Date: Thu, 15 Apr 2010 11:48:05 -0500
Reply-To: Tom Hargrave <thargrav@HIWAAY.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Hargrave <thargrav@HIWAAY.NET>
Subject: Re: Now Preventative Maintenance, Was Do U carry spare ECU?
In-Reply-To: <t2s86476e251004150827lbddcad31peed6484eb8006afb@mail.gmail.com>
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The study is absolutely correct. But my "generic" PM list includes service items and vehicle specific items with known failure rates. For example, the vacuum pump on a late 80's Mercedes diesel engine is known to disintegrate somewhere after 160,000 miles, taking the IP timer & sometimes the rest of the engine with it. The problem is a roller bearing fails suddenly and you know only when it's too late, sending hard metal parts into the engine. So I replaced it at 150K miles even though the one I took off "looked fine".
I would think the same logic would apply to the vanagon ECU? But instead of replacing you would take a peek to see how far the carbon was worn? Then repair if necessary?
Would you wait until your oil failed before replacing it? Or would you wait until all of the corrosion inhibitors were used up in your coolant before replacing it?
I wouldn't but this seems to be how we maintain vehicles in this country.
Tom
www.kegkits.com
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of Loren Busch
Sent: Thursday, April 15, 2010 10:28 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Now Preventative Maintenance, Was Do U carry spare ECU?
On Thu, Apr 15, 2010 at 7:47 AM, mark drillock <mdrillock@cox.net> wrote:
> It is a fine theory to say replace things in advance of their failure
> but experience shows that the replacement parts are often what fails
> these days. Whether that is due to declining parts quality or lack of
> workmanship in the replacing, I'd say some of both.
>
Mark has a good point here. In the 1950's the US Navy did a study on the value of 'preventative maintenance' on electrical and electronic devices.
This was back before printed circuits and solid state electronics. Most control and switching circuits were relays and many of the relays were open, not encased, like in cross bar switches. And regs at the time called for periodic cleaning of the relay contacts. They found that their down time and failure rate dropped dramatically when they quit doing the cleaning, only cleaned (reads 'messed with') things when there was a failure or malfunction. The process of doing the preventive maintenance was causing more problems than it was preventing. Later studies confirmed this for other electrical and electronic devices. They also arrived at the conclusion that 80% or better of failures in electronics (especially after the introduction of solid state devices) was mechanical in nature, bad connectors, corroded connectors, broken pins, poor contact, etc.
Now, how many times on this list have we read about problems arising right after work has been done or parts replaced? And how often have various problems been diagnosed as loose connections, corroded wires and plugs and connectors, corroded gronds, etc? The mechanical part of the equation.
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