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.
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 :-)
