Why Does Diesel Oil Turn Black? Why Is Diesel Oil So Dark? 

I bought a Mercedes 240D years ago. I had the oil changed at my mechanics and a few days later checked it and it was black. I brought it back and asked if he changed the oil. He laughed and said you never owned a diesel before have you. I said no.

After teaching maintenance and repair vocational classes for over 27 years, I have to say that your presentations are well done and easy to understand. A couple of years ago I bought a 2003 Winnebago diesel pusher with a Cat 3126 330 hp which is starting to give me some problems. Since I do a lot of my maintenance and repairs I have learned a lot from your videos. On the way home from a trip the check engine light came on and the the rv slowed to 45 mph, after a few minutes of this the engine power came back up and I could go normal speed. After stopping, shutting the engine off, and sitting for a few minutes I restarted the engine and drove another 150 miles without a problem. After arriving home a month went by I took the rv to fill it up with fuel and drove it back home - - no problems! I start it once a month and run it a few minutes at a high idle to keep it dried out and lubricated. The last time I did it when I brought it back to low idle and the engine started bucking and shut down and now it won't start. Thank you for the videos - - I am now doing the trouble-shooting according to your advice,.

Thanks for putting this up, I bought my first Diesel Car yesterday and while I decided to do a little check just to make sure the dealer had done what he said he would do, shock horror when I checked the dipstick and the oil was black....so on to the phone and he assured me this was normal and from watching this you have confirmed that I wasn't being duped... Thanks

finally the information I was looking for. I bought my first diesel car 3 months ago and just checked the oil for the first time. I was starting to get worried, Thank you for this video!

Awesome video, I'm about to start Diesel school in the fall. Your videos have been very informative!

just what I wanted to hear. Switched from gasoline to diesel after a 30+ years of caring and tending my cars with passion. My new car is still under warranty and I really had serious doubts had the service guy really done the oil change (very tidy or no job: no oiled areas around filter base, drain plug, nothing). The color of oil though HAS changed (lost the amount of black) but far from what I experienced from my gasoline cars. Thx again, just the amount of information I needed for a piece of mind :-)

Thanks bro! Got a 2019 ram ecodiesel and checked my oil when I finally got it home... Changed the oil immediately and after a ride around the block, my oil was black! Since it's Christmas, I'm obviously not able to get into a shop... Your video put me at ease! Thanks

It is just plain fun to view these intelligent, well presented videos. At the fleet shop of my current employment, I have the luxury of allowing engines to drain over night, which allows one extra gallon of old engine oil from a 3406E to exit the pan. That, coupled with proper maintenance intervals and converting to CAT oil filters (from the imitations), resulted in the new oil amber color remaining visible much, much longer, plus when the oil is due to be changed the next time, it isn't so thick and black as before. Prior to this approach, one could fire up the engine and not really tell if the oil had been changed. Unfortunately, that overnight situation is not available to dealerships and most fleet shops.

Thank you. We bought a "new" 2004 Kenworth with my son in law. Now, without all the logs, who knows how often the oil was changed? So first things first, the oil was changed. 2,000 miles later it was changed again and after 4,500 miles the oil looks new - no soot. Some one basically took care of the truck. I'm going to watch more of your videos. Being neither a mechanic nor a driver I need your educational videos. FYI, we did have some problems with the fuel filters and we did what I did with my boat - add some tank cleaner and change the filter, repeat the process and then cut down on the cleaner until the filter looks clean when you cut it open - which we did for six filters. Last filter looks great after 2,500 miles so we just need to put a protocol in the log book so it is done on a regular basis. I think this truck sat for some time before we bought it so we will maintain it as though maintenance was not done for a while. Again, thanks for your videos. My 32' offshore fishing boat is gas so I have little problems storing it over the winter - just some gas stabilizer and off we go. I could not afford diesels or the maintenance at the time - nor now that I am retired.Sent you an email with a question: Could you expect a Mack with 775,000 miles on it have a catastrophic exhaust valve failure when the Mack engineers increased the HP from 415hp to 485hp? I would still appreciate an answer. Again, thank you so much for the videos. I have spent 53 years fixing middle market companies but I am grossly ignorant about things mechanical.

