Synthetics get contaminated just like dino oil
and the acidic by-products of the combustion
process will make me change mine every 6 months
even though I rarely see 1500 miles of use in that time.
Its not the construction of the oil but what gets
added to it when it sees service.
Mine always looks good as new when changed but
a simple oil analysis would show the contrary...
After the 1500 in the Stang, the Chally sees the rest
of the oils life. Double duty of sorts.
If there is no molecular breakdown, a simple filtering
will return used oil back to life.