[OT] Engine braking

[Walter Bright]

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 :-)