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1982 Mercedes Benz 300D Dark Blue
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41 Posts
Discussion Starter #1
hello, does anybody have this problem or know if this is normal. 1982 300d, w/140,000 mi. when turning over a cold engine ( ambient temp 70 deg f) my glow plug light comes on for only about a second or even less then goes out. car starts good everytime. i had a '85 300d with 220,000 mi and in same operating conditions the glow plug light would stay on for about 4 seconds. could the short light duration of a second or less be indication of bad info or temp reading from something else. any help or suggestions would be good. i have checked the relay and it has power and the continuity seems to be okay from the connector to the plugs with them installed in the moter. i have not yet pulled out the plugs to check them due to the car starts okay with every attempt. thanks, G
 

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'73 450SL, '83 300CD, '01 E320 4matic
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2,446 Posts
Welcome to the forum.

You should fill out your profile when you get some time to let us know where you're from, and what you drive (even though you mentioned the car in the post).

If your car is starting fine with little effort, chances are everything is ok. Is it starting well even in cold weather?

1 second does seem like a short duration.

In order to correctly test the glow plugs, you need to not test continuity, but test the resistance of the plugs. Around .5 ohms is correct. .4-.7 or so ohms would be reasonable.

Make sure you compensate for an error in your meter when you're doing tests of such low resistance. (in other words when you short your meter leads together, you may see a reading of .3 ohms for example. If you get a reading of .8, the actual reading is .5.

I hope that makes sense.

Continuity on a plug would be 0 ohms, which would be a shorted plug. A shorted plug will not work.

My vehicle had a short glow plug duration when I had 3 bad GPs. I would definitely suggest testing them.

Unplug the cable from the relay, and just test them between the engine block and the 8mm nut on the GP.
 

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1982 Mercedes Benz 300D Dark Blue
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41 Posts
Discussion Starter #3
thanks Aaron, i will give that all a try when i have time, yes it does make sense. i added info to profile as per request. just got this car and doing lots of stuff with it right now. when i get to the glow plugs i will post results. thanks again, gary.
 

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'81 240d
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229 Posts
That does seem like a short glow time-- I learned the other day that you can listen for the relay to 'click' after the glow light goes out, and I think that's when the glow plugs actually stop getting juice.. I can hear it click from inside my car, but you should have time to run out and put your ear up to the relay if you can't. My light usually goes out after 4 seconds, but the relay clicks after 30.
 

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2013 MINI Copper S Clubman, '84 300CD-weekend car
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10,152 Posts
^^Yes the juice stays on till you hear the click.
The PO needs to check his glow plugs, the same thing happened to me, after installing new ones, problem solved.
 

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1982 Mercedes Benz 300D Dark Blue
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41 Posts
Discussion Starter #6
thanks for the previous responses, i have 5 new bosch glow plugs coming in from autohausaz.com, i will update later next week, should have time to put them in by thursday. thanks again, guys.:thumbsup:
 
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