Adept Ape, I always find your videos informative, thank you.

Excellent video! 👍👍👍 I agree much soot ending up in the oil is only a cosmetic issue since particle sizes are so small they are below clearances in rotating parts of the engine. Manufacturers have been observing dark diesel oil for a long time and if there was an issue effecting warranties ($$$$ for the manufacturers) the situation would have been dealt with long ago.

Short answer its a form of soot control in the engine and in capturing this soot it turns jet black and will "tattoo you" as lube techs say.

Thanks for the explanation. I just did an oil change on my Audi Q3 TDI and when topping up and checking dipstick I noticed the oil was already black. Only ever done oil changes on petrol engines before so that was a surprise. P.S. Subscribed.

Great explanation on diesel soot or My Dirty little Kitty Cat! Keep rolling those great videos.

My engine takes atleast 2000km to show some blackness in the oil. (Now it's not a truck but a 2.4D Toyota Hiace... which absolutely runs like a dream) Every 8000km there's an oilchange and inbetween there's a enginecleaner additive.... But therefore i also mix some engine oil with the Diesel too make the fuel richer again. I gues the engine is in great shape! Thanks for the video!

I’m starting school in February 2020 and these vids are so helpful for an insight on what I’m getting into

i did asways wonder why the oil did turn so black so quick,thank you for the info i can notch this off of my bucket list of things to know

I think this was an excellent vid. We just bought a 1 year old 2500 HD Diesel…. Dealership said “we did and oil change”…. I checked it was black about 2000 miles after… Was annoyed about it… found your vid apparently it’s normal after checking other resources…. Thanks makes sense. ! I’d never owned a diesel before this.

Soot actually is used as a pigment, they just call it carbon black. Look on any can of black rustoleum and you will see it listed as an ingredient. Thanks for the videos, you have a knack for explaining things scientifically accurate without bias, I am getting tired of people thinking they are diesel geniuses because they read how to turn up the fuel on their "cummings" engines in 8 lug magazine....!

Very thorough explanation, thank you. After I drain the old oil, I add a cheap same grade oil and run the engine to operating temp, then drain and add oem oil to get rid of as much soot as possible. I know it's a bit of a waste of oil during process but it's been so annoying to see a black oil straight after a change. And it's much still cheaper than taking it to a mechanic.

Thanks for sharing . 1st time owner of a diesel and was wondering why the oil changed so fast.

very good educational video. thank you for sharing your knowledge and for educating yourself first. major Kuddos and Respect!

Accurate info. And yes, there is a bunch of oil left in the gallery. I have a 2001 7.3 F-350 and I believe both heads hold over 2 quarts total. 👍

Great video, you made it easy to understand and the visual aids were a plus

I work at an oil shop, and just asked our tech this question yesterday when a diesel came in.

30 second vid... it is soot in the oil.

Nice informative video. I have 2 ,7.3 ford diesel motors. One turns black a short time after an oil change and the other is pretty clean looking even after 3000 miles.

I also wondering the same issue but thanks for your explanation

Like your style, clear concise and efficient. thanks.

Makes sense. I bored out a 360 to 366 and Rebuilt the entire thing. ran it with 15w40 diesel oil . its been 6000 miles and the oil is still clean as all hell. as to where out cat 3116 which we run with the same oil, gets dirty super quick. thanks for the video, man!

Very well explained.....

Excellent clear explanation, I've often wondered why that happens, thank you!

Very reassuring, thank you for taking the time to explain this 👍 👏

Th Y for a very good comment.

