Glow Plug pimpage, a different approach.

[wolf_walker]

Observe section H in this section of this FSM.

https://www.box.com/s/d13jzf7prcr1udgpdtv9

This is the glow plug relay, and essentially the whole system, for a
post 80 or so W123 with the OM617 5cyl or 616 4cyl (300D/240D)


This is a proven system that is generally quite trouble free and robust,
and nearly as important to me, is mechanically and electrically elegant
and exhibits classical German engineering and is the culmination of a number
of iterations, as you can read in the previous sections before H.
I've owned a number of these cars and never had a moments trouble other than a
single glow plug that died, which was easy enough to check since they are on separate
lines in a connector.  The NTC sensor is integral to the relay, as is the fuse.  The relay
has basic self diagnostic functions detailed in the FSM in that if a single GP fails
it will not illuminate the GP light as warning.  There is an afterglow feature, and a time
based safety cut-off.  Also there is a simple and common modification to the relay that will
illuminate the GP light at a lower level to show after glow, which is a true representation of the
actual current receiving state of the GPs.

They are pretty cheap used, and there are probably 10 of them for every VW around, and
aren't crazy expensive new, nor will they become unavailable in the foreseeable future.

Seems like a no brainer to me, unless I've overlooked some reason it can't be used on a
4cyl VW-D.

Objections to dicking with the stock setup would be, and I've voiced them quietly before, that the stock VW setup frequently works fine, and when
it does not there is generally an outside reason.  I have had a 650K and have a 400K example, and numerous
250Kish VW-D's and every one of them had completely normal stock GP systems with all stock components for many years, since new in fact.
Maybe I'm just lucky.  I also appreciate the huge gnarly wire with a ford starter relay with a manual switch approach, or any variation of
to get the current out of the fuse box.  I wouldn't have designed it the way VW did, even though it usually works in my experience.
I'd have done just what Mercedes did, hence this thought.
The only less than ideal thing I can find here is wire size, and it's been my experience from owning a few of and working on a lot of, that
Mercedes back in that era did not cut corners on BS like that, if it needed a larger wire, it would have gotten one.
Nor do know exactly how the GP temp relates to voltage, as I've seen quoted with the stock system (but never measured) as less than
the ideal of battery voltage.  If anyone has ever checked it with something able to measure north of 900F at varying voltages I'd be interested
to hear it.  There is also some pertinent info in the FSM I linked above about target temps, for the Merc motors at least.

I've pondered this for many years, since I had spare Merc stuff around, but never got around to it largely since I've never
had a problem with the stock VW system.
Still looks like a neat project though and I hope to get to it shortly.

Thoughts?

[745 turbogreasel]

The MB  electrical connector  is really nice, Ii have had similar thoughts, though my  factory system has given me very little trouble.

[wolf_walker]

MB used to sell those plugs in various pin numbers cheaply, they used them all over (which was wonderfully logical) and little solder-on pin kits for making/repairing.
I'll poke around and see if they still exist, especially the pins otherwise it'll be wire splicing unless I buy a complete used harness, that might be excessive.
The really old one's were bakelite, I think my 73 W114 still used them, by the W123 time they were plastic near as I remember.

[745 turbogreasel]

It's pretty easy to pop used ones apart and swap  pins/wires around.

[wolf_walker]

Yeah, should be able to un-solder the wires from the pins too.

[92EcoDiesel Jetta]

My thoughts with the Mercedes relay is too much work and no real gain. The stock VW system works just fine. If you want to make it more reliable and easier to service, convert the stock VW glow relay to manual control (advantage: no hacking into the stock wiring), replace the copper bar with four individual wires. Done! I've gone one step beyond that and added a button on the glow relay to manually push on the contacts in case the manual control or switch ever fails. Last ditch is a 8 gauge alligator clip to jumper the glow plugs to battery + terminal.

 The stock wiring has adequate wire size to supply sufficient current / voltage to the glow plugs to start the engine. Why mess with it? Using heavier gauge wire and shortening length from stock will increase voltage/ current to the glow plugs and make them run hotter but will also shorten their life. Why do it?

