Brian - when an engine is new, the cylinder walls and rings haven't "seated"
themselves, so almost all engines should be operated at varying speeds so as
not to "glaze" those surfaces. If they get glazed, oil consumption will be
higher, so the theory goes.
For the typical new car buyer in the USA, it doesn't matter much since they
will probably get rid of the car in 3 years or less. But for people who are
looking for maximum engine life, a proper break-in is a good idea, at least
for the first several hundred miles or so. Once broken in properly, I don't
know of any evidence to suggest that there's any advantage to vary engine
speeds. For example, ship, train, and tractor engines, after initial
break-in, usually run at constant speeds for hours at a time.
And you are correct, higher speeds increase wear - that's another reason
Diesel engines typically last longer than gassers (besides being built to
withstand higher stresses and loading).
Werner
'90 300D 228k
'83 SD 223k
----- Original Message -----
From: "Zoltan Finks" <[EMAIL PROTECTED]>
To: <mercedes@okiebenz.com>
Sent: Friday, January 26, 2007 11:06 PM
Subject: [MBZ] RPM consistency and longevity of engine
The question I have thought about for some time is this: When someone puts
a
lot of highway miles on a car, their engine spends many hours at
approximately the same RPM. Could this cause any inordinate wear (as
opposed
to varying engine speed more, gradually and smoothly of course)? I know
that
when a newly-rebuilt engine is being broken in, they tell you to vary your
RPMs and not to cruise at the same speed on the highway for an extended
period. Any correleation? An benefit from driving at varying speeds over
the
days of your weekly commute for example? (Not that I'd have the dedication
to do it).
I read that article on million-mile cars and one of the interviewees
mentioned that he likes to keep his speed down on the freeway. He had read
something about freight train research that revealed something like 80% of
engine wear ocurred in the top 20% of the engine's RPM range. This is what
reminded me of the question that I occasionally think about.
Brian
83 240D
84 Saab 900
00 Honda CRV
68 Dodge Coronet 500