Great video. All your videos are very detailed and informative. Really enjoy your channel.

very true about all the oil not being fully removed. I always drain my oil hot and leave it over night to refill with new oil and by the morning the pan is still dripping out some oil

A local diesel shop (factory authorized by Mack, Cummins, Cat, and Detroit) has a regular customer. He runs compounds with add on lift pumps and more fuel mods than I can remember. It was an over-road 855 Cummins. When they ran it "full fuel" the oil consumption ramped way up. I theorized that since they were pushing so much fuel, the rings were not sealing and were actually floating between the rings and cylinder, thus more oil left on the cylinder walls. What do you and the community think?

Another thing to consider is that the full flow oil filter only filters out particles around 20-25 microns and larger, thus leaving all the smaller particles free to flow in the oil. In order to combat that, a bypass oil filtration system can be installed. These can filter particles up to 2 microns and smaller out of the oil thus giving it a cleaner look without the sooty look

Thanks for sharing this information and all the very best

Great vid mate Cheers 🍻

Good job on explaining for people who are not mechanical long for us who are lol , good job !

I got a Pete 389 with C15 SDPXXX, I service it myself with intervals of 11k -12K miles even though CAT recommends up to 30K miles. As you know these engines have the DPF system on them, and after a while they become pain in the butt, and break the bank account. I bought the truck with 470K on the engine, can't remember how many hours, but, it couldn't have idled a lot because there is an TK APU on it that I call a life saver. At first, I used to change the oil at a service station, and every time the tech used to show me the deep stick after a fill up to assure the oil level, the oil used to be gold color, and it took a while before it turned black. After a couple of DPF clean ups, I started having all sorts of problems from clogged filter to bad sensors ...etc. I had to take care of the dam thing once and for all, and I did. Since then, truck runs, and sounds like a totally different truck, and when I change the oil, I have a hard time checking the oil level because it's so clean, and it runs like that for few thousand miles before it turns totally black, I would say somewhere between 7-8 K miles, BTW, the truck has 960K miles, and about 23400K operating hours.

Thanks a lot for your explanations! I've some older Perkins engines around here (non turbo) with much idle time and the oil is almost instantly black. Now, I get why :)

Thanks for the post keep up the good work.

Thank you for video. So how can we understand the oil quality is good or bad?

Thank you for the explanation. I bought my first diesel truck about 6 months ago. (17 250). Had the first oil change done by the dealer (Ford), and then checked the oil about a month after and saw it was black. I thought that they messed me up and basically charged me for an oil change that they didn't do. About a month ago I decided to change the oil myself using the same Motorcraft oil they used. Filter was changed as well. I was thinking maybe I need to delete the truck due to the soot in the oil. I probably will do that anyway but now I can relax a bit regarding the oil as now I know it's a normal process with these diesel engines!!!

Thanks for the info changing my oil in my 6.7 cummins ...what about synthetic oil with a pro long Oil additive because that's what I have been using I have had good luck so far

Pretty good video. But I would have touched on how dirty looking diesel fuel looks vs gas vs propane . Obviously propane burns really clean and most oil change intervals can be extended vs diesel or gas . Great vid

I have just bought a 2009 Mercedes ml320 bluetec diesel engine it has 118,400 miles. I changed the oil and filter. It still runs like brand new. Used a 5w30 full synthetic oil. I also changed the transmission filter and fluid.

Thank for info that clears a lot of stuff up.

Thanks ! I was really wondering why my oil is allways dark even tho I change it every 10000 km ... ! Even tho the producer of the car says it should be changed at 30k km ...

Great video and explanation.

Thanks for the video. Now I feel less worried.

I own a truck trailer and perform a oils change every 40 thousand miles never problems, in winter weather apply 10w30 and Summer hot weather 15w40 working like a rockstar,

On another topic, I'd like your opinion on the use of fuel injector cleaner products such as Seafoam in the cat C7 engine.

What's your opinion on the automated manual gear box have driven them and hate it so slow to change and at a rounder bout it dose not know what gear to be in ,when you apply the brake the clutch disengages the time delay in so bad is this just a standard gear box and clutch with a air shift system ,automatic is far far better may cost more but worth paying the extra $$$ great videos keep up the great work thanks for down under

Can prevent black oil by using a engine oil bypass oil filter down to 1-2micron and reduced fittings to limit flow, Cat C-12 for example have these standard, they should do same for 15’s and 16’s, oil will stay amber with low micron filters. Side note : EGR quadruples soot load in oil

I had a 2000 pete with 99 550 cat in it an that was the cleanest running engine I have ever seen. It would take around 5,000 miles before the oil got dirty looking.

