What is the optimal oil change interval?

[bb37]

Really, I didn't realize there were labs that would test this?

Myself, along with several others here, use Blackstone, but there are other labs. Find one you like and stick with them.

Here's a report on my Expedition at 3700 miles:

 

[Avian]

Our dealer uses the "severe" service schedule combined with full synthetic oil on diesels and gasoline, all engines. This corresponds to 50% oil life remaining on the oil life monitor (8000km or 5000mi). I've been following this severe schedule and never had any engine / turbo problems as such. I follow the severe schedule on any brand car.
Unless you drive a lot of highway, severe is the way to go for my area anyway.

And, the real litmus test is to go 250,000 miles, and the manufacturers are keenly aware that VERY few folks make that many miles before they get bored and trade up for new toy "OOH!" factor goodies.

 

[DieselMonk]

And, the real litmus test is to go 250,000 miles, and the manufacturers are keenly aware that VERY few folks make that many miles before they get bored and trade up for new toy "OOH!" factor goodies.

Around here, finding something low mileage for a good price is getting hard to find. There used to be plenty good deals before the pandemic days. Now it’s just robbery, unless you know the dealership well.