With the odometer showing the miles hold the trip meter button in for 5 seconds or so. You should see engine hours come up in the odometer window. This is the total engine run time as tracked by the ECU. Divide your mileage by the hours and you have an averag mph number.

That is one important number is what you should be using to gauge oil changes. Generally if you can keep that over 45 mph average you can extend the intervals if everything else is good. At 35-40 mph is definitely schedule B territory. Between 40 and 45 is no-mans land that you just have to judge how everything else your doing with the truck is working and how you drive it. When you drop under 35 its highly recommended, by Cummins that is, to go to a severe duty schedule and change oil more frequently. I believe the number they throw out is 3500 miles but it is subjective as other variables will influence the decision.

 

I drive about 17k miles a year, largely on paved country roads at 40 to 50 miles per hour. The truck is not loaded to capacity, rarely pulls a trailer. Is virtually always run till fully warmed up. Most trips are at least 20 miles one way. Very little in the way of idling. Because of the slow country roads my average speed is only 32.5mph. Please explain how the low average speed makes my truck fall under severe duty. Oh, I do by the way, change oil at 7.5k because it makes me feel better. I don't do it for any logical reason. Just peace of mind. I am also the type of guy who reads Bob is the oil guy. I read it with the knowledge that like any forum people, state opinions as fact.

 

Extended low rpm operation that does not get the enine coolant and EGT's up to temp frequently enough and long enough. Remember, anything under 1500 is considered an idle situation and tracked as such in the ECU. There is a counter that gives percentage of run time under 1600 rpms and that is the first thing the engineers go for when there is a problem.

The highest BSFC on the CR is 1900-2000 rpms and thats where the engine is designed to run for extended periods. Due to all the emissions controls dropping under 1800 rpms requires manipulation of the timing and fueling that is deterimental to engine health.

 

This post makes very good sense. Can you point me to the literature that holds this info as well as the Schedule "C" maintenance?

I have been changing my oil at 7500 miles for the last 149K miles except for one interval I stretched it to 10K.

To the OP, I have used about a quart between oil changes ever since new. It doesn't matter if I am using dino oil or synthetic summer or winter.....

 

Jesus, you all get worked up over nothing.