Is the recommended break-in period for a new car really important?

Dear Car Talk

Dear Car Talk | Sep 01, 1997

Dear Tom and Ray:

Is the "recommended" break-in period for a new car really
important? My new Corolla's manual says that for 1,000 miles I
can't drive faster than 55 mph, can't drive at steady speeds,
etc. It's a bit frustrating to get a new car and be told right
off the bat that I can't fully enjoy it for 1,000 miles. What
bad things will happen if I ignore these recommendations? --

TOM: Well, you may develop chafing and itching around your lower
extremities, Michael. And if it continues after the first 1,000
miles, you should definitely consult your doctor.

RAY: Actually, we can't say for certain what will happen to YOUR
car if you don't break it in properly, but I can tell you the
widely accepted theory. The piston rings don't fit the
cylinders absolutely perfectly when the car comes off the
assembly line. Why? Because the spaces in between the two are
tens of thousanths of an inch. So the break-in period is
supposed to be a time in which you drive gently and allow the
rings to "seat," or mold themselves perfectly to the exact
shapes of the cylinder walls.

TOM: If the rings don't "seat" well during break-in, the theory
is that your car will burn oil later on, because the poorly
seated rings will eventually let oil sneak by and get into the
cylinders. Is it true? Yeah, probably. Although it's less true
than it used to be.

RAY: Manufacturing technology has improved so much over the
years that the rings (and all the other engine parts) come off
the assembly line fitting pretty darned well. And overdrive
transmissions further reduce the risk by allowing engines to
turn slowly at highway speeds. So where, in the old days, a good
break-in might have made the difference between your engine
lasting 35,000 or 70,000 miles, now it might make the
difference between your engine lasting 100,000 and 200,000

TOM: So it's up to you, Mikey. You can have a good time for the
first 1,000 miles and take your chances. Or you can show a
nose-hair's worth of restraint and have a good time for the next
199,000. Your call.

* * *

What's one secret of financial success? Driving a used car! Read
How to Buy a Used Car: Things Detroit and Tokyo Don't Want You
to Know. You can order it by sending $3 and a stamped (55
cents), self-addressed, No.10 envelope to Used Car, PO Box 6420,
Riverton, NJ 08077-6420.

Get the Car Talk Newsletter