Re: its a 1985 300 SD. The temp went down to about 45 overnight, and
in the morning it took a long time to start... when in warm weather it
starts instantly. Just last year I think I replaced 4 of the five
glo-plugs myself, and paid a mechanic to replace the one in the rear.
. So they shouldn't be burned out already!(On this car, the glo-plugs
are wired in parallel, BTW) I put a volt meter on each one....they
all have 12 volts power. My DC amp-clamp is too big to get onto each
glo-plug wire, but I did get it around the bundle just ahead of the
first glo-plug, so I was measuring the total current. It read only .2,
or 200 ma. So the question is, how much current should a glow-plug
draw? Should I be able to feel heat on the tops of the glo-pugs after
a few cycles? The relay appears OK, they stay on for around 1 minute.
I guess tomorrow I will have to read resistance to ground at each
terminal, to confirm if open/bad. Come to think of it, from the
resistance, I should get an idea of about how much current each should
If the glo-plugs are all working, does this mean the compression of
the engine is way down? It is not burning very much oil. Smoke
billows out of tail pipe only for the first few seconds after
starting, then there is very little smoke, and it does'nt appear
bluish. Thanks all.
By measuring the voltage at each GP you have established that the leads are
OK and voltage is getting to the GPs. GP resistance is much less than one
ohm so each will draw over 12 amps, I=E/R. IIRC the main fuse is 80 amps
and whatever you measured is way off. Each GP should measure close to a
short or not quite zero ohms and depending on your ohm meter you should see
approximately 0.5 ohm depending on the accuracy of the meter, resistance of
the test leads and how good a contact you make with the plug. If a plug is
shorted, the meter will read pretty close to what you read when you short
the leads. If its open it'll read very high. Just like new light bulbs
failing prematurely, GPs can too.
"Geronimo" < email@example.com> wrote in message
The reading of "amp draw" in a bundle of wires is not a good practice. Any
current flow "TO" a device on one wire, is "RETURNED" on the other wire. The
net is "ZERO". Separate the wires and you will read current to the device in
question. The value of 200ma is probably from a device that does not have a
return wire in that bundle. Hope that is understandable. Also DC Clamp on
Amp meters have polarity associated with the position of the clamp head. So
the polarity value might change depending on the direction that the meter is
The reading of "amp draw" in a bundle of wires is not a good
current flow "TO" a device on one wire, is "RETURNED" on the other
net is "ZERO".
That is true in the general case. But for glow plugs, as for many
loads in autos, the return path is through the metal of the car itself,
not back through a cable bundle. For glow plugs, the return path is
through the engine block, isn't it? So it would seem to me a clamp on
DC current tester used over the entire bundle of glow plug wires as the
OP stated should read the total draw.
Exactly....the return path is through the block on all plugs, so that
is why I should get a valid reading of amperage by clamping around the
whole bundle before it branches to individual plugs. Didn't think
about this yesterday when checking for power with my hi-impedance
multimeter, but it is possible that the main power wire
or glo plug relay is not completely open, but resistive. I have seen
this before on aircraft electrical systems. Checks good with a hi-Z
DMM, but when you put a test light on it, which gives the wire a load,
the wire cannot supply any appreciable current because of abnormal
resistance, so test light does not illuminate as it should. Will have
to recheck with a test light. The gas is fresh diesel, BTW. The
temperature overnight never got below about 50 deg., yet I had to
crank for a long time before it would start this morning.
Now that I know what amount of amperage I should have, I should be
able to figure it out.
I have the diagrams in the Haynes manual to go by. How in the
world do you make sense out of those German electrical schematics?
US/American is so much easier!
On 26 Oct 2005 05:51:36 -0700, " firstname.lastname@example.org"
I found good power with a test light at all the glo-plugs, so I
read resistance of each. All five plugs are burned out! This despite
replacing the plugs only about a year ago. I have never had voltage
regulator problems where the voltage was going over about 13.5 - 14,
so I don't know why all of them burned out so quickly. They are Bosch
glo-plugs, made in France. Got them at Autozone....I think they cost
9.99 each....when NAPA wants about $25 each! Maybe I would have done
better to buy the $25.00 ea glo-plugs, if they last a lot longer!
Beru also makes an excellent GP.
There's something wrong in the glow plug relay that caused all five GPs
to fail within a year. The relay isn't shutting off the current and the
GPs are glowing and glowing and glowing while you drive.
No GP can survive that. New ones will work for a few days or weeks and
then will need to be replaced.
GPs usually last a long long time. The original GPs in my old '80 300SD
lasted about 100K miles - 22 years!
On Fri, 28 Oct 2005 22:54:55 -0700, "T.G. Lambach"
==========Some people think that when the dash glow plug light goes out, the
relay de-energizes the glow plugs. Not true!
The glow plug relay keeps them on for quite a while after the vehicle
starts. I have a voltmeter in my old Panzerwagon and it stays under
12 volts for about 3 minutes or so, it seems, then the voltage returns
to the normal 13.8 or so.
And there is no relay circuit control tie in to coolant or head
temperature, so that the glow plugs go through the cycle again on
restarts, even if the engine is warm.
So when I go down to my rural post office and take 2 minutes to pick
up the mail, I just leave the engine idling so that the plugs do not
have to go through another heating cycle unnecessarily. It drives the
local environmental militants nuts.
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