Diesel RVs: Re: [diesel_mercedes] the falacy of replacing glow plugs "just because".

Bogy,

While I understand what you're saying, with glow plugs, I usually just
replace the bad ones, yet I don't remove them to test. If I did remove
all the glow plugs, I'd replace them all, though save the old "good
ones" for backup. I've noticed that if I change 1-3-5 this time, 2-4 are
the next to go out, and later 1-3-5, etc. I always get Bosch, and keep
extras in the truck, so if I'm traveling, it's a quick fix (except for #5).

Rob
'85 300D
Garden Grove, CA
==

On 2/14/13 9:57 AM, diesel_mercedes@yahoogroups.com wrote:
> Guys et. al:
>
> I would like to address the comment included from an earlier email in this thread. I quote it here for reference.
>
>> > but I cannot imagine putting any of the old ones back in, and
>> > having to go through that again!!
> And with all due respect to dissenting opinions I would like to tell you, as an electrical engineer, why I do not replace glow plugs, or any electrical part for that matter, just because I can.
>
> While it is true that mechanical parts begin to wear out from the moment they are installed and as such virtually any new mechanical part is superior to a used one, the same is not true with electrical parts. It is literally a case of what doesn't kill you makes you stronger. Or more accurately it is a case of "what doesn't destroy you soon will probably not destroy you later and so proves how strong you are".
>
> Perhaps the best way to describe my logic is to use the reality of the difference between military grade Integrated Circuits or ICs and civilian or common ICs. As you might expect, military grade chips are those which withstand more stringent extremes - higher voltage extremes, higher thermal extremes, higher vibrational extremes, and the list goes on. Virtually every characteristic of a chip is held to a higher or more extreme standard for military grade parts.
>
> But the military doesn't get special grade parts made just for them from special factories made from special source materials. Military grade parts come out of the same batch process that civilian parts come out of. So what is the difference? Simply put, they beat the hell out of the civilian parts and those that survive become military grade parts.
>
> And do you know why that select group of parts cost so much more? It's not the testing. The testing is simply a matter of turning up the requirements on the testing machinery (that every part goes through anyway), and putting the parts under the increased stress. So while each part is always tested, the military parts are just held to a higher standard. No, the reason they cost so much more is because of all the civilian quality chips that have to be destroyed to find the few that will pass military standards. The cost of the chips that they cannot now sell because they had to be destroyed to find the few, the best, the military grade parts, are folded into the cost of the military parts. In other words the military pays for the chips that go into the weeding out process, NOT just the ones that make it through. And the chips for the civilian market include ones that would have passed military testing if they had been subjected to it. We just don't know
> which ones they are. And the only way to find them are to put them into service and see which ones fail first.
>
> So what does this have to do with glow plugs and other electrical parts. Simple. Once a part is put into your car, or any other service, it begins a stress test of its own. Some parts fall out sooner than others. The ones that survive the longest are the ones that will probably last forever. The longer they last, the longer they are likely to last. Just the opposite of mechanical parts.
>
> I haven't replaced a plug in my 81 300TD in over two years now. I have had it for nearly 10. I have put 80 thousand miles on it in that time. And I have replaced some plugs over the years. But why in the world would I replace a plug that has proven itself in service with one that hasn't? Just because it is "brand new"? Screw that. I know too much about electrical parts to deliberately sabotage my life that way.
>
> I don't like replacing glow plugs any more than any one else does. That is why I only replace the ones that go bad. And that is becoming an exponentially decreasing activity as time goes on. Because they don't wear out over time like mechanical parts do. They prove themselves.
>
> And eventually my engine will be populated only with glow plugs that are the cream of the crop, having proved themselves by surviving the stress tests of actual usage. They are the ones that would have passed more stringent tests to begin with had they been subject to them.
>
> But any one here who wants to get rid of their working but replaced glow plugs, I will gladly take them off your hands. In my book they are worth a lot more than unproven new ones.
>
> Bogy.