[Vwdiesel] Slowing death of Glowplugs

Thu Dec 30 22:58:51 EST 2004

There is afterglow period on VW diesels, determined by the temp input.
Colder engine temps get longer afterglow.  The dash light (led) is no
indication of glow plug power... or not.  It's simply run by a timer to tell
you when to start the car.  Having had a bus bar indicator light on diesels
A1 through A3, I can confirm that they all just work mostly the same.
Light comes on, goes off to inform you to hit the starter, then glows for
around thirty seconds after starting when it's cold. If you don't hit the
starter, it also goes off after thirty or so seconds so you don't kill
either the plugs or the battery because someone who doesn't know enough has
the key on to play the stereo.

Less power to the glow plugs would be good if maximum glow plug life was the
design goal.  Since maximum starting is the goal, don't frig with it, it
works just fine.  A light for each plug is sort of spinning the wheels a tad
too.  It's pretty nose on your face type of diagnosis that one plug has
died. It's also a ten minute test to determine which one.  I could see
spending some skull sweat to figure something out if it took hours on end to
diagnose, but if it started good yesterday, and it starts like one piston
fell out today, you have a dead plug.

I always change all the plugs at once. If one goes, the rest are soon to
follow, and will do so at the worst and most inconvenient time possible,
like in an emergency when the car HAS to run.  I have a small pile of used
"good" plugs that I can't throw away, but are kept as spares... Funny thing
is whenever I convince myself to use one, it dies.  They are basically like
tips for the mig welder- consumables. Beats the piss out of lighting a twist
of paper and screwing the glow plug carrier back in every time you want to
start the engine like on some of the older stuff however.

I've been reading the thread on testing plugs.  Interesting.
I mentioned on the 28th that there were three ways to test in situ.
Current, voltage drop, and temp gauge.  I've used all three, and they all
work.  Trickiest is the voltage drop across each plug, but you have to have
some knowledge of how to use a meter properly- for millivolts, the bar has
to have impeccable contact with the probe.  clamps are preferred.  Measuring
millivolt drop is like measuring wind velocity across a butterfly's wing.
Clamp on meter is okay, but the small probes are rare and pricey.  I've only
used a borrowed one a couple of times, but function is good.
The laser guided infra-red temp gauge is easiest.  cycle the plugs a few
times with a cool engine, and it's easy to do, just have to get the end
fairly close to the plug to keep the sample area down. It's nice for reading
exhaust manifold temps too, to tell if one cylinder is lazy.  Works pretty
good for tire temps too. I use mine quite a bit. Very versatile and handy
shop tool.

-James

-----Original Message-----
From: vwdiesel-bounces at vwfans.com [mailto:vwdiesel-bounces at vwfans.com]On
Behalf Of Val Christian
Sent: Thursday, December 30, 2004 5:01 PM
To: vwdiesel at vwfans.com
Subject: Re: [Vwdiesel] Slowing death of Glowplugs

I would not really want to reduce the voltage to the glow plugs,
as that will impact starting efficiency.  Since the temperature
vs. time curve on the GP is rather long, it might be better
to heat quickly, for shorter, than slowly for longer times.
Not only for efficiency, but also for GP life (other problems
can include bonding problems, insulation failures, etc.).

As for Hagar's concern about life...the laws which apply to
incandescent lights, also apply to resistive heaters.

Enduring upstate NY winters, I'd rather have 13V sitting on my
glowplugs some cold morning, rather than 10.3 or 10.7 volts.
Think twice about reducing voltage.

As far as I know, glow plugs on A1 and A2 IDI engines are not
run after the starter engages.  That's a function of the glowplug
relay.  The relay gets a signal from the starter, which stops the
glow cycle.  If the GPs come on after the starter signal,
without a power-off of the ignition, then there is a failure
in the relay.  This used to happen often on A1s, for two
common reasons: infant mortality and water-induced failure.

I've never had a glowplug fail the same season, except when
there was an injector or runaway oil ingestion problem.
If your injectors, and the glowplug power system works OK,
then the liklihood that even one plug needs changing in two years
is quite small.  GP failures are signs of other things gone
wrong.

Val

>
> I think this confirms what I said about the vulnerability of
> the plugs. It also makes me want to set up the passive LED
> system and using the blocking diodes in each GP supply would
> reduce the applied voltage and  power output of each plug.
> Being able to turn off the glow plugs as soon as engine
> starts also helps and this is now incorporated into my
> Quantum.
> Mark(The Miser)UK
>
>
> I have had at least one experience where boosting a tired
> diesel in winter
> from a healthy truck with a good alternator resulted in most
> of them going open.
> I suspect the boost (at 13.6v) from the healthy truck, with
> big cables, was
> more than they could take for any length of time.
>
> Sandy
>
>
> Sandy are we dealing with the OLD style plugs ?   if so
> from 11 Volts to 13.6  will
> kill em fast.
> Remember the square LAW ?   double the voltage  gives 4
> times the heat.
>
> I have no tables for heaters  but Lightbulbs   according to
> Westinghouse goes
> as follows.   Increase voltage from 100   to  108   reduces
> life to  50 %.
> Reduce voltage to 92 Volts     life is increased to 310 %.
> Glowplugs are probably similar to Lights.
>
> What kills em ?  ---HEAT.          pure and simple.
>
> Does a glowplug do any good at reduced voltage
>   ---absolutely. Make a step
> down resistor system and have lots of AFTERGLOW.
>
> Will explain how I did it some other time..    By the Way
> the red wire with 4 white
> stripes ?   ----VW   1980 ?  it is bigger than # 12 but
> smaller than # 10   ---so we
> are looking at slightly more than 1 OHM per 1000 feet.
>
> VW wire gauges are mm square. ---- way better system than
> that garbage USA wire gauge shit.
> Mark Shepherd what is the standard in the UK ?.
> In Denmark it is square mm  simple to use.  2.5 ?    house
> wiring. For DC just double for
> double amps.   Try that on a USA system ?-.
> USA is a retarded ---- outmoded  STUPID  system. IMHO.
> Brown and Sharpe wire gauge ?
>
> Bigger number smaller wire ?   go figure.    ---I tried but
> it -- it is still STUPID.
>
> As you go bigger ?    0    and 00   and 000  and so on ?
> Anyone know of somethig
> dummer ?
>
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>

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