Hi guys, I've been having an issue with my glow plugs.

When I bought the car 2mo ago, the glow plug light was not coming on. I wasn't even sure if the plugs were coming on or if the bulb was burned out. I ended up replacing the older plugs with newer pencil style. I also replaced the wiring, fuse, and fuse box. The glow plug light would still not come on, but I could hear the relay clicking on and off. However, the main wire going to the plugs would only read 12V intermittently.

I would have to turn the ignition 2-4 times for the glow plug relay to click on fully and power the plugs (and read 12V). The glow plug light was still not coming on, but I could tell when the plugs were on as the interior dome light would dim for about 5-10sec, then go brighter. The car would start perfectly.

Thinking that the ignition switch had a loose connection, I replaced it. Apparently the old one was fine as I am still having to turn the key 2-4 times before the interior light dims, letting me know that the glow plugs are being heated. However, each time I turn the key, I can feel the relay (I put my hand on it) clicking even when it's not powering the plugs. The glow plug light still does not come on. I swapped the bulb with the working seatbelt bulb to eliminate the possibility of a burnt out bulb.

This morning, it was about 50 degrees outside. I turned the key 2-4 times and the glow plug light finally came on (for the first time ever), however it was dim. When I started the car, the light became fully bright for .5 - 1 seconds, then turned off. Is there a temperature sensor in the relay? Would it being colder outside have something to do with the light bulb coming on?

At this point, I am thinking that the relay is going bad. But before I spend $250 on replacing it, is there anything else I may need to take a look at? I've replaced all fuses in the box to rule that out.

Temperature outside could be a factor as you mention of course. If you can source a good used relay from a salvage yard or elsewhere is one option.

I am hesitant to mention this but good used relays are going to become scarce to find at some point. So if the relays internal points are still in good shape the day may come where we rebuild/repair the electronic/electrical portions ourselves.

To make sure it is the relay and not some external connection you want to hook up a meter between the relay trigger wire from the ignition and ground. This to make sure youi are getting 12v every time you turn the key to that point. This should be checked at the relay. Also make sure the ground for the relay is good. It sounds like temperature is a factor here so a cold solder joint or connection for example could reflect that.

On some of the Models the original Silver Box type Glow Plug Relay (behind the Instrument Cluster) does not function with the new Type of Glow Plugs.

If the original Glow Plug system had a 50 amp strip Fuse on the Fire Wall or no Fuse at all (inside of the Relay is a Reed Switch that will disconnect when the Switch gets hot) I don't believe it can be used with that Relay.

Repair Links
http://www.peachparts.com/shopforum/diy-links-parts-category/

http://www.peachparts.com/Wikka/DoItYourSelf

__________________
84 300D, 82 Volvo 244Gl Diesel

That would lead me to clean the contacts on the relay itself.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Do you know what each pin is for or what each colored wire is for? The relay has seven pins total. I would like to test to see if I am getting 12V from the cord when I turn the ignition to glow. If I am not, then I can assume that the problem isn't the relay.

I read somewhere that the old relay will work, but can burn out the plugs if the key is left on in the glow position for too long as the old relay doesn't have an automatic shutoff timer.

The old relay with the fuse on the firewall does indeed work with the new plugs. At least, it should. It works on my '79.

The timer may not function as designed with the new plugs, however, as noted. I had read accounts of it before, and experienced it myself on my car. The glow plugs will stay on as long as you leave it in the glow position.

The glow plug light still functions as designed after making the transition, in that it provides an estimate of when the glow plugs have heated the pre-chambers sufficiently for an easy start.

I thing the suggestion is good to clean the contacts on your relay.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

When I left work today, the glow plug light came on after turning the key a few times. However, the glow plug relay is not staying on long enough to smoothly start the car. I'd say it stayed on for 2-4 seconds. When it's 60 degrees out and the engine has been sitting for hours, you'd think it would stay on for at least 5 seconds.

Did the light go out after 2-4 seconds, or did you confirm that the relay turned off after that long? The light turning off doesn't alone mean the relay turned off. The relay should normally stay on until you 1) start the car or 2) the timer (if its working) goes off and that's about 45 seconds.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

Get a real hefty pushbutton switch, momentary contact, mount it on the left side of the dash so you can press it with left hand. Fuse it from the battery, and feed the output to glow plug harness hot side.

Problem solved for life:

Push and hold the button for ten seconds, just count in your head, in the tenth second release the button as you turn the key to "start".

To finish the job, remove glow plug relay and toss.

... never look back.

__________________
Cheers!
Scott McPhee

1987 300D

I can hear the relay clicking off and the light went off. I just went out and tested it and the relay clicked on, then off 2 seconds later, but the light never came on.

For those of you with a working glow plug system with the older style relay, do you mind testing something?

I tested with a multimeter the voltage at different points with the key off and the key on. With the key off, I get a constant 12.6V at #5 (left side, second hole down), but none of the other ports read any voltage. With the key on, I get the same at #5, but also #4.

Could you test the ports and see if you get voltage at the same points?

Listen to Scott....
" for life "...... no more of this kind of aggravating stuff....

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

What kind of switch should I buy? Should I rig up a solenoid like some people do?

I mentioned on the other thread....to clean the ground points on the car....guess this was ignored...

Before running out and buying stuff, clean the ground points and learn how the glows work..

I believe you are having other issues with the car besides the glow plugs. If injection timing is off, clogged fuel filters, leaking fuel lines, bad injectors, bad ground connections, worn starter, tight valves, bad battery cables can all cause issues relating to starting.

The early glow system, relies on temperature switch in the head to tell the relay when to operated and when to not operate. Unlike the later models that have the temperature switch built into the relay under the hood and sense the temperature under the hood. This is why the older w123's glow plugs don't stay or come on as long as the newer models.

The glows don't start the car, they simply heat the prechambers to combust the fuel. The starter builds the compression up in order for the fuel to combust. A good running engine will start with out the help of glow plugs.

Metal expands when it is warm and shrinks when it is cold. Thus there is a bigger gap between the rings and the cylinder walls the colder the engine is. The glows help heat this area to expand the metal...

These cars, take a multitude of things running correctly for easy starting and smooth idle.

__________________

When I pulled the cluster a few days ago, those ground points were cleaned. I also cleaned the battery ground. This is really the only issue I'm having with the car (glow plugs).

The car starts perfectly, when the plugs actually come on. It runs smoothly and quietly. All fluids and filters are only about a month old. When the plugs don't come on, it takes a few seconds of cranking, especially when it's 50 degrees outside (like it is now).

I didn't even think to check the temperature gauge at the engine. I cleaned those contacts too, but it didn't seem to make a difference. Is it the one closest to the radiator or closer to the firewall responsible for glow plugs?

I also noticed that the glow plug light only ever comes on when the engine is cold. When it's warmed up, it never comes on. Below is a video of me attempting to turn the glow plugs on. The car was recently driven, but has been sitting for about 20mins. You can hear the relay clicking off at several points in the video. The engine is still warm, but the relay clicks off WAY too soon (around 23/24sec and again at 29). Notice how the battery light became more bright when the relay turned off?

There is a gremlin somewhere. At this point I'm thinking it's either the relay or the temperature sensor.

http://youtu.be/e9ubysouH3w

Yes,,, the solenoid setup shown lately in several threads is nicely executed..
I see it as a life time fix if properly done... ( soldered crimp on ends to the wires, shrink tubing , etc )...

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html