most all of the four quarts out when doing a change -- there would still be an ounce or two sitting behind that plug area due to the slight down-slope of the mounting scheme, but there's not much there. My vacuum oil changer tank holds one gallon, and it fills up very close to the mark when evacuating the old oil.
Are you able to drain from the bottom of the pan, or do you have to suck it out via the dip stick tube?
 
C

Capt jgw

.
Feb 8, 2014
1,300
Columbia 36 Muskegon
You can never get all the old oil out through the dipstick, so what's left turns the new oil black. It's really not a problem though, it's just a little bit of the old. Draining from the bottom is better, but Yanmars (at least the ones I've worked on) don't have drain plugs.
 
Alan Gomes

Alan Gomes

.
Nov 22, 2011
1,250
Ericson 26-2 San Pedro, CA
VT Fitz said:
On Monday I performed my first oil change on our '07 Hunter 27-3, Skaði, and was a bit surprised by how black the dipstick remained afterward. When I change oil in the car, it's not at all black.

Our little 15 hp Yanmar (2YM15) only takes about 2 qts, so perhaps when you mix with what's left in the pan, it isn't getting diluted as much as a 4-5 qt change for a car. Still, while it was certainly better than when I started, it was pretty dark.

Or perhaps I didn't let the engine warmup enough to be able to pump out the sludge at the bottom. I was concerned about it getting too hot because the pump warned not to handle oil over 140 degrees.

I also had a great rookie mistake... I didn't remove the fill cap, so it was a slow and painstaking process to pump the oil out! Doh!

Thoughts?
Click to expand
This is totally normal for a diesel. Don't worry about it.
 
  • Like
Likes: silverbeard
Rich Stidger

Rich Stidger

.
Feb 10, 2004
4,134
Hunter 40.5 Warwick, RI
I have two diesels. The Volvo auxiliary has a drain hose internally connected to the pan and when I change the oil in that engine the new oil is the normal golden color- and it seems to stay that way, only darkening slightly.

My Westerbeke genset has a hose that is connected to the bottom of the pan externally. After changing that oil the new oil instantly turns black.

No explanation that I can find to square this observation.

I wouldn't be concerned with the oil color.
 
Don S/V ILLusion

Don S/V ILLusion

.
Sep 25, 2008
7,435
Alden 50 Sarasota, Florida
This is duplicative but to confirm what others have already stated, we have two diesels. One car; the other being the marine diesel. In this context, the distinction is the former has an oil pan drain.

The car oil is clear immediately after changing while the marine is never indicative of the ineffective removal of dirty oil via sucking from the dipstick.
 
Justin_NSA

Justin_NSA

.
Jul 7, 2004
8,492
Hunter 30T Cheney, KS
VT Fitz said:
On Monday I performed my first oil change on our '07 Hunter 27-3, Skaði, and was a bit surprised by how black the dipstick remained afterward. When I change oil in the car, it's not at all black.
Thoughts?
Click to expand
Had you run the engine before you pulled the dipstick or just put it in and take it out? If the former, I'd agree it's normal. If the latter, I'd say you didn't get enough oil out because the new and old really shouldn't have been able to mix that thoroughly yet. My interpretation anyway.
 
C

Capt jgw

.
Feb 8, 2014
1,300
Columbia 36 Muskegon
One of my commercial vessels has V92 Detroit's running 100% biodiesel. The oil in those stays remarkably clean, about what you get in a gas car engine at 3000 miles. It actually makes it harder to check the oil, you can barely see it on the dipstick. At least the black stuff is easy to see.
 
B

Benny17441

.
May 24, 2004
7,173
CC 30 South Florida
By changing the oil you replenish the viscosity which is what lubricates the engine moving parts. Black oil just means there are particles in the oil that are too small to be picked up by the filter and hence are not harmful to the engine. Since we cannot get all of the old oil out there will always be a residue but irregardless even new oil will turn black rather soon. The point is that oil viscosity is the important part and that black oil is not harmful.
 
thinwater

thinwater

.
Mar 26, 2011
3,717
Corsair F-24 MK I Deale, MD
VT Fitz said:
On Monday I performed my first oil change on our '07 Hunter 27-3, Skaði, and was a bit surprised by how black the dipstick remained afterward. When I change oil in the car, it's not at all black.

Our little 15 hp Yanmar (2YM15) only takes about 2 qts, so perhaps when you mix with what's left in the pan, it isn't getting diluted as much as a 4-5 qt change for a car. Still, while it was certainly better than when I started, it was pretty dark.

Or perhaps I didn't let the engine warmup enough to be able to pump out the sludge at the bottom. I was concerned about it getting too hot because the pump warned not to handle oil over 140 degrees.

I also had a great rookie mistake... I didn't remove the fill cap, so it was a slow and painstaking process to pump the oil out! Doh!

Thoughts?
Click to expand
a. Diesels generate more soot than gasoline engines and the oil is much blacker for this reason.
b. I am certain your crankcase has a vent. This is required for proper operation. I would look for it. The filler cap is NOT the only vent.
 
VT Fitz

VT Fitz

.
Oct 19, 2006
337
Hunter 27-3 Brownsville, VT/Mystic, CT
Thank you all for the input.

It only took 10 years with our old girl, Grasshopper, to get to know her; now we start all over again with Skaði!
 
Last edited:
N

nveater

.
Feb 27, 2004
172
Hunter 335 North East, MD
As others have said darkened or black oil after an oil change is fairly normal- although mine seems to stay cleaner after have a lot of work done on the engine. Smell the oil on the dipstick if it doesn't smell burnt you are probably okay- if there is a burnt smell that could be indicative of a problem
 
M

mbatsea

.
Feb 23, 2011
8
Hunter 466 Singapore
I have a diesel genset together with my yanmar main engine. Need to suck the oil from both. After the change the genset oil is golden and main engine is not. Try as I might I cant improve the main engine. I seem to suck all the oil out that the manual tells me it holds. It does smell better than the old stuff... so I've concluded there is simply enough of the old in there to throw the color. But I'm convinced that any analysis would show that the oil is now >>99% new. So mission accomplished. You do of course have to change the filter.. which once or .. no just once.. I forgot to do.
 
Ron20324

Ron20324

.
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
mbatsea said:
...After the change the genset oil is golden and main engine is not. ...
Click to expand
Perhaps the Gen was designed without all the little nooks and crannies where oil can stand, rather than draining back to the pan.
 
You must log in or register to reply here.

Top Bottom