Testing Glow plugs? - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 12-01-2011, 04:30 PM Thread Starter
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Testing Glow plugs?

My wife's 1976 240d has been reluctant to start on these colder mornings.

I pulled one of the glowplugs hoping that I could test it and all I managed to do was to create lots of sparks.

On other cars I have just touched the body of the glow plug to the negative terminal and run a lead from the positive to the threaded end.

What am I doing wrong?

Also, how long should it take to glow?

I have attached a picture showing the type of glow plug that I have.

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post #2 of 3 (permalink) Old 12-03-2011, 05:53 AM
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Do a search on this page. Glow plugs are tested with an ohm meter.
Diesel Giant.com also has a how-to on testing plugs.
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post #3 of 3 (permalink) Old 12-04-2011, 03:49 PM
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These old glow plugs are 0.9 V, which mean you cannot test them directly on 12V. They are wired in series, together with resistance wires.

If they are broken, you get an ifinity reading if you do a resistance reading.

The glow system and how to test them is described in the FSM:
15 Electrical System Engine (Preglow) - OM616
and there click:
15-505 - Operation of preglow system
15-510 - Checking preglow system
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