Howdy,
Went for a drive this morning, stopped for a donut, and when I tried to restart my 82 300D (t) the glow light would not come on. So, I quick made sure it wasnt the bulb, then searched some threads. Went out to check the relay, found an inch of water in it! dried it out, put lots of dielctric grease on the fuse screws, tightened everything down real good and tried again. Still no light. But after a few seconds, something clicks inside the car, which I think is the glow click and she starts up fine (though admittadly a smidge slower than usual.)

Heres the question: Does no light indicate that one or two plugs are probably blown, and would it be safe to assume that whatever happened this morning blew out one of them? And since it still clicks, can I not fear replacing the relay?

Thanks,
Paul

I have a hunch that it is due to the relay and not the plugs. I had an intermittant problem and replaced all the plugs only to still have the problem.

Did you check the fuse (80 amp in the relay area) to make sure there is no slight bend in it? That one threw me off for awhile. Doesn't need to be broke, only bent to begin having problems.

Don

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DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
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'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
'82 240D 229k (Matt's - Converted-300DT w/ 4 speed

I've heard of water in the GP relay eroding the traces on the circuit board -- it is possible that the light circuit is bad and the main timer circuit is still working.

Take a look again a the inards of the relay, checking that the traces on the board are all still there. If one is missing or broken, you can repair it with solder or a small bit of copper wire and solder.

The click is the relay opening (will also click when you turn on the key) -- if it starts, the glow plugs are working, just the dash light is not. You can check for voltage at the glow plugs with a multimeter, and also the resistance at the plugs (take the six wire plug off the relay to check resistance).

It is also possible that the resistors in the relay for each of the glowplugs are bad, too, in which case not all the plugs will be drawing current and the dash light won't work.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

If the #1 plug, front of engine is dead you will get no glow light. The other 4 will still glow fine and you will be able to start the car, but it may be a little rough. Even with 2 dead I could start my car, when three went it was almost impossible on a cold (less than 40f) morning. Finding water in the relay circut board is the only difference here. I would try changing the #1 plug, if no change then look for something else. When the glow system on my 67 acted up it was very easy to figure out which plug was bad because it was a series system. The newer systems allow starting with bad plugs where the older system didn't.

Thanks, guys

Diesel Don,
Yeah there is a bend in the fuse; this means its bad? That makes no sense to me, but I'll take your word for it. In the meantime, can I just hotwire it to see if it'll go?

Here's the latest: no more click, no more glow, very poor start with the proverbial puff of white smoke when it finally does. The circuit board was slightly coroded, but the contacts looked ok. There is continuity between the harness and all 5 plugs. Plug 1 looks bad, but I dont know what it should look like. the glass(?) part is all foggy and brown. There is no restistance registering on it or any of the others (though I need a new ohmeter, so that might not be helpful!) If I swith #1 and say, #2, is it possible that it all might work again? (assuming 2 isnt shot too)

OH, one other thing -- when taking out the relay board, I touched a part of the body and made a fun little spark. The main fuse board is still fine, but is there a fuse in line with the big black wire that supplies the power that I may have blown? I'll go check to see if that has power now.

Thanks all,
Paul

Ok, she still has 12v through the wire, AND across the slightly bent fuse.

And I forgot, the battery light stays on now when i pull the key.
Paul

Just an update,
Tracking some other threads, I discovered the alternator was shot. Put a new one in, all is great again. But the light still doesnt come on for the plugs. I think this could be because I changed #5 and #1 to test. I think they all need replacing. Fastlane, here I come.
Anyway, the moral of the story: Check the alternator! I think mine's been dead since I bought it 5 months ago -- put a new battery in it and she's run fine all this time!!!
Paul

The plugs should read .75 to 1.5 ohms each. My fuse has a bend in also. It looks as it were manufactured that way.

I have three bad plugs also. It is difficult to start < 40 deg F. Lots of key cycles and cranking, and LOTS of smoke.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
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'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
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Thanks for the stats.
I jsut ordered a new set of plugs/fuse from Fastlane. I know a bunch of em were bad just from how it used to start. And they are old. This way I can be sure.
Paul

Parallel Glow plugs (GP) very seldom go bad at the same time since they all operate independently. When one goes open (burned out) the indicator inside the car should blink. An easy way to test the plugs it to take them out and connect them to the battery and see how they glow. Compare all five and if one is much slower to glow or does not glow as bright, that is the bad one.

Be careful they get hot. Its best to hold them with two vice grips (VG). Hold the body with one VG and the terminal with the other VG and touch the ends of the VG to the battery terminals.

I have had a GP go bad but I only replace the bad one. The others have gone tens of thousands of miles with no trouble. Remember the GP has no effect on the running of the engine after the first few seconds because they are shut off when the enging starts.

P E H

Just to add a little more info from the service manual (more or less):

For Preglow system eninge 617.950, 1978 to 1980:
"If the glow current circuit is interrupted, e.g. by a defective 80 amps fuse or power relay..., the electronic system receives no current from terminal 30 and the preglow indicator lamp will flash for approx. 30 seconds after the preglow system has been switched on. If one or several pencil element glow plugs or lines are interrupted, the preglow indicator lamp will flash for approx. 30 seconds after starting."

For the system starting 1981 (617 eingine, USA), if there is a problem, the indicatior lamp will not light up when the key is actuated in position "2". The cause can be:
(1) no current to terminal 30.
(2) defective 80 amp fuse.
(3) defective power relay.
(4) one or more (but not all) defective glow plugs or wires to the plugs.

David

In my 4 cyl. I had I think 2 dead plugs, my light wouldn't come on, I could get it to come on by turning it off and on over and over until it lit up, then when the light went out it would start up REALLY hard, I had to keep the accelerator down for 5 seconds or more until it smoothed out and ran normal. It was a real pain to get it started on mornings that were -10C. Before I found out I had dead plugs I was tempted to plug in the block heater.

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Well, I know at least 2 are bad, and the consensus on the other threads seems to be to replace em all and enjoy. I'm guessing they've been in their forever. The previous owner really beat on the thing.
Paul

just replaced all 5 plugs. Then made sure the light in the dash was working( put a new one in). All works like new again!
Thanks for all your help.
Paul