Glowplug light - PeachParts Mercedes-Benz Forum

JWJ · #1 10-24-2006, 10:55 AM

When I turn the ignition on my '83 MB 300D the glowplug light always comes on. No problems starting even in cold weather.

Last spring when it started getting warm the glowplug light on my '85 MB 300TD stopped lighting up. I assumed it was at least one bad glowplug. I forgot about it until now (when its cold). I assumed I'd have to replace glowplugs but to my surprise the glowplug light is now working again. No trouble starting even in cold weather.

Seems on the '85 300TD the glowplug light only comes on when its cold enough to need it.

So do the glowplugs lights on a '83 300D and a '85 300TD really work differently? How are they different?

sokoloff · #2 10-24-2006, 01:03 PM

Glow plug light should always come on, if only for a second or two in hot weather. Take an ohm meter to the glow plug terminals at the relay and test them. Good plugs measure about 0.6 ohms cold. You likely have a bad one or weak one.

Len

vstech · #3 10-24-2006, 01:47 PM

From what I have read, here and other places, even the modern 606 GP relay will post a GP light for a second or two in hot weather. if no light at all when the key is first turned, start searching for a bad plug. or a bad ground to the block. also, the GP fuse can have a crack that allows power sometimes and denies it others... so a new fuse strip would not be out of line.
good luck.
don't forget dieselgiant's site for GP testing procedures.
John

Jadavis · #4 10-24-2006, 01:51 PM

http://dieselgiant.com/mercedes_diesel_maintenance_tips.htm

About 1/2 way down is the section on glow plugs.

4 of my 6 are shot, 2 are reading about 1.4 ohms. I'm replacing all of them. Man, is the 603 engine a pain to work on! I'm pulling the intake manifold to get to the glow plugs. While I am there I am going to play with the ALDA, add injection line heaters, replace the injector fuel return lines, clean things up, and look around.

What the heck do you use to get the gunk out of the intake manifold and cross over pipe?

-Jim

riethoven · #5 10-24-2006, 02:04 PM

Quote:

Originally Posted by Jadavis

http://dieselgiant.com/mercedes_diesel_maintenance_tips.htm

About 1/2 way down is the section on glow plugs.

4 of my 6 are shot, 2 are reading about 1.4 ohms. I'm replacing all of them. Man, is the 603 engine a pain to work on! I'm pulling the intake manifold to get to the glow plugs. While I am there I am going to play with the ALDA, add injection line heaters, replace the injector fuel return lines, clean things up, and look around.

What the heck do you use to get the gunk out of the intake manifold and cross over pipe?

-Jim

Soak it in some mineral spirits and that will loosen up the sooty residue. I have heard that it is all from the EGR or leaking valve stem seals. You could also try Simple Green but I don't think it will cut that residue like mineral spirits.

Jadavis · #6 10-24-2006, 03:11 PM

Keep in mind that I have an aluminium intake and cross over. I'll check to see if mineral spirits and aluminium play well together.

Right now the bottom 1/3 of the the intake is submerged in a bucket with biodiesel, simple green, purple power, and some orange foaming degreaser in it.

I tried a scrub brush. It worked but now I have a scrub brush full of gunk and it will not pick anymore up! I'll just keep letting it soak until I am done working today. Maybe by then something will have happened to the gunk in the bottom 1/3rd.

Sorry about the thread hijack!

-Jim

riethoven · #7 10-24-2006, 03:18 PM

Quote:

Originally Posted by Jadavis

Keep in mind that I have an aluminium intake and cross over. I'll check to see if mineral spirits and aluminium play well together.

Right now the bottom 1/3 of the the intake is submerged in a bucket with biodiesel, simple green, purple power, and some orange foaming degreaser in it.

I tried a scrub brush. It worked but now I have a scrub brush full of gunk and it will not pick anymore up! I'll just keep letting it soak until I am done working today. Maybe by then something will have happened to the gunk in the bottom 1/3rd.

Sorry about the thread hijack!

-Jim

Aluminium and mineral spirits are compatable. I worked on Alfas for years and they are all aluminium and I have mineral spirits in my parts washer. Although I have heard that biodiesel is an excellent degreaser. When I was a kid, I used to put parts in the dishwasher, especially carburator parts, it would get them spotless.

Maybe try and scrape as much of the gunk off that you can before you start with the brush, so you don't load the brush up as quickly.

KCM · #8 10-25-2006, 01:17 PM

[QUOTE=JWJ;1311839]Last spring when it started getting warm the glowplug light on my '85 MB 300TD stopped lighting up. I assumed it was at least one bad glowplug. I forgot about it until now (when its cold). I assumed I'd have to replace glowplugs but to my surprise the glowplug light is now working again. No trouble starting even in cold weather.[QUOTE]

I agree with the others, the light should come on if only for a couple seconds. I'm fairly certain that if a glow plug is bad the light should flash, not go out completely. This would indicate a lose of power to the glow plug relay, or could simply be a loose or bad bulb (or bad socket ground) in the dash. Being you said it still started fine, I would lean heavily in the bulb direction.

DigitalDave · #9 10-25-2006, 10:57 PM

On my '95 300D (plugs replaced in July; new engine wiring harness in Aug) the glow plug lamp has started to act odd. Car starts and runs fine. When cold, lamp comes on, I wait about 15 seconds (lamp goes out a bit soooner) and then start--all is fine. But sometimes when warm (at op temp)....no lamp, I wait 15 seconds...starts fine...and *then* the lamp comes on. I turn off the engine, turn the key to "glow" and lamp comes on, starts, and then goes off. Occasionally lamp comes on while crusing on highway...and then goes off. Checked plugs w ohmmeter--all about .6 except #5 about 1 ohm. Relay contacts clean and snug. Any ideas? Loose glow plug connector at glow plug?