I like to warm up the engine a little (but not a lot) before I start driving, and just realized that the afterglow light makes a perfect "timer." In relatively warm climates, 30 seconds of idling, especially with the glow plugs energized, is "warm enough." I glow the 603 for ten or fifteen seconds while I put on my seatbelt, start the engine and let it idle until the pre-glow relay turns off the glow plugs and the afterglow light at about 30 seconds (YMMV). Then I'm good to go. In a cold climate, 45 or 60 seconds might be better. I suppose that would give you time to scrape the ice off of the windshield.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

300SDL 603 emgine - Wired up the afterglow circuit but it seems that the 50C thermostat switch shown in the picture is not switching to ground. I turned off the engine after it reached operating temperature ( 80c-90c ) and measured the switch to ground and it was not conducting. I measured the voltage across the vacuum switch Y29 and I do not get 12V neither with engine running.

Questions:

1) Is it possible the thermostatic switch is faulty?
2) Does it mean Y29 was never switched on with the faulty 50C switch? What does this Y29 do to the tranny control in layman terms? Any harm done?
3) Shall I replace the 50c switch and try it again?
4) I measure the glow plugs run on time with the purple wire removed and it is about 30s, is it expected?

Thanks

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

That switch is used to soften the shifting of the transmission when the car is cold. The switch closes after 50 degrees is reached so if you tested it at operating temp, it shouldn't have power. My memory isn't what it used to be and I may have it backwards. I did this mod a few years ago. Of course it's possible it is faulty if it's 23 years old, but I don't think that's your issue.

__________________
1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

Bio300TDTdriver - thanks for the reply. The problem I find is that the 50 degrees switch is not closing, when it closes the connector goes to chassis (ground) and completes the 12 volts circuit for Y29. It may be faulty as it could be from new. I will pull and check it out.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Possibly but IIRC the switch is closed (continuous to ground) below 50*C and open above.

Do you get +12V at one of the connector pins at Y29?

Before coolant gets to 50*C, Y29 interrupts the boost signal to the tranny vacuum transducer. This softens shifts since there is no boost signal component to the vacuum signal to the tranny. Above 50*C the transducer integrates(?) the VCV vacuum signal and ALDA boost signal for optimal vacuum signal to the tranny modulator.

Flaring isn't good for the transmission. Otherwise a faulty 50*C switch shouldn't cause long term problems.

If you think of Y29 as a cylinder, it has an attachment at one end (the bottom end as installed) and two attachments at the other. The single attachment tees into the ALDA boost signal. At the other end, one attachment goes to the transducer, the other tees into the VCV (or transducer vacuum source?). With no power to Y29, there should be a clear path between the ALDA boost signal source and transducer. The other attachment should be blocked. With power to Y29, there should be a clear path between the two attachments at one end. The attachment at the far end should be blocked.

Sounds right.

The 50*C switch I removed when I converted to an afterglow relay has no impedance when cold sitting on a garage shelf. It would provide ground to Y29 when cold.

Sixto
87 300D

Sixto - You are right. The 50 degree C switch is 'Normally Closed'. For some reasons I thought it is 'Normally Open' just like others to turn on the aux fan. My design is all reversed. Now I have all the electrical characteristics I am expecting. Back to the drawing board and it should be OK now.

Thanks.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

After finding this useful thread it may me wonder if my '90 w124 300D has a stock afterglow setup or if I need to retro-fit. If a retro is needed I'm assuming that the GP relay needs to be changed. Any advice on the best relay to use? Thanks.

All 602 turbos have factory afterglow ('90-'93 300D and '87 190D turbo) in the US so, you already have it.

__________________

Gone to the dark side

- Jeff

See post #21. You already have it.

Jeff, you win.

__________________
1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

Thanks.

Thanks.

Then there is no reason to implement Jeremy's suggestion I take it?

PS - While trying to determine if my car had afterglow I found a $5 listing on eBay for a 81 - 85 glow plug relay if it helps anyone -

http://cgi.ebay.com/ebaymotors/MERCEDES-W123-300D-300TD-W126-300SD-OEM-Glow-Plug-Relay-/150592676970

Hello everyone,

Jeremy, I followed your instructions, but I think I may have a wrong relay for this project. Would you mind giving me relay diagram details or part # where I can buy it? I got mine at a junk yard. When I start the car, the wires in the compartment fuse (the ones going from the violet plug to fuse box) start smoking and melt together. I separated them and applied liquid tape a bit. Please help. Thank you!

Here are my images:

Your relay is the correct kind so it probably is wired incorrectly; I can't tell from your pictures. Using your relay, terminals 85 and 86 should be wired in parallel with the Y29 solenoid I mention in my first post of this thread. The violet wire from the preglow relay should be cut and the two ends connected to terminals 30 and 87.

If I understand the diagram on your relay, when the engine is cold (below 50C), thermal switch S25/6 is closed, powering solenoid Y29 and also your relay, through its pins 85 and 86. When the relay pulls in, according to the diagram on the relay, terminals 30 and 87 are electrically disconnected, thus "cutting" the violet wire. This forces the preglow relay to stay on until its internal timer turns it on, about 30 seconds.

When the engine warms up above 50C, switch S25/6 opens, turning off solenoid Y29 and also your relay. This reconnects the violet wire so that the preglow relay stops as soon as you release the key from the "start" position. With the engine warm you don't need afterglow.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

It's 87a, correct? You mentioned 87 and I do have that one too so wanted to make sure. The diagram on my relay just looks different than the one on yours. There looks to be an extra diode. I did a test...when I turn the key and put my finger on the relay, I hear one click instantly. Should there be a second click in another few seconds?

It's 87a, correct? You mentioned 87 and I do have that one too so wanted to make sure. The diagram on my relay just looks different than the one on yours. There looks to be an extra diode.

Also another question. On last image, after you were finished, your relay had one unused pin. On another picture it looked like you used all 5 pins as it had a red connector.

You are correct, pins 30 and 87a should be the correct ones to use on your relay.. Pin 87a is "normally closed." The diagram on your relay is somewhat misleading, so I wrote "87 and 30." In fact, those pins should NOT be connected when the relay is energized. Connecting the violet wire through those pins "breaks" the wire if the engine is cold (under 50C) so that the preglow relay stays on for the full time. Using pin 87b will have the opposite effect. My relay works the same as yours even though the diagram may be different.

The relay has no diodes at all. The little box-figure in the diagram on the relay that bridges the coil is a capacitor. It absorbs the surge when the relay de-energizes, thus minimizing sparking at the switch contacts and consequent erosion of the switch contacts.

If the engine is cold, the relay should click once when you turn on the key, no more. If the engine is hot (over 50C) the relay should not click at all.

The red connector on the 5th pin in my relay is unconnected; it's there to prevent accidental short circuits.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970