New glow plug relay is not cool! Battery dies on short drives.
 

I have searched the forum for my problem but I can't find anyone with quite the same issue. Lot's of folks with non working glow systems or glow systems that never turn off. Not quite my problem.

Car: 1983 300SD 240k, runs smoooooth and awesome!

I replaced a bad glow plug relay box. It works great. Glow light on the dash cycles on, then off and the engine starts very nicely. Trouble is, the glow plugs do not shut off for 3 minutes, no matter what. I have read that the new relays have this 3 minute shutoff time as a new and improved built-in feature(do not want). I have recently moved within 4 city blocks of where I work. So the time it takes me to start the car, drive to work and shut it off, the glow plugs will have just turned off and the battery never gets an opportunity to recover since the alternator is giving all it's 55 little amps to the glow plugs. Doing this short trip a few times, the battery finally can't keep up anymore and I get stuck. If I drive longer distances I don't have this problem.

Also, if I let the car warm up all the way, turn off the ignition and then turn it back on immediately, the glow plugs will stay on for a full three minutes again. Heck, in this Texas heat, the glow plugs are not even needed when restarting after it's been started once that day.

I never had this trouble with my old relay because once the car was started the relay turned off and the charging system was happy.

Is there any part of the glow system that should detect the engine temp and shutoff the relay? Perhaps mine is malfunctioning? If not, is there a way I could install a manual shutoff switch on my dash that I could just turn the relay off after I start up? I want this relay to function as my old one did before it decided to depart this world.

Thanks much for any ideas!

Temperature sensor controls the length of time the glow light stays lit, it doesn't effect the timer in the relay which is set permanently to a fixed number of seconds.

Yes, you could turn the whole glow system on/off by switching the main line to the glow relay. However, it carries a lot of current so you'll probably need to use a relay under the hood, triggered with a switch on the dash.

That usually low cost fender mounted ford starter relay is up to this service I believe.

There's a wire from the key switch start position to the glow relay to cut the relay when the starter motor turns. Is that wire sending the right signal to the glow relay? In my car it's a purple wire.

Sixto
87 300D

My memory is sketchy, but I think we had a thread on this topic a few months ago. On the 123's I think the glow plugs continues glowing until the timer shuts it off.

In the original configuration, releasing the ignition switch from the start position should end the cycle. My guess is that the OP purchased one of the aftermarket Bosch "afterglow" timers, which is designed to operate the glow plugs for about three minutes following start.

The afterglow relay, however, doesn't run for three minutes if there is no start attempt. In all probablity, blocking the "start" signal would substantially shorten the cycle.

Yep, my memory was sketchy. The debate I was thinking about concerned the issue of whether the glow cycle ended upon engaging the starter or upon releasing the key from the start position.

Yes that is true. I did in fact buy the Bosch relay. If there was a choice of relays that operate differently, I did not know it. I purchased the only available relay I could source locally. And when it comes to parts like that I only buy new.

I never timed the relay to see how long it would glow the plugs if I don't start the engine. I know it does take three minutes after start. Would it be hard to block the start signal? Is that a simple disconnect or is there a rewire in order? And would blocking the start signal mean the plugs would be glowing while I'm cranking on the starter? How negatively would that effect my electrical system?

Thanks for the replies!

It could be that the Relay is defective. I would take it back.

Also when I tested a single Glow Plug connected to an automotive dash type Amp Meter connected to a batter; it pegged the meter at 60 amps (as hig as the meter would go) and as it got yellow read went down to about 16 amps.
So you will not be pulling 80 amps for 3 minutes on your way to work.

Well, I have 5 glow plugs. If each were pulling 16 amps, thats 80 all together. Not to mention the rest of the wiring and plugs and such the electricity must flow through under normal operation. But I'm sure all together I'm not getting quite an 80 amp draw as the fuse on the relay is 80 amps and it has never popped. I do however believe it's pulling at least 55 amps because the battery very slowly drains while the engine is running and the glow plugs are glowing. After the plugs turn off I jump back up to about 13 volts and the battery once again charges up and gives me a very nice crank. No drag at all. So I know it's a good battery. I don't know FOR SURE that the alternator is putting out 55 amps. It's about 6 months old. Was tested at an alternator repair shop (not Autozone god forbid) and they told me it was working just fine.

