Is diesel oil always black instantly?

[ValiantV]

Hi cruisers,

Been working on gas engines for years, but new to diesels. I've always heard that crankcase oil in diesels is pretty much black right away because diesels create more unburned carbon than gas engines. I have no idea if that is truth or urban legend.

Having bought an older boat, and this, no real idea how often the POs changed oil, mine is black now.

With a "dirty" gas engine, performing a couple of short-interval oil & filter changes can often clean out the gunk and leave you with oil you can see through for several thousand miles. Is this possible it even normal for a diesel?

I figure I'll do a couple of closely-spaced oil/filter changes anyway, but wondering what to expect. Any insights would be welcome!

[transmitterdan]

For many older diesel engines it is true. The oil turns black as soon as you start after an oil change. But for newer engines with good rings and tight tolerances it is not always true. My Yanmar 4JH3E with 2K hours has clear oil on the dipstick. But each year the oil i pump out of the bottom drain valve gets a little darker. Still it does not go instantly black like a lot of diesels do.

[Mike OReilly]

Mine is. Even after we had engine problems that demanded rapid-succession oil changes; six or eight over a week or so, it still turns black pretty quick. Mine is an older Perkins 4108 with 1200 hrs.

[Stu Jackson]

Add that diesel engines in boats are not like cars that can be put up on a lift to drain the oil. Engines are at an angle, and not all the old oil can be removed. Black: Universal M25, 3,200 engine hours, owned 19 years since 888 engine hours, always been that way.

[ValiantV]

Originally Posted by Stu Jackson

Add that diesel engines in boats are not like cars that can be put up on a lift to drain the oil. Engines are at an angle, and not all the old oil can be removed. Black: Universal M25, 3,200 engine hours, owned 19 years since 888 engine hours, always been that way.

True, not being able to drain (as) completely as in a car means you start out with "mostly" new/clean oil. Still trying to find the best way to drain oil without making a mess.

[model 10]

[QUOTE=Stu Jackson;2433213] Engines are at an angle, and not all the old oil can be removed.

Ours is almost level and the drain fitting is at the bottom, it still turns black. There is a lot of residual black oil all over everything inside the engine, oil cooler, hoses, passageways etc. I could get our Perkins oil looking OK but I would need to change it every 25 hrs and I go over 100.

[sailah]

My Westerbeke has a factory tube coming up from pan. I rigged a fitting to screw into tube and hook that to a hand pump. Extract it all thru that. The only issue is that since I have a V drive and engine is reversed, it's a real bear to reach.

Once I start sucking air, I dump 1/2 quart or so of new oil and let that sit. Pump until I suck air. Refill etc.

The little hand pump works ok, and was a cheap HF job. But the problem is now storing it. In a plastic bag it leaks the residual oil and now the pump is coated.

I think my plan will be to buy a 12v gear pump next year and mount that to engine room wall. Will set up a small manifold to allow pump to pull from engine and another "wand"

The wand would be for my transmission fluid which has no option but to drain into fiberglass engine tray liner thing.

But I've been lazy so far and have not set it up yet. A poor mans Reverso if you will.

"This year is the LAST year I'm dealing with this stupid pump!!"

Said me 3 years ago

Any yes, my oil is black almost instantly.

[belizesailor]

Yep, particularly older marine diesels, almost instant black.

Related experience. We bought a Toyota HiLux ashore, small efficient clean diesel engine, had oil changed. Checked it a few days later and it was so clean I could not initially see it on the dip stick...stayed this clean for weeks! Definately not what Im used to.

[sailorboy1]

So people are looking at it wrong. The oil is black so can see the level on the dipstick

[Cheechako]

It turns black pretty quick. But some do it faster than others. My Yanmar didnt turn that black very fast for some reason.
I think the flushing is a waste of time.

[a64pilot]

It's soot, and it turns the oil black from blow by past the piston rings. Much higher compression of a Diesel naturally leads to a little more blow by than a much lower compression gas engine.
Odd in my Yanmar doesn't turn it's oil black very quick either, but almost all other Diesels I've had did.
Oil turning black quickly is also indicative of a good oil, a good oil cleans out an engine and holds the soot in suspension, not letting it settle out into sludge.
I say that as I've often heard people say Rotella and Delo are not good oils cause they turn back so quickly, where in truth the opposite is true.

Flushing can't hurt, especially if you suspect the PO didn't change oil as often as they should. Rotella T6 synthetic would be an excellent oil to clean things out as it is very high in detergent, but it does cost a little more. I'd run it 25 hours and dump it, then 50 and change every 100 from then on.

[boatpoker]

Depends on the engine. My 40yr old Perkins HT6-354 turbo with 20,000 hours on it took about 30 hours for the oil to turn black. My TAMD 60B turbo also took about 30 hrs. while my Westerbeke 55A natural takes about 10 hours.

[ValiantV]

Originally Posted by a64pilot

.

Flushing can't hurt, especially if you suspect the PO didn't change oil as often as they should. Rotella T6 synthetic would be an excellent oil to clean things out as it is very high in detergent, but it does cost a little more. I'd run it 25 hours and dump it, then 50 and change every 100 from then on.

My thoughts exactly.

Though flushing - or even timely changes won't undue excessive wear or corrosion caused by earlier neglect - it can help to remove some if the built-up crud that the old oil's overwhelmed detergents and dispersants have left behind.

Aside from the added labor, the cost is pretty insignificant. Maybe $30 for quality oil and filter? I'd invest that a few times over for a little peace of mind and some degree of confidence that an expensive engine is operating under the best conditions I can provide.

[gamayun]

Good question. I've always wondered about this too

[a64pilot]

Now, once flushed out if it's an older design, naturally aspirated engine, may well be that straight 30W or 40W will be every bit as good as the syn oil, and the money you save use to change more often, don't buy into that it's synthetic oil, you don't have to change it very often.
We change oil in our little Diesels not because it's broken down, but cause It's loaded with soot and soot is carbon, and carbon isn't a good lubricant