On my '87 300D, I pulled the glow-plug relay, noticed an adjustment with a lock-nut. Is this for time? Temperature? Nothing at all? Anyone know?

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Gone to the dark side

- Jeff

Doubt many if any members have been fixing their glow plug relays. I have been tossing my bad ones and getting replacements from the salvage cars. As you suggest the adjustment is for something. Even if only to compensate for off tollerence components during the manufacturing process.
Your question did stimulate me to consider repairing mine. If I had to buy a brand new one to replace it once it failed. It certainly could not hurt anything. If the relay coil is not burnt up or open and the contacts still good a guy should have a chance.

Reason I wonder, ... the one in my driver shuts the light off after a few seconds, regardless of temperature. I glow it longer, started right away today at 1*F with one glow cycle, so I know it's working fine, would love to figure it out. So, ... I was looking at my spare that I haven't yet installed, and noticed the big adjustment screw between the plugs, ... I guess I could tweak the old one before removing it to see what changes if nobody knows the answer.
I might get really daring if I can find my FSM, and see if it is mentioned in there.

__________________

Gone to the dark side

- Jeff

You have checked the block sensor? Easiest is to unplug it and see if the light is on the same amount of time. As you are aware the sensor shortens the time constant of the relay if the engine is warm. First I might disconnect it and check for a difference.
If suspicious would remove the sensor, check resistance cold and put it in a pan. Heat the water and check for the new resistance. Unfortunatly I do not know it's range but there should be a pronounced swing in output resistance.
I do not know how sophisticated your glow relay is. Might just have the resistance of the block sensor placed across or in series with a resistor in the relay that controls the time constant.
Or is it the one that has no block sensor and relies on information from the number one glow plug? It gets a little more complex then. Rather than tweeking that adjustment you might consider checking the internal resistors for their values as indicated on the colored bands or numerical indications if they are all small wire wound power type resistors.
This depends on how much electrical or electronic experience you have to read them properly.
Consider this. You have two glow relays. If you establish your spare relay works much better. Then open the two of them up if possible and compare the resistor values from one to another. Anything different correct it on your original relay.

My '87 is outside and I'm afraid of the dark but I checked the '85 and the '96 in the garage. I don't see anything on either pre-glow relay that looks like "an adjustment with a lock-nut" except for the main power cable terminal, which is a large brass stud with a nut and a couple of washers. The stud has a cross slot cut in the end and might look like an adjustment screw if the cable were removed. Can you post a photo of yours?

Jeremy

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"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

I think we have a winner (embarrassed), I'll bet that Jeremy is correct about the stud.
Damn, thought I would be adjusting something.

__________________

Gone to the dark side

- Jeff

I vaguely recollect a thread discussing the fact that some glow plugs systems sense the temperature at the engine and other systems sense the temperature in the relay itself. Does anyone else recall that? I think Brian was describing the sensor in the relay version.
If that is true, then it would seem that the temperature sensor in the relay should be replaceable rather than replacing the whole relay.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

All I know is, on my car, the colder the engine, the longer the GP light stays on.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

I believe that the '87 603/300D uses temperature of the relay/inner fender, not of the coolant, that came later.

__________________

Gone to the dark side

- Jeff

According to the W124 FSM (CD-ROM version), as of May 1987, the temp sensor was inside the pre-glow relay.

As of May 1990, a coolant temp sensor was added to the circuit. The new sensor is in addition to the coolant temp gauge sensor. The circuit diagram doesn't explicitly say the new sensor is in the water jacket but I'll bet it is.

If it is possible to open up a pre-glow relay without wrecking it, a savvy technician could figure out which component is the temperature sensor and which component sets the time delay -- and change it.

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