So is the 3 minute afterglow a correctly working Bosch relay? Is there not a temp sensor or something that tells it to turn off when the engine is warm enough? If not, I think I will need to install some sort of switch to manually control the plug.

Sixto, does that purple wire from the ignition send a volt signal to the relay to shut it off? How does it work?

All this trouble because I live so close to work!

Does the replacement relay have a 4-pin or 5-pin small connector? Afterglow relays have 5 pins.

Sixto
87 300D

The afterglow relays are supposed to use a temperature sensor (in the water jacket) to determine how long to stay on after the engine starts. If the engine is cold, the glow plugs will stay on for up to X minutes depending on which version of the relay. If the engine is warm (~50C or so) then the relay should turn off almost immediately after the engine starts. However, a 617 engine may not have the sensor that the afterglow relay needs, since the afterglow relay was designed for later model diesels (60x series). That may be why the relay is staying on.

The relay small connector pin outs are:

1) red/black +12V with key in run = trigger to start glow
2) violet +12V with key in start = trigger to end glow
3) blue/white +12V to dash glow indicator
4) brown ground

There will be a fifth pin for the temp senor if it's an afterglow relay.

Sixto
87 300D

I think I have the 4 pin small connector but will have to look to be sure. Thanks for the plug specs, huge help! I've not been able to find that anywhere! I'll run some tests today to see if I can figure out a way with the violet wire to control the timing myself. At the moment I'm thinking I would like to install a simple push button that allows the system to work as normal but also sends a +12v signal if depressed. I'll play with it today and see if that will work.

If it turns out I have the 5 pin small plug I'll look into replacing the sensor.

Thanks Sixto!

I have a 3 minute relay too. What I did to get more amps in the battery was first make sure regulator on alternator is good.Second Mercedes batteries have a poor ground.I added heavy ground wire from battery to engine block.My charging after starting is 15.5 volts,then drops to 14.

The plugs are normally glowing while cranking. (If that were not the case, these engines would not start in cold conditions. Anyone who doesn't believe that is invited to attempt a cold weather start immediately after the relay times out.) I suspect that disconnecting the purple wire will prevent the timer from going into the afterglow mode, meaning that the relay will open much sooner than the three minute afterglow period.

I have the Bosch afterglow relay in my '82 300D. If there is no start attempt, the relay opens in under a minute. Disconecting the purple wire should prevent the timer from "knowing" that a start attempt occurred.

While I agree with the glow while cranking, many times the 603 would exhaust its full glow cycle in colder ambients and immediately start upon turning the key.

The glow plugs do not need to be energized to effect a start.......however, some heat is required in the prechamber area.

With regard to the OP, it's agreed that he has procured the wrong relay for that vehicle and must return it for the OEM product.

You are attempting to apply 60x theory to an aftermarket 617 part. The later models had the temp sensor in the timer. It used ambient air temp, not engine temp, to determine the duration of the preglow lamp illumination. The Bosch afterglow relay in question has no provision for monitoring engine temp.

How did you come to that conclusion? The Bosch afterglow relay is specified for both the 616 and 617 engines. (It is packaged with 4 glow plugs!!!) I have one in my '82 300D and am quite happy with it. And a number of other forum participants have reported the same. No way is it the wrong part. It might, however, not be a good choice for someone who makes extremely short trips. But, neither would a diesel be a good choice.

I consider it the wrong part for him...........and, I'm also curious as to why any of you fellows need it in warmer ambients? This one has no issues until it gets quite cold.

I've owned my car for about 5 years now and the most annoying part of the charging system is that when everything is tested and known to be good I've never gotten more than about 13.2v from it. I would feel so much better with about 14.1v... 15.5v seems a little high, did you have to tweek your voltage regulator to get that much? Never the less, I think I will try adding a direct ground to see if I get a charging jump.

Thanks for the idea!

Turn on the headlights and the blower and as many interior lights as you can.

Start the engine and run it up to at least 1500 rpm and hold it there.

Now check the voltage...........see if you get close to 14V.

