Depends on your driving.

10,000km's is my bench mark for changing oil. Used to work out to every 4 months, now with different driving it's every 6 months so I might back that interval down a little.

 

I change my every 6k to 7k but I drive crazy hills and a 100+ miles a day and I Hall lots of tools I use Rotella T6 you can use Amsoil oil but pricey change it every 15k but Diesel oils are all about Viscosity The amount soot changes the Viscosity

 

you can do a Engine Oil Analysis to determine oil change interval.. The black stuff may give you the heaves, but doesn't seem to hurt anything. Mine will go over 10,000 mile with a good EOA report on dino oil.
Do not use my results as your reference. Establish your own results, for the way you drive. And the oil you use.......

 

I did an oil change in my Kubota this summer after 100 hours of moving lawns, left the oil in a jar on the bench to settle so i coupd see how much black stuff was in the oil. In 3 months it did not separate a bit. I've heard of guys dumping used engine oil in the tank, no way that is going in mine. Also I think the 100 hour oil change interval is too long, yet Kubota has small engines rated as much as 400 hours between oil changes

I guess I'm stuck with "oil's cheap, engines ain't" so I will change more frequently

 

Good motor oil with lots of detergent to keep the soot in suspension, the black stuff will never settle out to the bottom.

Pull a sample via the dip stick tube or by the plug on top of the oil filter housing at and send it in. Request a TBN along with the basic oil analysis test. TBN is basically the indication of how much from original the oil still has of oxidation prevention additives. Prevents acid buildup. When it drops below TBN 2, change the oil.
With stock fueling, good none leaking nozzles, little cold short distant driving, no lugging, some towing, clean turbo, no cyl. carbon and a good functional open crankcase ventilation system, bet you'll go over 10,000 miles before the TBN drops low.

Cummins 5.9 is one of the easiest diesels there are on oil. Not so one of the active EGR engines like the 6.7 or the 6.0L Ferd farm cornbinder motor.
This modern crude oil base 15w40 major name brand CJ-4 is an outstanding long life motor. Much of it is thrown away with half or more of it's life left.
Want long Cummins engine life? No lugging, good injectors, no grocery getter short cold driving.

Leave that oil in. Black is good

Blackstone Labs for diesel oil and transmission fluid/lube testing.

 

I Like low rpm low load driving, tuner on performance. I noticed without the tuner the oil stayed clean a lot longer

 

I change my oil once a year and send in oil samples twice during that year. I average about 15K a year driving. Most of that is HWY and some back road. My TBN after that many miles stays around 8. I also change my oil filters once during that year interval filling each with new oil when I do the install. My rig has 119K on it and uses no oil between changes.
Some like Dino and change their oil every 3 to 6K which IMO is overkill. If you dont use Oil Analysis you are not getting the full picture of what your engine is doing. Oil Analysis will also tell you not only if your oil is still good but will catch leaking head gaskets. bad injectors or excessive engine wear that you wont know about otherwise.

 

Unless you are considering long oil change intervals, change according to the manufacturers severe service schedule (1 year or 7500 miles) with a brand name 15w40 and don't worry about it.

A $25 oil analysis every year (no need to pay extra for TBN with the above interval) is probably worth while to identify any issues.

 

The main filter is 20 micron, I added a 2 micron oil bypass filter which filters 10% of the oil while the other 90% goes through the main filter. After an hour of drive time, all of the oil has gone through the 2 micron filter. This will trap almost all heavy metals and larger soot particles, but the oil is still black as black. Its just the way diesel oil is. I run synthetic, so every year or 25K miles, I send in an oil sample for analysis. In return you get a beak down of all elements that are in your oil in ppm. They tell you whether to change the oil, or just change filters. I have only changed filters.

 

I like the bypass filter idea. Sounds like a god idea to remove smaller particles

 

Oil analysis will catch dust leaking air filter, air box, intake tube or seals. Shows up as rise in silicon common element in dirt. Eats the compressor wheel until its worthless and takes out the engine.

Intake dust leaks are the 2nd highest killer of these diesels after worn leaker injector nozzles. Some guys will hand onto those high priced weak baby diaper aftermarket air filter elements until you can see the St of Texas thru them, too cheap to spend the ripoff price of a new replacement.

 

Change mine every 5-6k.

 

Im running regular rotella 15-40. Started at 5k oil change intervals and been getting the oil tested at blackstone. Everything came back good at 8k and now going to try 10k. If you can double you oil change interval, I think its worth the investment of getting you oil tested so you get a baseline. It also picks up any weird readings. Cant hurt to get a picture of whats going on inside you engine.

 

oil should be changed yearly even if a garage queen

 

I agree with dirty silver bullet. I run valvoline 15 40 and I used to change it every 5000 km. Started mailing my samples to black Stone and bumped it up to 8000 km. Test just came back good so now I will try 10000 km and send it out again. Just the longer intervals has saved me a bunch of money and given me peace of mind that my engine is still strong.

 

I usually change my oil around 15-20K miles intervals because I get bored. I do oil analysis at 5 to 8K mile intervals or so, usually changing the spin on filter at that time. One thing I notice that is missing when people talk about oil analysis and extended drain intervals is Particle Count. Particle Count by Pore Blockage is an excellent tool to see the true effectiveness of some "by-pass" filters. There are quite a few claims, but little documentation to support their performance.