Diesel engine oil becomes black ...... or not

Momac

Momac

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A friend has Yanmar 6 cylinder 250hp engines and he says the oil remains fairly clear.
In my Volvo Penta the engine oil gets very black.
Is this normal and if so why is there a difference between the two engine makes .
 
MartynG said:
A friend has Yanmar 6 cylinder 250hp engines and he says the oil remains fairly clear.
In my Volvo Penta the engine oil gets very black.
Is this normal and if so why is there a difference between the two engine makes .
Click to expand...
My guess it's carbon, plus there are different kinds of oils some clean the engine so it could be crud that's cleaned out from your engine.
 
It's normal for it to go black in a diesel

The oil goes black within a couple of minutes of running with your Vp because their is 2 to 3 liters of used(old) oil in the high pressure oil system, and a smaller amount in the low pressure system that does not get changed when doing a oil change. when you run it the new and remaining old oil mix, giving you the appearance that the oil is already dirty. The original source of the "black or dirty" looking oil, is from the blow-by of soot from the exhaust past the piston rings. Their are probably more reasons but I would say those are the main reasons.
With the Yanmar a greater % is recovered @ change -less black dilution of new to start with ,and may be less blowby of sooty stuff down the rings -- so it keeps it "yellow ness " for longer .

Detergent power of the oils may be different -- are you both using the same ?
Hours may be different between changes .
Volvo may take longer to get to operating temp than the Yam .Rings are designed loose when below op temp and become tighter and more resistant to soot contamination as they expand with heat --- all designed in
Who gets up to around 3000 rpm 1st and after how long bimbling about with cold rings ?
Yam may have better EDC or similar lests call it "electro twackery " that better regulates the fuel injectors ,minimising potential over fuelling ( when out side op temp ) thereby creating less "soot " to escape in the 1st place .
In other words the Vp has a crappier pump and control unit compared to the Yam .

loads of variables

Don,t worry about it .
 
Thank you for the detailed explanation.
The Yanmar is using the cheapest available fleet oil.
I don't know what I had in last time but must be okay as supplied by a reputable engineer. This time I have used Shell Rimula RT4X.
The oil changes have been by the book every 100hrs .
I am not worried just curious.
 
I was discussing just this with a VP engineer yesterday. I'm planning to do the annual engine service next weekend, but noticed when I checked the oil on Saturday, that it was dirty but still a golden colour. Normally it is black.

It really looks like it doesn't need changing, but will do so all the same.

Last year I used the normal Volvo Penta VDS 3 stuff. Will use the same again his year and see what happens......
 
I remember an occasion when this issue came up on here before and Latestarter pointed out, albeit with more detail, that the oil coming out black means it is doing its job.
 
when we change the oil in our generator(s) every winter, this is surprisingly clear !
we don't run the genny's much at heavy load, but run them for quite some hours every season (don't remember how much)
they are 25years old ! and have total +4000hrs each !
Brand is coincidently Kohler -Yanmar .(4cyl 17Kw)
 
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