The part I bought is in fact the Bosch kit that comes with 4 plugs, and then you buy an extra plug to complete the kit. It is listed for my car on all the best and well know parts sites and is considered an "upgrade" from OEM. Now, I'm no expert on how the relay is supposed to act when the key is turned and all that. All I know is that after I start my car, no matter the temp outside or if I just shut it down and re-start, the plugs will glow for three minutes.

I just checked the relay and it does in fact have only 4 pins on the small connector. So if that means it is not an "afterglow" model, then what does it mean that it does not shut off for three minutes?

I've always known diesels are a poor choice for short distance driving. I used to drive much further every day and I still do plenty of 1500+ mile road trips... YOU CAN'T TAKE MY DIESEL MB FROM ME!!! :)

So is my system working correctly? I just am not supposed to drive such short distances?

Correct. The glow plug system is strongly suggesting that you consider the use of a bicycle.;)

I get 15.5 with glow on,lights,sub and amp,defrost high,it drops too 14 in a few minutes.Add that extra ground,everyone will be happy.
Now a stuck regulator will put out 16 all the time,burnt battery out,lights.
Easy way to check a weak battery,get voltage meter. Touch negative and positive on battery.Have someone start car,if it drops below 10 volts,battery is toast.

So I got my hands on a shinny new digital multimeter so I could get very accurate volt readings to you guys :)

Battery freshly charged from a long drive. Key off I have 12.81 volts. Key on and glows going strong battery drops to 12.32 volts. I start up and the voltage stays about the same. 12.25-12.32 volts, even when I rev it up. I turn all loads on(lights, blower, radio, door open) and my volts drop to 12.13 reved. This is on a freshly charged battery that holds 1100 amp load for 10 seconds no problem. Three minutes running and my glow relay turns off and my voltage jumps up to 13.11 volts reved(12.95 idle, battery still recovering I think). I will drive it for a while then check the charging volts before shutting it down to see what I get on a nicely charged battery.

So as you can see with my loads on test, during my glow cycle, there is not enough juice to maintain my battery. Drive short runs a number of times and thats it, no start is imminent.

I've replaced my alternator three times trying to get more charge current but 13.11 is the best I can get out of any alternator I've ever put on the girl. Do I need to look into the grounding? Or is 13.11 typical for this 83 300sd? Or do I just need to start taking the long way to work ;)

Grounding jumped my charge 1 whole volt.

I think I'll be trying out the grounding idea... my neighborhood is not very bicycle friendly. I'm not sure I'd survive the ride :eek:

It means that certain members are providing you with information that is totally relevant to a vehicle model that you don't have.

Ok, so I have a small connector in my relay which has 4 pins. That means I don't have an "afterglow" relay. I'll take that as a fact. No temperature signal coming from the engine will provide my relay with any information. Got it. I am going to try to get my charging system to pump out another volt but, I think I would also like to, dare I say, rig the relay to function differently from it's manufactured purpose. I want it to shut off the moment after I start my car. Again, I live in Dallas TX. Glowing the plugs for three minutes after start in even the most inclement weather here, in my opinion, is not necessary. In fact, before I replaced my relay, on warm mornings with a engine that cooled over night, it would start right up without any glow. Once the temp gets down in the high 70's, it starts to take a lot more effort to start.

I'm willing to install a toggle or button or cut wires at this point. Just need my system to charge right after starting.

To be clear, my 4-pin description came from the 83-85 ETM section of the W126 FSM on CD which shows 4 pins in use in the glow relay, besides the 5 pins to the glow plugs and big wire from the battery. OP indicates an 83 300SD. I cannot comment on relevance beyond that.

What I would do is disconnect the 4-pin connector and test that +12V comes through pin 1 when the key is in run (preglow) and +12V comes through pin 2 when the key is in start. If your car passes those tests, I'll agree it's a bad relay or wrong relay.

Sixto
87 300D

You did, in fact, purchase the afterglow relay. This relay has no input for coolant temperature and will keep the plugs on for approximately three minutes...........with some slight variation due to ambient temperature.

What you actually wanted was the original, OE glowplug relay that shuts off immediately upon release of the key............the relay that 90% of us are currently using for the 617.

