Change Up

How often should I be changing my oil?
The car is a ’72 Challenger, 340, with
some mild bolt-ons. The engine is original
with 72K.

There are several factors affecting oil
change intervals. If you make lots of cold
starts and the engine rarely full warms
up, so that it is running choked much
of the time, or if you are silly enough
to be running on the street with a
double-pumper carb, or with no vacuum
advance, you might need to change it as
often as 1,000 miles. On the other hand,
if the tune is razor sharp, you drive at
least 15-20 miles each trip, and hammer
it at least a bit on each trip, you could be
safe at 4,000, especially if you use full
synthetic.
For most of us, the recommended
number is somewhere in between these
distances. The factory also threw time
into the calculations, figuring that if you
only drove, say, 2,000 miles in 90 days, a
reasonable conclusion was that you had
driven mostly short trips, so you needed
frequent oil changes—every 90 days.