I searched and can't find the simple method of testing glo plugs. I have a multi-meter for testing.

I suspect one is giving me fits.

Thanks

Don

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'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
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less than 1 ohm resistance is OK, more its NG

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Ohm's Law states the V=I*R (v-voltage, r-resistance, i-amps) or R=V/I. All electric heaters work on this principal of using a high resistace coil or wire to create heat, GP's being no exception. A 12 volt system would need a hell of alot of power flowing through to heat up those plugs at 1 ohm of resistance. I could be wrong, but I would tend to think that our GP's have extremely high resistance to heat up to over 1000 degrees that they do. Someone want to chime in and correct me if I'm wrong?

__________________
Adam Lumsden
(83) 300D
Vice-President of the MBCA International Stars Section

Hes right 1 Ohm or less...

I think you need to follow the equation to completion Adam.

1 Ohm or less = 12volts / XX amps....

So your car's system would need to produce at least 12 amps or high to keep it balanced. That's enough heat to ignite diesel, which perpetuates the the glow plug to contimuesly ignite the system. The combustion of the diesel heats the engine block, not the glow plugs...

Your right I didn't take into account the volatility of diesel, and the primary function of the GP's in the first place.

__________________
Adam Lumsden
(83) 300D
Vice-President of the MBCA International Stars Section

Cheers....

You have Ohm's law right, but I think you might be misunderstanding the consequences of it.

Consider that power is equal to VI (is equal to I^2 x R). If one has a fixed, low voltage (as we do with our 12V automotive systems,) and one needs (relatively) high power, then one needs (relatively) low resistance in order to get (relatively) high current. This is why cars need such big, fat cables to do any heavy work.

Ohm's law also explains why the starter motor circuit is sensitive to what might seem to be modest resistances from less than proper connections. The required current is high enough that the voltage drop across such a connection (Ohm's law works here, too) is significant. If someone says that the connections are fine because they "beeped them" for continuity with their meter, well, they haven't really said much.

As an aside, I think the resistance of the glow plugs increases with temperature, so it doesn't necessarily tell one directly what the "terminal" resistance during glowing is - I think it increases as they heat. The FSM has some graphs, if I recall correctly, showing how the temperature ramps up.


-- eskimo

This is correct. If you have five glow plugs, each with a cold resistance of .5 ohms, each plug will flow 24 amps. 5 plugs in parallel will flow 120 amps. Since the fuse is rated at 80 amps, the plugs must immediately increase in resistance within seconds of the current application to prevent the fuse from melting.

This is entirely true, that is why YOU MUST test the glow plugs when the engine is cold otherwise they will give you a higher resistance value.
internal resistance falls as glow plug temp rises which leads to a lower current flow. a new glow plug at engine operating temp has a resistance of about 100ohms

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Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32

Heres the sure way: Remove glowplug. Apply 12volts to the terminal with ground attached to the body. Plug should glow red hot in just a few seconds. Not a dull red or just get hot. Red-orange hot like an electric range top element. I have had them test fine with a meter and not glow red hot. Only way to be absolutely sure if you have doubts is to pull them out and test them. RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

First, these 616, 617 engines operate the pencil glow plugs at 11 volts.

Remove the lead then use an OHM meter to test....

If it's been a few years or you have no idea of the last change, replace them...

hehe.. Mine are original at 270K, could that be the cause of my little stumble right after cold start?

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1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

You guys overestimate me. I needed to know the actual process. Like where to put the wires from the tester, etc.

However, RT gave me a good lead. I'll yank each one.

Thanks for all the info....

Don

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DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
'82 240D 229k (Matt's - Converted-300DT w/ 4 speed

Don,

You can test them in place. their resistance should be very low. On the order of 1 ohm, give or take, depending on the accuracy of the meter. Most handhelds aren't that accurate at that low of a range. Don't use a continuity beeper, most will beep with resistace as high as 40 ohms.

There is a connector that you can disconnect that will give you access to the plugs via the wire connecting to them. You can check the resistance from the socket in the connector to the engine block (or head). Check them one at a time, or check each plug at the threaded tip with reference to the block.

Good luck

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

The pencil type are easy to test - I just pulled each one and applied 12V. If it glows it's good. The other type are more tricky, but once you remove the wires, using the multimeter it should register as a short. If it's not a short, it's no good. And when you pull it, the loop will be broken.

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'83 240D with 617.952 and 2.88
'01 VW Beetle TDI
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