FYI glow plugs run way north of 900 F, try doubling it. The link you provided says 900 to 1000 C.

1000 C is 1832 F.

Observe section H in this section of this FSM.

https://www.box.com/s/d13jzf7prcr1udgpdtv9

This is the glow plug relay, and essentially the whole system, for a
post 80 or so W123 with the OM617 5cyl or 616 4cyl (300D/240D)


This is a proven system that is generally quite trouble free and robust,
and nearly as important to me, is mechanically and electrically elegant
and exhibits classical German engineering and is the culmination of a number
of iterations, as you can read in the previous sections before H.
I've owned a number of these cars and never had a moments trouble other than a
single glow plug that died, which was easy enough to check since they are on separate
lines in a connector.  The NTC sensor is integral to the relay, as is the fuse.  The relay
has basic self diagnostic functions detailed in the FSM in that if a single GP fails
it will not illuminate the GP light as warning.  There is an afterglow feature, and a time
based safety cut-off.  Also there is a simple and common modification to the relay that will
illuminate the GP light at a lower level to show after glow, which is a true representation of the
actual current receiving state of the GPs.

They are pretty cheap used, and there are probably 10 of them for every VW around, and
aren't crazy expensive new, nor will they become unavailable in the foreseeable future.

Seems like a no brainer to me, unless I've overlooked some reason it can't be used on a
4cyl VW-D.

Objections to dicking with the stock setup would be, and I've voiced them quietly before, that the stock VW setup frequently works fine, and when
it does not there is generally an outside reason.  I have had a 650K and have a 400K example, and numerous
250Kish VW-D's and every one of them had completely normal stock GP systems with all stock components for many years, since new in fact.
Maybe I'm just lucky.  I also appreciate the huge gnarly wire with a ford starter relay with a manual switch approach, or any variation of
to get the current out of the fuse box.  I wouldn't have designed it the way VW did, even though it usually works in my experience.
I'd have done just what Mercedes did, hence this thought.
The only less than ideal thing I can find here is wire size, and it's been my experience from owning a few of and working on a lot of, that
Mercedes back in that era did not cut corners on BS like that, if it needed a larger wire, it would have gotten one.
Nor do know exactly how the GP temp relates to voltage, as I've seen quoted with the stock system (but never measured) as less than
the ideal of battery voltage.  If anyone has ever checked it with something able to measure north of 900F at varying voltages I'd be interested
to hear it.  There is also some pertinent info in the FSM I linked above about target temps, for the Merc motors at least.

I've pondered this for many years, since I had spare Merc stuff around, but never got around to it largely since I've never
had a problem with the stock VW system.
Still looks like a neat project though and I hope to get to it shortly.

Thoughts?

[wolf_walker]

I covered all that, pro and con, I believe, and thank you for the correction.

Anyone else?  I've thought out both sides of this pretty well but I figured there was something I had missed.

Sent from my SCH-I535 using Tapatalk 2

[8v-of-fury]

My thoughts with the Mercedes relay is too much work and no real gain. The stock VW system works just fine.

I wouldn't say fine, it worked and that was about it. 12v plugs getting <8V.. not proper. Anything, whether it be manual starter relay or another manufacturers OE setup, to get more juice to the plugs. Who cares how ya do it? Just get it done.

[bbob203]

Who needs glowplugs when you have an mtdi? 

[wolf_walker]

My thoughts with the Mercedes relay is too much work and no real gain. The stock VW system works just fine.

I wouldn't say fine, it worked and that was about it. 12v plugs getting <8V.. not proper. Anything, whether it be manual starter relay or another manufacturers OE setup, to get more juice to the plugs. Who cares how ya do it? Just get it done.

10.5v on mine. If a stock system isn't managing that something is wrong. I never checked amperage, never had need to.

But yeah :-)

What I'd like to see is gp temp at 10, 11 and 12v, but not bad enough to rig up to test it. I should probably Google a bit.

