why does oil filter become black/colored?

[Nikell]

Hi all, first post here.

I've been reading about oil filters last days and it's ability to trapp/filter particles. There is one thing I can't get my head around.

Filters are often rated as to the smallest particles they will trap, for example 10um.
What I can read the soot which blacken the oil is around 0.1um(100nm).

Now, an engine oil filter gets black very quick, why is it so? shouldn't the soot just pass thru? Or, does it actually trapp single soot particles?
If it's the last case I would believe the oil filter to be quickly saturated for it's ability to trapp small particles?

 

[simple_gifts]

Are you referring to diesel engines?

I have never seen a black petrol filter.

 

[Graham Piccinini]

I know in gasoline engines (at least the 30+ that I dealt with) the color of the used oil filter media is directly proportional to the color of the actual motor oil. And the color of motor oil gets darker mostly for 2 reasons. Reason 1 is sludge, deposits, and contaminants. Reason 2 is heat. Certain additives in the oil's add pack cause the oil get darker through heat cycles, quicker or slower depending on the oil blender. When I pulled an oil filter with 2000 miles it was noticeably lighter in color as compared to the same filter from the same engine, but with 7000 miles. But so was the oil color.

 

[Kira]

"Sooty oil" still hangs on the fibers even if let to stand. This'll darken a yellow or tan element.
Ha, do the red ones turn maroon?
Also, the 10, 15 or whatever micron size particles are black too.

To the O.P: What is prompting you to read about oil filters?

Wouldn't it be horrible if the O.P. was "corona isolated" in a room with nothing but oil filter tech reports to read?

Our trip to Paris last March was so fun. A year before the virus and one month before the fire.

 

[BMWTurboDzl]

Don't forget that the filter media itself will retain oil. What you're seeing is a mixture of larger particles caught by the filter and particle suspended in the oil which is coating the individual fibers within the filter media.

 

[JohnG]

Even though filter media is rated at a certain particle size, they have a range of sizes that they can stop. No, automotive filters are not designed to stop 0.1um, but they CAN stop smaller particles on occasion.

Think of it more as a curve than just a straight cutoff point. Same with air filters, and there are plenty of test videos out there to demonstrate what I mean.

 

[mpack88]

I looked at some Quaker Steak 10 W 30 oil in the Saturn with 240,000 miles on the original engine that has been neglected and the oil turned dark within 500 miles. Almost like diesel motor oil. Meanwhile on my 2018 Taurus its motor oil still looks after 8,000 miles. Granted it's a new engine

 

[Job]

I changed oil recently and the oil looked light golden on the stick, and now sits black as coal in the recycling jug. Besides black caught particles as others have said, its the oil film thickness. Touch the filter and see what the thin film looks like, it will be lighter in color. You can see it on pictures here too the oil around on the filter base etc is lighter than a darkened filter element even with no visible particles..

 

[JMJNet]

Because it is a good filter.

If it does not become anything, means everything passes through including the contaminants.

 

[blupupher]

Originally Posted by BMWTurboDzl
Don't forget that the filter media itself will retain oil. What you're seeing is a mixture of larger particles caught by the filter and particle suspended in the oil which is coating the individual fibers within the filter media.

I notice this on filters that I cut open. The media appears very dark, but after I wrap it in paper towels to pull some of the excess oil out of the media, the media does not look near as dark as when saturated with oil.

As said as well, larger particles that are filtered out are also dark colored
Also the filtration numbers are usually based on a single pass, but after multiple passes, some of the smaller particles will be caught in the media as well.

And finally, just as the color of motor oil does not indicate oil condition, filter media color does not indicate filter load.