Darkening of diesel oil

jcummins · Mar 17, 2014

I've used Rotella 15w-40 in all of my current diesel vehicles. Duramax, M7040, ZD326, JD Gator 855D. The Duramax I've had since new 2002. I've got 230K miles on it with no oil related issues. The oil in it, darkens gradually after an oil change, and is black at 5000 miles, my oil change interval. The ZD326 oil is black only hours after the oil change, same with the 855D, and kind of thought that's the way it was with diesels. The M7040 I bought last fall, 2007 model, which only had 280hrs on it. I've put 20 hours on it since then. Checked the oil Saturday....clean as the day I change oil. It's acting more like the truck.

What's the good, bad, or indifference to this?

juddspaintballs · Mar 17, 2014

The vehicles that the oil darkens quicker on allows more soot pass by the pistons while burning the fuel. The oil catches the soot and darkens. That just means the tolerances in your M7040 engine are still tight

Soundguy · Mar 17, 2014

yep.. black is mostly soot.

a dirtier engine will darken new oil faster than a clean one too.

diesel lover · Mar 17, 2014

juddspaintballs said:
The vehicles that the oil darkens quicker on allows more soot pass by the pistons while burning the fuel. The oil catches the soot and darkens. That just means the tolerances in your M7040 engine are still tight

Nice explaination!! On our 1956 massey ferguson with a perkins diesel the oil darkens pretty fast! Maybe 100 hours its turns pretty dark. Im a full time truck mechanic and I see it more with older trucks than newer trucks.

buickanddeere · Mar 17, 2014

A non issue and nothing to worry about.

The Fred · Mar 17, 2014

Oil will darken in half the time if you are using old high sulfur fuel like I am.

Some piston/ring designs allow more soot to pass by. If the engine is over fueled or normaly smokes black the oil will dirty much quicker.

Fred

DeereMann · Mar 17, 2014

The EPA Tier II & III reduced exhaust emissions engines had severely retarded fuel injection timing to get the exhaust NOx level down. To make up for lost power they opened up the fuel rate. This fueling recipe caused high soot loading of the fuel (fuel dilution too) from more piston ring blowby. You really gotta watch your oil change intervals on those engines, because as soon as the oil's ability to carry soot in suspension is exceeded, the soot plates out & acts like an abrasive wear agent on the finely machined parts (cam shaft lobes, lifters, fuel pump plungers - if oil-lubricated - etc.).

When they went to EPA Tier IV, they re-set the fuel injection timing back to advanced setting, then dealt with the higher NOx in the exhaust with cooled EGR &/or SCR + DEF catalyst in the exhaust pipe. So at least the mileage came back with Tier IV engines, and not so highly soot-loaded either.

jcummins · Mar 17, 2014

Hmmmm....I just went and took a check of my oil in the Duramax. This truck I bought new 2002....it's a 12 year old truck with 225,400 miles on it. Don't use much anymore, but probably will never sell it. It has 2000 miles on this current oil change. The oil is med tan. It uses no oil. Motor has never been touched, except for injectors. It has a 180hp chip in it (although I don't run on the high setting) since near new. The oil gets dark, but only after 5000 miles and not as dark as my ZD326 and 855D is right now. The ZD326 is not even close to be due for an oil change, the 855D I will change in couple of months. The M7040 is 7 years old....but, the guy I bought it from hardly used it, one of the main reasons I bought it, only 295hrs on it. Maybe it will act like the Duramax.

So....tolerances in the Duramax still tight with 235,400 miles? Perhaps, but it's done some hauling, hay, cattle, fifth wheel (heavy one too). It blows black on cruise at 70 mph with that fifth wheeler. There is something very different in the way these motors have been built. Most likely the EPA is the culprit too.