glow plugs staying on? - PeachParts Mercedes-Benz Forum

woodrat · #1 07-06-2010, 12:01 AM

The last time I drove the car a couple of days ago, I could hear a little buzz coming from behind the dash when I pulled into the driveway. It stopped when I turned the car off.

Today, I was looking at the prefilter while the car was running, and cleaning off the clear lines to look at them and realized that the glow plugs and the bent wires between them were still very hot, even though the car had been running for minutes. I kept it running for a while, but the wires between the plugs never cooled off, and I could hear the slight buzzing noise behind the dash still, too.

So I drove the Subaru today instead, until I can figure out what is going on. Any ideas? What would cause the glow plugs to still be that hot for that long? The glow plug light goes out when the engine starts.

Diesel911 · #2 07-06-2010, 12:17 AM

If you have to Loop/Filiment type Glow Plugs your Glow Plug Relay is somewhere Behind or below the Instrument Cluster. That could be what is buzzing.

If it turns out to be the relay it may be cheaper to update with the Pencil Glow Plugs kit that comes with a realy as a new relay is around $250.
The other aternative is a used Relay.

Fattyman · #3 07-06-2010, 12:21 AM

Your glow plug relay is stuck on. Your alternator will not be able to keep up and your battery will not charge. You may also burn out the alternator. The relay is located behind the left headlight in the engine compartment (on a W123). Pop it open and unplug the 5 pin harness (on a 300, 4 on a 240). Does the buzzing go away? Do the wires cool off. If you use a voltmeter you will also be able to see the voltage jump up when you pull the plug.

woodrat · #4 07-06-2010, 12:39 AM

I just went out and fooled around with it again. I found no relay behind either headlight, but I still can hear the buzzing behind the instrument cluster after the engine starts, which is a new noise. This time, the light stayed on for a while after the engine started, too.

I need to change out the speedo head anyway, so tomorrow I'll pull the instrument cluster and see if I can find which relay is making that noise. Sounds like I was probably right to park it until I figure it out.

Thanks!

woodrat · #5 07-06-2010, 12:52 AM

I did some more research on this, wondering why I couldn't refit this system to manually control the glow plugs, and I found a kit for changing this to newer style glow plugs, and also manual control.

Has anyone else done this to their 123? Seems like a good idea, is it?

charmalu · #6 07-06-2010, 01:36 AM

here is a thread with the same yr 240D GP problem

1977 240D glow plug timer relay problem

Charlie

psaboic · #7 07-06-2010, 09:25 AM

No reason why you couldn't do a manual switch conversion. Just make sure you use a heavy-duty switch for safety and longevity.

Where in SW Washington State are you? I might be nearby!

micalk · #8 07-06-2010, 10:20 AM

Quote:

Originally Posted by Fattyman

Your glow plug relay is stuck on. Your alternator will not be able to keep up and your battery will not charge. You may also burn out the alternator. The relay is located behind the left headlight in the engine compartment (on a W123). Pop it open and unplug the 5 pin harness (on a 300, 4 on a 240). Does the buzzing go away? Do the wires cool off. If you use a voltmeter you will also be able to see the voltage jump up when you pull the plug.

Quote:

Originally Posted by woodrat

I did some more research on this, wondering why I couldn't refit this system to manually control the glow plugs, and I found a kit for changing this to newer style glow plugs, and also manual control.

Has anyone else done this to their 123? Seems like a good idea, is it?

The manual for your car states that the glow plug timer (GP relay) is under the dash on the driver's side. The plug is probably 8 pins with two heavy wires: +12V source and one wire for the glow plugs. If you unplug it, your gp circuit will be disabled. Try disassembling the timer and figuring out which relay is stuck - looks like there are three of them in there.

[rant] Why would you buy a car whose marque is one of luxury and modify it so that you have to do more stuff to get it down the road? [/rant] Even with a manual system, you are still dependent on relay contacts and other issues such as lack of documentation, unless you find a switch rated at 100 amps. The updated glow plugs are fine and so is the relay. Just make sure your connections are excellent - solder all terminal connections to the extent possible. With these kinds of currents a very tiny resistance can make a big difference.

woodrat · #9 07-06-2010, 11:21 AM

psaboic;

I'm in Skamokawa, WA, 34 river miles from the ocean on the Columbia.

micalk;

well, while I do appreciate the fine manufacture of this car, and the way even it's damaged doors still close nicely after 33 years, I also am not a wealthy man, and if a relay goes irreparably bad, and I cannot find another one at a reasonable price, yes, I would think about modifying the glow plugs to manual control. If manually controlled glow plugs were good enough for the 115 and 110 chassis cars, I think they could be good enough for me.