A large part of my interest in this project is because of the elegance of an inclosed system. The, granted limited, self diagnostic ability (which is electrically slick, read the fsm section) is "neat", so is the internal temp sensor, as are the separate lines to the GP's, and the ability to trouble shoot the entire system from right there at it with a meter in no time.
The VW solution works, but getting there, as they say, is half the fun.


Part of my I interest in Euro cars is the engineering and philosophy behind there systems. VW was budget limited in many areas by the Rabbit era so they are a little short on that at times.

Sent from my SCH-I535 using Tapatalk 2

[92EcoDiesel Jetta]

I'd suggest rigging up a test yourself. Do you believe everything you find googling? You may end up with some yo-yo using an IR thermometer and gets the numbers wrong, by a factor of 2!

Another thought on adapting the Mercedes glow plug controller is the polarity/ logic for the glow light may be different. VW use a LED, Mercedes an incandescent bulb, it may or may not work. I can tell you for certain the half dim after-glow indication will not work with a LED.

Sounds like you are intent on doing it. Have fun and go for it!

My thoughts with the Mercedes relay is too much work and no real gain. The stock VW system works just fine.

I wouldn't say fine, it worked and that was about it. 12v plugs getting <8V.. not proper. Anything, whether it be manual starter relay or another manufacturers OE setup, to get more juice to the plugs. Who cares how ya do it? Just get it done.

10.5v on mine. If a stock system isn't managing that something is wrong. I never checked amperage, never had need to.

But yeah :-)

What I'd like to see is gp temp at 10, 11 and 12v, but not bad enough to rig up to test it. I should probably Google a bit.

A large part of my interest in this project is because of the elegance of an inclosed system. The, granted limited, self diagnostic ability (which is electrically slick, read the fsm section) is "neat", so is the internal temp sensor, as are the separate lines to the GP's, and the ability to trouble shoot the entire system from right there at it with a meter in no time.
The VW solution works, but getting there, as they say, is half the fun.


Part of my I interest in Euro cars is the engineering and philosophy behind there systems. VW was budget limited in many areas by the Rabbit era so they are a little short on that at times.

Sent from my SCH-I535 using Tapatalk 2

[92EcoDiesel Jetta]

My thoughts with the Mercedes relay is too much work and no real gain. The stock VW system works just fine.

I wouldn't say fine, it worked and that was about it. 12v plugs getting <8V.. not proper. Anything, whether it be manual starter relay or another manufacturers OE setup, to get more juice to the plugs. Who cares how ya do it? Just get it done.

If you are only getting 8V to the plugs with the stock system, something is wrong. Bad battery? Dirty connections? The Duraterm glow plugs for idi VW's are 11V plugs I believe, not 12V. If you manage to get 12 V to the plugs with heavy enough wires, you will shorten their life.

[92EcoDiesel Jetta]

BTW, I have a few 240D glow plug controllers if you need one. I may even have a mating plug.

[wolf_walker]

One takes the Internet, like this forum, with a grain of salt and the understanding that it's often worth what they paid for it (very little).
However an important modern skill for any technician is the ability to sift and judge the quality of info online quickly.  I'm pretty fair at it.
As it happens I read a few cool tech papers from Bosch and Beru but none of them mentioned temp VS voltage, only temp over time on.
Vague reference to not over-volting, especially the newer 6v plugs and such, but otherwise nada.
Interesting on the Duraterms being 11v, haven't seen that but will check it out.

I don't have anything myself that will read that high, so I'm not help at the moment.
What I do know, is that 10V or so provides perfectly fine starts with duraterms on my motor.
It's in the 50's here but same truck/same parts started fine in the low 40's last winter, so that seems
to be sufficient. 

I can work around the glow LED, but thank you for pointing it out.
I actually have TWO late 300D relays I've been trying to get someone to swap me
for a 240D part.  I could use the 300D piece but I'd have to fake the resistance across the 5th plug
to keep the self diag function so it would be messy.  Unless I make it an intake air heater.. 
I'm kidding.  I think.
If I don't rummage up a 4banger relay I'll yell, the plugs look to be harder to find than anything.
I miss my east coast junkyards, I'd have all this stuff already for $20.