Do all GP's fail if one goes out?

[GRIESL]

Second time this has happened to me--#1 GP goes out and seems to take 'em all out. At least the dash light doesn't come on and it's a b&%$# to start--seems like no glow at all. So if one gp goes out, does that somehow prevent juice to the rest? Or does #1 has some special powers? i.e. if #5 went out would the dash light still come on? I just fixed it, so no big deal, but I'm curious. Thanks.

[DeliveryValve]

If your talking about your '85, then No. The GPs theoretically should burn out separately and the unburnt plugs should be still working. But if you have the older loop style glow plugs, then they are wired in series in which all will go out if one doesn't work. But not necessary that all will be burnt out.

[lietuviai]

The 85's did not have the loop style GP's. I had two burnt out GP's on the 85 I had and it still started. I don't remember which ones were burned out though and I still had a working GP light.

[raslaje]

Originally Posted by lietuviai

The 85's did not have the loop style GP's. I had two burnt out GP's on the 85 I had and it still started. I don't remember which ones were burned out though and I still had a working GP light.

I think if the GP light doesn't come on it's a sign of bad glow plugs. At least that's what I concluded last winter when the GP light would not come on and I couldn't start the engine. One glow plug measured open (infinity) and others measured higher than approx 0.5 ohm (only 1 measured approx .5 ohm IIRC). Replaced all 5 glow plugs, engine started, glow plug light worked.

[GRIESL]

Thanks, guys, for all the replies. So, do you know if the #1 is more prone to burning prematurely. All the plugs were brand new about 15k ago. Thanks.

[Matt L]

If #1 or two or more of #2-#5 goes out, the lamp will not illuminate. There are two current sensors in the relay (one on #1, one on the rest).

#1 is not more prone to burn out. But any part can fail.

[JWJ]

OK, refresh my memory, GP#1 is the closest to the front of the car or the passenger compartment?

[Matt L]

Cylinder 1 is the furthest from the flywheel. That's at the front of your Benz.

[toomany MBZ]

When my light did not come on at all, I checked with an ohm meter, only #1, nearest to radiator, was bad, but I replaced 'em all, light back to normal.

[Brian Carlton]

Originally Posted by Matt L

If #1 or two or more of #2-#5 goes out, the lamp will not illuminate. There are two current sensors in the relay (one on #1, one on the rest).

#1 is not more prone to burn out. But any part can fail.

This is correct.

[JimSmith]

On my 1982 240D when one glow plug was burned out, the light would work if you cycled the key again. If more than one plug was burned out, cycling the key did not make the dash indicator light work. Jim

[Bruce Bonds]

84 300D. Glow plug light not working. Car would not start on cool mornings. 40 degrees F. Changed all 5 glow plugs. I jump tested the old plugs and only two were dead. When I first tried the job, I almost gave up because of the lack of space to wrench. Then I read several ShopForum posts on the subject. Thanks to the member that suggested removing the metal fuel lines and one piece of throttle linkage. That made the job very easy. I also suggest using rachet type box end wrenches in 8 mm and 12 mm. It will also help to stuff a rag in the space below the plug to catch any dropped wrenches and bolts. Mission accomplished: the car starts with one glow cycle and the light works as it should.