Afterglow and the Violet Wire - Page 8 - PeachParts Mercedes-Benz Forum

gsxr · #**106** 12-18-2008, 05:28 PM

Quote:

Originally Posted by sixto

Isn't it just as likely the timer circuit in an afterglow relay will fail? What's the difference?

Could be, Sixto. The relays have different construction... the old type is more discrete/mechanical, the new one is IC-based. See photo below. I have no idea which has a better reliability record though.

kerry · #**107** 12-18-2008, 05:56 PM

Quote:

Originally Posted by Old300D

Last year I was trying to start my 300D (with old loop style plugs) in the cold. Of course it had a weak battery, but the glow circuit really pulled the current. I would think one reason the plugs shut off while cranking is to get all the battery power directed into the starter motor.

One consequence of severing this start signal could be less cranking ability, especially on the loop style plugs, as they are extremely inefficient, putting half their heat outside the engine.

Just a thought I had reading this thread. I'm now driving a 240D with the pencil type plugs and a standard plug relay. Yesterday after work, the temperature had dropped to the high 20s (F), and it fired right up after leaving the plugs on right up to the point where the relay times out. A new battery helps out a lot though.

Don't know if anyone else responded to this post, but just to clarify, the violet wire does not cut short the timed glow plug cycle until AFTER the key is released from the 'Start' position. The glow plugs are activated during the cranking cycle.

Jeremy5848 · #**108** 12-18-2008, 06:17 PM

Quote:

Originally Posted by sixto

Isn't it just as likely the timer circuit in an afterglow relay will fail? What's the difference?

Sixto
87 300D

If you have an "afterglow" light in your instrument cluster, it will alert you to a failed-on preglow relay.

Jeremy

Bio300TDTdriver · #**109** 12-18-2008, 08:10 PM

Jeremy,

If you don't stop coming up with new tricks, I'm going to have to block your post.

Now I have another project to do, afterglow indicator.

Chris

Quote:

Originally Posted by Jeremy5848

If you have an "afterglow" light in your instrument cluster, it will alert you to a failed-on preglow relay.

Jeremy

kenstfelix · #**110** 12-19-2008, 01:48 AM

I'm going to do this and I want to put in a manual switch so I can turn the afterglow off when the car is warmed up. How many amps should the switch be rated for?

retmil46 · #**111** 12-19-2008, 03:30 AM

On the red '87, once I'd repaired the violet wire and done away with the poor mans afterglow, a cheap cigar lighter plug-in voltmeter took most of the guess work out of cold weather starting.

With a good set of glow plugs and a good battery, initially they would whack even that Group 45 battery down to 10.8 volts. After a little experimenting, I learned that if I waited for the glow plugs to get hot enough for the battery voltage to rise back up 11.6 volts, the car would fire up without any issues even in mid 20 temps. Granted, in mid 20 temps it usually took one complete cycle and part of another to get them warm enough to reach this point.

kerry · #**112** 12-19-2008, 09:28 AM

Quote:

Originally Posted by retmil46

On the red '87, once I'd repaired the violet wire and done away with the poor mans afterglow, a cheap cigar lighter plug-in voltmeter took most of the guess work out of cold weather starting.

With a good set of glow plugs and a good battery, initially they would whack even that Group 45 battery down to 10.8 volts. After a little experimenting, I learned that if I waited for the glow plugs to get hot enough for the battery voltage to rise back up 11.6 volts, the car would fire up without any issues even in mid 20 temps. Granted, in mid 20 temps it usually took one complete cycle and part of another to get them warm enough to reach this point.

That is a very interesting technique. Where did you purchase the plug in voltmeter?

retmil46 · #**113** 12-19-2008, 10:03 AM

Quote:

Originally Posted by kerry

That is a very interesting technique. Where did you purchase the plug in voltmeter?

You can find them all over - Advance, Autozone, Wally World, etc. Around $10 if I remember correctly.

That simple voltmeter has saved my rear more than once when it came to keeping that car running. It's what alerted me in the first place that my glow plugs were still on after 30 miles of freeway driving.

IMHO that is the one glaring flaw in the instrumentation on these cars - no installed voltmeter. After what I've seen over the last 2 years, on these cars it's not just nice to have, it's essential equipment IMO.

kerry · #**114** 12-19-2008, 10:15 AM

Quote:

Originally Posted by retmil46

You can find them all over - Advance, Autozone, Wally World, etc. Around $10 if I remember correctly.

That simple voltmeter has saved my rear more than once when it came to keeping that car running. It's what alerted me in the first place that my glow plugs were still on after 30 miles of freeway driving.

IMHO that is the one glaring flaw in the instrumentation on these cars - no installed voltmeter. After what I've seen over the last 2 years, on these cars it's not just nice to have, it's essential equipment IMO.

Just ordered one on Amazon. Voltmeter and a vacuum gauge.

compu_85 · #**115** 12-19-2008, 11:25 AM

Quote:

Originally Posted by Jeremy5848

If you have an "afterglow" light in your instrument cluster, it will alert you to a failed-on preglow relay.

Jeremy

Hmm... I could use the open red spot in my instrument cluster for that...

-J

Jeremy5848 · #**116** 12-19-2008, 01:08 PM

Quote:

Originally Posted by kenstfelix

I'm going to do this and I want to put in a manual switch so I can turn the afterglow off when the car is warmed up. How many amps should the switch be rated for?

I've never measured the current but since it is only a signal wire, probably only a few milliamps, so any switch that can handle 1 amp or more will be fine. There are some tiny toggle switches, perhaps available at Radio Shack, for example, their part number 275-626. You could hide it anywhere in the dash area, no one would ever see it.

Jeremy

Jeremy5848 · #**117** 12-19-2008, 01:22 PM

Quote:

Originally Posted by compu_85

Hmm... I could use the open red spot in my instrument cluster for that...

-J

Yes, that's what I did. In the case of my '87, the open spot was green. If the light is on, the glow plugs are energized (or at least #1 is, that's where the light is connected).

Jeremy

compu_85 · #**118** 12-19-2008, 08:23 PM

How did you make that label?

-J

retmil46 · #**119** 06-04-2012, 12:04 PM

OK, I've no reason to doubt gsxr's word when it comes to technical matters - he helped me out immensely on my first (now wrecked) 87 300D -

but just to assuage an old man's suspicions, are you guys sure that Beru GN-909's will work in an 87 300D with vertical injection?

That's what the PO sent along with the present car 3 years ago as spares, and it kinda freaked me out yesterday when I looked up their P/N, and it said they were for a '93 2.5 L Range Rover diesel!!

Let's just say that other "items" I've found on the car over the past few months, have given me reason to do a little double-checking as I've been going over it.

A side note - I discovered checking online that at least a couple of the auto parts chain stores list the Bosch 80031 (23 mm plugs) as being the correct replacement, instead of the Bosch 80006 (25 mm plugs), for an 87 300D - so be forewarned if you need to pick up a set locally over the counter.

gsxr · #**120** 06-04-2012, 12:27 PM

I'm 99% sure about the GN-909 fitment, as noted in my cross-reference document. However I've never personally purchased a set to verify this. From memory, I think I had checked with some Beru documentation that did check out as correct for 25mm OM60x plugs. It's also possible they fit other applications like the Land Rover too.

retmil46, btw - I sent you an email, pelase let me know if you don't receive it!