You'll get darker oil quicker during normal running and not idle, higher combustion pressure = more blowby and also more fuel injected to create soot.Also, combustion products create acidic mixture (especially if there's a lot of sulphur in the fuel) so its important to have a high TBN (Total Base Number) rating in your oil to make sure it neutralises this and keeps the engine corrosion free

The company I work for has 3 Kubota four cylinder 57 hp Diesel engines. One of them has a rough idle when warm and it sounds like it's running on two cylinders, but when it's revved back up, it runs fine. I don't see excessive amounts of soot billowing out the exhaust, but there is a thick lining of it in the exhaust pipe. It has close to 5,000 hours of use, and the air filter, oil and oil filter are changed every 400 hours. Would worn fuel injectors be the cause of the rough idle?

Maybe soot could be used to make printer toner? lol

bought a 6.5turo gm had a good mech but alas noone lasts forever didnt mid learning basics with gas motors eve rebuilt a few dpecils a new world thanks for the videoes learning a lot peace nick

This is an awesome video for educational purposes, thank you very much even if I'm 6 years late to the party

ck-4 and Fa-4 oil standard promise to improve oxidation resistance

Is it a good idea to add a cleaner before to do the oil change and thin it out ?

my mk5 golf variant from 2009 is producing soot while accelerating and i love it also the oil is pitchblack after a couple kilometers

Good info. In 1963 I put a toilet paper filter on my nearly new Rambler American flat head 6. Used Delo 100 W 30. The oil went from dirty and black to like new and stayed that way. I thought the same would happen with the Peugeot diesel. It wasnt going to happen.

Try a little bit of that orange hand cleaner to help your dirty work wear and oil spots before you put it into the washing machine. Works great!

Excellent video tutorial

all diesels ive encounted did this... except one, we have a Massey Ferguson tractor with several thousand hours on it, and it still doesnt create a lot of soot. Even when it comes time to change the oil, it always seems to look as clean as ever.

Centrifigual filters help alot with removing all the carbon/soot out of the oil

2012 Dodge Ram 2500 6.7 Cummins 215000 miles. ROTELLA 5W40 OR Valvoline 5w40 what ever is on sale at the local napa. Platinum filter 5000k change intervals. Oil is honey color at oil changes. And fuel filter is changed every other oil change. Deleted with stock power tune. Love it

That pretty much explains it. I dont normally drain oil. I change the toilet paper filter and add a lot of make up oil. I am keeping the oil as clean as possible and diluting the soot too small to be filtered out. If I cant stay ahead of the submicronic soot I will drain the oil. Its easy on the Pontiac. I cant see the soot on the dipstick. I can see it if I put it in a gallon wine jug. I normally change the toilet paper and add a quart of oil every 6.000 miles on the Pontiac. A lot more often on the Ford diesel tractor. Some bypass filter makers mislead by showing the oil before it naturally gets black.

Cool video, great explanation 👍

Could you do two oil changes with an el cheapo oil (in specifications ofc), run the engine and then after the two changes put the good quality oil inside? I am speaking about doing this procedure once you buy a used diesel or about every 5 years or so. Would it be much less soot remaining inside the engine?

I have a 1987 cat d3b which is a non turbo. The oil in this dozer has never once turned black. It will stay pure golden up to around 500 hours. There's currently about 600 hours on the oil and it's still has a brown transparent look to it. It has a fair amount of blow by from the down tube and doesn't hardly burn any oil. I just can't explain it, everything else I own new or old gets black instantly.

Good video. Just purchased a 2012 dodge....the oil is black. Changed it again....still black. Changed it a third time. And its still black. Will seafoam help this motor out. What can I do to flush the carbon out. The motor is stock. Not deleted. 82000 miles on the motor. Used as a hot shot truck. Thanks.