Sixto, I just performed the test you outlined. I get 12+v on pin number one when key in run position. 0 volt on pin 2. I turn key to start while watching the meter and pin 2 gets 12+v until key is released. I also tried turning key to run and not starting it. I did find that the relay turned off in about 30 seconds if key is not turned to start. I like that. If I block the 12+v from the start/violet wire, will the relay always turn off in about 30 seconds?

Before I start cutting into the system, I'm going to start by installing a nice ground strap and see how the charging system keeps up. That may possibly provide enough charge to not worry about the plugs glowing for three minutes... hopefully. If not, I think I may install a small push button over-ride on the dash that can either be depressed(no volts sent down pin 2) or not depressed so the glow relay system operates normally. If that idea sounds bad for any reason do let me know.

I understand some of you are saying I have a faulty relay. But when I look up the part, the description says that the relay will run for up to 3 minutes after start to help smooth things out until warm. This is a new "upgrade" to the part that seems to not be an option. Am I wrong? The fact that my relay stays on for three minutes, like the part description says it will, indicates the relay is functioning correctly... right? I'm just trying to get it clear as to how my new relay is expected to perform.

Thanks for the help!

In my quest to find a relay that functions as OEM I could only find the new version. Where can one find the OE without going to a junkyard?

Thanks Brian!

It's the afterglow relay. You may be correct in that the dealer considers the new part to be an "upgrade" and won't offer the original anymore. That would be unfortunate.

The relay that you purchased is performing correctly as designed for afterglow. However, you'd be much better off with the original relay if it's available.

The old version is available in aftermarket. Call Phil at Fastlane and explain to him what you need...........I'm sure he can get it.

It does appear that Bosch has superseded the old version.

I see. This is all becoming much clearer now. Yes, Bosch is the only brand my local distributor carried. So, afterglow I have. And yes I think you are right Brian, I would be much better off without that feature installed on this car.

Thanks Sixto for the wiring info, very valuable! It's nice to know what the relay is doing with these volt signals. For the moment I think I'll block the 12+v signal from the key start position until I get my hands on an OE relay. I have already installed a volt meter on my lower dash, I hate to keep cluttering up this beautiful interior with unnecessary buttons and gizmo's and meters. No push button for me!

I'll install the ground strap and post back my results. I'm hoping I get at least a little bump in charge current. If I do, I'd think that little bit of info should be broadcast throughout the forum as a must do upgrade!

Thank you everyone!

CD

After reading this entire thread, it seems to me that the real problem is your charging system, not the gp relay.

It is true that there is a fairly large current draw when the glow plugs are first energized, but by design the current draw is greatly reduced when the glow plugs reach their operating temp.

I would agree that cleaning/replacing ground cables would be a good start. You might also check the alternator terminals, a loose or corroded connection could cause problems. What about belt tension?

I would also suggest checking the output directly at the alternator output terminal and comparing with the reading across the battery terminals, you might have a voltage drop there.

Thanks King! When I add the ground strap I'll check the voltage at the alternator. Belts are brand new and tightened to spec. Pulley does not slip. Checked it with a wrench.

Update!
 

Thought I'd give this an update for those of you who participated and followed along. First of all, thank you all for the great advice and info!

So, I grounded the battery from the negative post directly to the engine in different spots. My charging voltage never change/improved with or without the new ground strap. I still get tops 13.2 volts even with the engine reved up. I've had this alternator for about 9 months now and it has always performed this way(just like the two before it). So I'm concluding that I have had the misfortune to have three alternators with lower than OEM output. OR there is just something about my wiring harness that I can't detect that will never allow more current to pass through to the battery. What is OEM anyway? What SHOULD my voltage be on this car? No biggie I guess. As long as I don't install a high powered radio or run my glows all the time, it does keep the battery charged.

As for the glow relay staying on longer than I want. I decided to just interrupt the violet wire from the ignition switch(so easy to do). Now the plugs come on, car starts beautifully, glow ends about 20 seconds later. That works perfect for me. Maybe I'll need to allow the 12v signal to keep the glow plugs on a little longer in the winter time, but everything runs nice and happy with this setup for now.

Thanks again everyone!