Also, I would rather replace a $15 Ford starter relay that I can pick up at the NAPA in my nearby podunk hick town than a $175 Mercedes glow plug relay that I have to drive 80 miles to the city to find, or order on the internet somewhere.

That being said, I will see if I can fix the relay that's in there when I take it apart today.

barry123400 · #10 07-06-2010, 11:33 AM

Wait a minute. At least read the voltage on the plug at the top of the chain or use a test light to make sure they are staying on. If they are on that squiggly wire between the plugs would peel your skin off instantly I would think. It should get really hot.

If indeed you require another relay the auto salvage places or members on our used parts for sale section may be an ecomomical solution. Usually the relays go open but as people have mentioned relay contacts etc can weld together.

The relay you are looking for is gotten to by removal of the fibre or carboard panel above your feet and is mounted on one of the arms that support the brake pedal assembly.

micalk · #11 07-06-2010, 11:47 AM

Good enough. I can certainly relate to that ethic. In my defense, though, the question you posed was one of "good idea", not of economics. You stated that you were replacing the GPs with the pencil type kit, so I assumed the new relay came with it and that you were going to modify the system for manual operation. The relay in my 84 300D was original, I believe, and lasted for over 300Kmiles. I was just making the case that modification to eliminate the relay wasn't necessary. My assumptions, obviously, were incorrect.

If you do replace with a switch/relay combo, keep the fuse inline with the GPs. Use minimum 12ga wire for the heavy current portion of the circuit. If you go to the new GP setup use 10 ga wire for the combined current portion, and 14 ga to each individual GP.

woodrat · #12 07-06-2010, 12:37 PM

I'll be getting in there today to pull the relay out and look at it's insides. I have not yet changed to the new glow plugs, but am considering it if my finances allow right now. My first priority is to get the car road worthy again, and if I can do that today by repairing the relay, that's the best outcome for me right now. I don't live near any salvage yards or parts stores that understand foreign car parts at all, so for me, everything comes either from a day trip to the city, or the internet.

Yes, even without throwing the voltmeter on there, I know that they are still on. While I was wiping down the clear fuel lines, my rag brushed up against those wiggly wires and instantly got a hole burned through it, and this is after the engine had been running for 3 or 4 minutes. Five minutes later was no different. I didn't try the peeling skin test, but I'm pretty sure it would have passed that one, too.

As to the new glow plugs, I was looking at a conversion kit from a parts source that is apparently verboten to mention by name here (old posts of mine mentioning this place later had the name censored out with asterisks). They have a kit that is just for switching to the newer plugs and another that also includes the parts for manual conversion, although I could put the manual conversion parts together at NAPA for less money, I think.

thanks, all!

StaggerLee · #13 07-06-2010, 01:38 PM

Hey Woodrat,
I have numerous glow plug relays for your car and you are welcome to one at no charge if that will help.

I'm in Seattle but travel to Portland once a week and am also in Westport quite often.

If you get me the part number, I'll verify that I have what you need and we'll get it you somehow.

Let me know!

Also, if you call Phil at Fastlane I'm sure he can set you up with whatever you need to convert and you'd be supporting this site. That other place is highly over-rated and over priced.

Dan

woodrat · #14 07-06-2010, 02:23 PM

hmph!

Now that I am ready to deal with it, it's not making that noise anymore, in fact, the glow plugs don't seem to be working at all this morning, and I'm at a bit of a loss as to which relay I should be looking at. There is one big aluminum one on the steering column, right under the dash. It has a heavy clicking feel when the key turns on or off. There is one on the firewall behind the instruments, black plastic, but it's German name translates as "interval pulse generator" so that's probably not it. Looks like there's another aluminum one off to the left of that one, too.

FWIW, I've sensed that people here don't like that "other" Mercedes business, but in the past I've had nothing but excellent customer service from them. I know that their "kits" are priced a little high, compared to the parts contained within, but there is a price on convenience, too. And when I've looked up a couple of non-kit parts here and over there, I haven't noticed that the "other" guys are that much higher.

If I go to my usual import parts place in Portland, that usually gets me the best price on most things, but they generally don't ship, so it means a trip to the city.

Thanks for the offer of a relay, Staggerlee, if I can figure out which one it is, I'll let you know.

Thanks again, all!

woodrat · #15 07-06-2010, 02:53 PM

OK, spent a little more time on this with the voltmeter, and it looks like pulling the big aluminum relay offline makes the glow plugs stop. Turns out that they were staying on all the time after all, but the light in the dash was not working, and the buzzing noise was gone, too. FWIW, the glow plugs had been acting kind of iffy for a week or so already, but it always started up in the end.

Staggerlee, the part number is 001 545 2232; let me know what you want for mailing it if you have it and I can send you a money order or paypal and my address.

If I end up changing to the fast, pencil style of glow plug, will I need to find a later model relay, or change the wiring around at all?

thanks!