My oil is still clean and golden after 10,000 kms of use. 100 series land cruiser 4.2lt diesel turbo

I always thought it was the very high compression that diesel engines run with that causes that blowby as GDI is directly injected into the cylinder on gasoline engines and their engine oil remain clean for at leash 2500km

Excellent video!

If you add a extra bypass filter, can't this help??? Also, if you have a pre-emissions engine (pre DEF) does it still dothesame thing??? Great topic, great video!!!

I'm a veteran and would like to say well done on your vids, my friend... Have you done a clip on slow diesel performance, especially at roundabouts and junction stops, plus why putting petrol to your diesel will rectify, miraculously, your poor performance, as there is a good reason/// Many people, who have put petrol in their diesel, may have found this fact out/// I did, when I was a rookie, and wondered why this happened// I know now, why it happened, but tell the guys why this miracle happened... Best of luck from England...

Thank You for the info!

i have a 1984 6.9 idi f250 im having trouble with a hot start truck runs good cranks right up in the mornings but wont start when it gets hot can you help thanks

I've been told that it is better to keep my Diesel engine running than turn off when running in pay for fuel, or a short stop. If we stop to eat lunch in coach is it better to leave it running or turnoff? Thank you in advance for your information.

Diesel particulate filter? Oh yeah, that's the thing up in the garage loft, along with the EGR valve and stock air box. Flashed the computer and added 40 horse. Sampled the last change and Blackstone Labs says all is good. Oil stays a nice dark honey color the first couple of thousand miles. The engine seems very happy without all that stuff.

At the place I work we have a dump truck with a C7 cat motor. Even when its sitting in the 55 degree shop it takes a good 5 or 6 seconds of cranking before the engine actually starts. Seems like alot of cranking to me. Could this be because the the motor has a HEUI system and it takes that long to build enough oil pressure?

I've had a number of diesel cars and light trucks as well as small diesel tractors and yea the oil went black fast, I even had a MB with an added Frantz toilet paper filter and that was no better. The exception to all this was my Ford Excursion with the 7.3 L turbodiesel, the oil in that was always cleaner than in my gas engine cars and would be cleaner at 9000 miles than my MB was on the day after a change. The Ford had a big crankcase and a BIG filter but even so, the MBs had fairly big filters too and they were black. My mechanic also had the Ford and his oil was clean too and he did a lot of heavy towing with his. Ok, can you explain this or know somebody who can. My go to oil is Shell Toris 15/40, good stuff.

is it good to use engine flush before oil change???

I have a 200 d lincoln welder with a Kubota motor. I change the oil every 100 hours which equates to 6000 mile and it old gets dirty the last 10 hours or so. I have always taken very good care of it. Bought it new. Just throwing it out.

5:36 Having used activated charcoal (which is carbon) to brush my teeth a couple times and having a shirt still stained with it, I can confirm this.

diesel pistons look huge compared to gas ones. is there a practical reason for this?

Thanks man. I will stop worrying now coz i changed my after 6k km. Was very black 😢

Very well explained!

nice video, thanks for sharing.

That's why I got an Amsoil bypass oil filter system for my 7.3.

love the videos learn something new all the time. I have a question for you, when I idle 3406e cat I get oil seepage out the exhaust I don't idle often but when I do I'll set the throttle up to 900 to 1000 rpm and overnight I'll have a puddle. The guys at Michigan Cat told me to add oil stabilizer?

Thank you! very good and simple

Thanks man, I changed oil on gasoline and diesel car at the same time and after few weeks I just randomly decided to check, the gasoline engine oil was still clear but the diesel was black.. I wasnt worried cause they teached me thats its okay but I wanted to know why..

All my Diesel engines are spotless. I have spent a lot of time cleaning them out inside and out and change the oil and filters often. My oil comes out nice and clean, still Carmel colour. I'm very happy with it as my engines run superb. A clean engine is a happy engine.