Questions on oil

I can't see doing extended drains without a bypass filter system. Keeps the oil nice and clean and you can by filters now that have the base oil chemicals built in when you need it. Start on a good oil analysis program along with it.

 

Are you running on regular oil or synthetic?

 

while modern motors are far cleaner on the oil than motors of yore.....i believe these extended drains are driven more of environmental reasons.

although,an oil analysis doesn't lie.

 

I ran normal oil in that motor. This new one I'm using synthetic. But DD15 do not get an extended change interval for using synthetic.

I did have oil analysis done from the 400-500k mark on. At 750k it showed some coolent in the oil. Took it in they changed some gasket and she was clean to the day I traded her in for this at 1.2 million miles. I switch from 50k to 35k at a mil not due to something changing in my analysis but for peace of mind.

 

You really can't compare ISX motors to DD15s. Everyone knows you can't get a million miles with an ISX trouble free.

 

I have tended to use used oil sample analysis to my advantage. I watch the trend lines. I get gradual, consistent wear metals, TBN depletion, etc on a study curve till I hit around 22,500 miles, then I start to get spikes in various numbers. That was true with an N-14, a ISX, and my current Series 60. While the oil is still technically good, I settle on 22,500 as my limit because of those spikes. It is apparent that something the engine and oil doesn't like about going beyond that to cause spikes outside of the normal trend line. Each engine is going to be different to some degree. In that 22,500 miles, I use between 2-3 qt of oil. But it is a factory reman Series 60 with 540,000 miles on the reman. Oh, and I am using a 10w30 syn blend in it. As good or better UOA's than with any 15w40 I had used previously.

 

Im going to caution you on 15K oil changes. DOT uses this metric to detect logbook abuse for those running paper logs and do not have a team aboard.

I used to run really hard and kept legal logs only to discover when I attempt a second oil change at 15K miles in a month it's a yuge red flag. So. I just skip it and postpone it. The engine is so well taken care of anyhow a few thousand miles won't hurt none. Especially with a pampered kitty.

 

How long since the overhead / valve set has been done?
I used to have a Mercedes in a Century. When I bought it I was told that if I notice the oil consumption increase, then it was time to run the overhead. I had it done initially at the recommended interval, then after a few years I forgot about it. When I noticed it was using more oil I started to get concerned, then after some time I remembered what I was told early on. So I had the valves adjusted, and presto, oil consumption went back down to normal.
I don't know if it applies to the DD15, but it may be worth a shot. They do have awfully long intervals for recommended valve sets.