Post by
EdBwoy »
https://forums.nicoclub.com/edbwoy-u213758.html
Sat Dec 09, 2017 1:54 am
What kinds of OCIs are you used to? 3,750 miles doesn't seem that bad to me... but that is Schedule 1, for cars operated in severe conditions. Schedule 2 is 7,500 miles.
These days I use synthetic and aim for 5,000 miles.
{Recall that my numbers are just for illustration purposes}
I have never designed a car engine, but I used to work as a reliability engineer and among other duties, we would make these very decisions and write the maintenance manuals for our equipment. The manufacturer would recommend an interval, but sometimes we would tweak these to suit our production schedules. So, this is how I would do it if I was writing the manual for Nissan:
A.
Start with brand new engines running in a test facility or in a pre-production car. You monitor oil life at various durations, like how many revolutions/hours the engine has ran.
There are industry standards on what points oil loses its ideal lubrication/cleaning/cooling capabilities. In the lab, used oil samples are collected and analyzed every midday. They note down when each engine started to exhibit oil deterioration below the acceptable standard.
B.
At this point, I'd look at the history of each engine and convert the days -> hours -> minutes -> engine cycles/ revolutions.
Then I make some assumptions on what a hard driven car will do in speeds and convert those engine revolutions to miles because in the real world people monitor miles (or hours) of usage rather than cycles.
C.
Unless there is a crazy outlier that was breaking oil down at 1,000 miles while every other engine was concentrated around 4,000 miles, then I go to the bell curve of data points and choose the lowest point. Assume most engines are in the 3,700 - 5,000 range while your highest sample went for 7,000 miles.
Ignore the top range when writing a manual.
No point in sticking my neck out and being liable for the fraction of cars that damage their engines by following my middle-ground 4,500 mile OCI. I'd just give you the lowest reasonable number so 99% of the engines are covered.
And that is how I would come up with the Schedule 1 maintenance schedule.
Repeat the experiment with the engines running at moderate load to come up with the Schedule 2 recommendation.
*Now, if I wanted a smarter schedule to account for grandma and a lead-foot teenage kid and their presumably different driving habits, I'd make my maintenance logic tied to individual car behavior and the data the ECU is collecting anyway. I'd set up an algorithm that still targets number of engine cycles in the end; but gives allowance to things like ambient temperature, engine temperature, engine and car speeds, throttle position, etc... so that in the end even if grandma and grandkid got an oil change on the same day, grandma's oil life monitor would still show 30% when the drag-racing teenager's is showing 5%.