[Vwdiesel] glow plug resistance

William A. Thompson twogreek at hotmail.com
Fri May 4 18:11:28 EDT 2007

Be careful about powering a glow plug on the
bench. They get red hot very,very fast and could
sorta' explode because there is no engine to sink
the heat to.

For various reasons resistance measurements, don't
seem to me, to be much of an indicator of a plugs
condition other than a basic "go .... no-go" test.
Even then interpretation of the actual resistance
can be misleading. Amp readings are near foolproof
... but for the possibility of sparks flying.
(VBG as I am guilty.)

I use a common 60 amp +/- ammeter just like one
you would buy to mount on the dash. Since I have a
few Rabbits I don't permanently mount the meter.
Make sure that you use big honkin' cables too
'cause you could be drawing in excess of 60 amps
at times.

I have used the meter on the bench but I prefer to
test them while installed in order to have the
engine for a heat sink. It helps to test the
plug(s) in the new condition so you have something
to compare to as time goes by. The total amps (and
the resistance to some degree) will change with
time even though the plugs are working fine. I
haven't tried this but it might be of benefit for
someone who lives in the extreme cold to keep a
running record of the diminishing amps (with a
better meter) to get an idea of when it might be
prudent to think about replacing them.

Put in new glows, put the meter in series with the
buss and the glow plugs (either side of the fuse)
in order to get a reading when they are all new.
Later if you think you have lost one glow the
total reading should be near 3/4 of the original
total reading, 2 glows 1/2, etc.

You do have to test each glow individually to
isolate which is bad. Disconnect the buss at the
glow plug and hook up the meter in series. Each
glow should read about 1/4 of the total amps.

    ... Bill

----- Original Message ----- 
From: "raymond greeley" <rgreeley2 at hotmail.com>
To: "James Hansen" <jhsg at sasktel.net>;
"Vwdiesel at vwfans.com" <vwdiesel at vwfans.com>
Sent: Friday, May 04, 2007 7:11 AM
Subject: Re: [Vwdiesel] glow plug resistance

I understand just replacing old  with new, the
labor is the killer, I did that
very thing with the daily driver. While changing
them out i also eleminated the buss bar so i could
seperate each glow plug circut in future
diagnostics. certainly i can apply 12 volts to
those out of the engine
how is it that i test the individual glow plugs
while in the car.
 I remember reading here that we measure
resistance though i don't
see a consistant measure when i do this. maybe my
gauge is not woriking
correctly or the connection is suspect.
> Date: Thu, 3 May 2007 22:45:56 -0600> From:
jhsg at sasktel.net> Subject: Re: [Vwdiesel] glow
plug resistance> To: rgreeley2 at hotmail.com> > give
them 12v with a spare car battery or use jumper
wires from your car > battery. They get red. THe
ones that don't are not good.> If you have the
motor out, just install new ones behind the
injection > pump. Yeah, I know, it seems silly
when you have a handfull of them, > but you'll
understand when you're wrenching out the used one
in a month...> -j> > raymond greeley wrote:> >
Hello All, Needing some info on checking the
condition/resistance of glow plugs. several are
out of the> > engine and I have an engine out of
the car on a bench that> > i would also like to
test the glow plugs on along with testing several
other items before i install the engine. what kind
of > > ohms am i looking for as the archives are
unclear or is there> > another measure i should be
testing for. thanks, ray> >
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