On Tue, 30 Jul 2013 15:40:52 -0700, Walter Bright
<newshou...@digitalmars.com> wrote:
On 7/30/2013 12:06 PM, Adam Wilson wrote:
My dad has been an ASE Master Technician for my entire life and teaches
Emissions Certification classes for our state. What I am about to say
is based
stuff I've picked up from him.
I would go one step further and point out that in modern vehicles,
those made
after the EPA catalytic converter and air quality mandates of the early
80's,
that any oil in the combustion chamber is a Very Bad Thing. Unburned
hydrocarbons are highly destructive to catalytic converters and oil
never burns
completely during combustion. In fact we rebuilt the engine on my 1996
Honda
Accord in 2010 precisely because it was starting to burn oil. And
indeed, a year
later the catalytic converter failed anyway due to the excessive strain
placed
on it by the partially burned oil that was forced through it prior to
the rebuild.
My dad actually recommended engine braking (the correct term is
"compression
braking" btw, Thanks Dad!) as a way to reduce wear on the brakes. The
google
poster is correct in this statement that all you're doing is putting
strain on
parts that aren't used that way much, unless you reverse a lot. We see
cars
ranging from the early 80's on up, including carbureted, and we've
NEVER once
seen a car with a transmission or engine that died because of
compression
braking. Given our sample size of somewhere over 10,000 ... :-)
How would you know if excessive wear was caused by engine braking or
not? Excessive wear can be caused by all kinds of things, like not
letting the engine warm up before driving it hard, or running long
between oil changes, shifting prematurely or too late, etc.
Personally, I wouldn't. :-) But my Dad studied metallurgy as a minor at UW
and let's just say that he enjoys Metal Failure Analysis WAY more than one
could charitably consider normal for a human.
Aviation Sidebar: His favorite metallurgy class was taught by an active
duty Boeing incident response team member and his favorite story was his
teacher dragging the failed main gear bogey of a 727 into the room and
asking the class to figure out what went wrong.
If my dad says he has never seen that type of problem, he probably hasn't.
Based on watching do failure analysis' on cars, my guess is that there
would be telltales that clue him into what was happening. As far as the
combustion chamber goes, when we rebuilt my 96 Accord it had some minor
pitting from the repeated explosions but nothing else of note at at 225k.
We resurfaced the barrels and moved on. And I'm a commensurate compression
braker. :-)
Indeed, the other things you listed are quite evil on the internals of the
engine. Particularly going too long between oil changes. But compression
braking isn't on the list from an engineering standpoint. The components
of the transmission and engine and much beefier than they strictly need to
be. No manufacturer wants THAT recall at 5k per repair. Essentially, it's
not any different than driving forward, you are just reversing the stress
on components that were engineered to handle it moving forward. And in the
case of automatics, the Torque Converter acts as a buffer between the
engine and transmission at cruising speeds (varying by model) until it
hits the lock-up.
The automotive industry has spent obscene amounts of money getting the
absolute
cleanest burn they can to meet CAFE standards, and the very first thing
they did
was get the oil out of the combustion chamber. I'll also say that based
on my
dad's experience's with the Emissions class that even competent techs
are having
a VERY difficult time understanding this stuff, the chemistry involved
is Ph.D
stuff, and now ignition system are getting they way too. My dad has
often
lamented that working on cars is now more about understanding the
computer
control systems than it is the mechanics of it. Your average dealer tech
probably has no clue what they are talking about since they have no
reason to
invest in learning this stuff. They don't see the car again after the
warranty
runs out and these systems rarely fail in five years. At least that's
been my
dad's experience with them.
I'll have to add that my knowledge of these things is pre-1990. So are
the cars I work on :-)
Hehe, Emissions Control only really got complicated in the last 15 years
or so. And most people drive cars newer than 15 years, unlike the Crazy
Leader of D Who Shall Remain Nameless. ;-)
--
Adam Wilson
IRC: LightBender
Project Coordinator
The Horizon Project
http://www.thehorizonproject.org/
