I've been chasing down an intermittent problem, where I will go for a drive, park the car for an hour or so, and come back to a dead battery. This would happen even on a brand new battery, car garaged all weekend and even hooked up to a Battery Tender, go out to lunch on Monday, and after I've finished the meal, I find the battery is completely dead measuring 8v and cannot crank the engine.

This would occur intermittently, not consistently. It would have to be a heavy current draw to take a brand new battery down to 8 volts no-crank no-start in just one hour.

Finally found the source of the current draw today - glow plug relay. This morning I drove the car only about 1000 feet, so not even enough to warm the engine. Parked, went into a restaurant for lunch, came out to totally dead battery. Popped the hood, engine is cool to the touch, barely lukewarm from such a short drive. But the glow plug relay is scorching hot! Can barely touch it its so hot.

So clearly the relay was stuck on the "on" position while parked. Has anyone ever seen this before? I'm curious at this point, if this is a mechanical fault with the relay physically sticking closed? Or if its an electrical fault with the signal being erroneously sent while parked?

I assume the small gauge two-pin connector is the signal circuit? Maybe I can splice in an LED, so I can see the control signal at a glance?

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1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!

It has happened to others before.



On my year and model there is 2 circuits that activate the GP Relay. The one connected to the Ignition Switch and another connected by way of the starting circuit so that the Glow Plugs are on during starter cranking.

If you get inside of the relay you might be able to tell which set of contacts points is causing the issue.

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84 300D, 82 Volvo 244Gl Diesel

The contacts in the relay have probably welded closed. The relay is a wear item and has a finite life. They either fail in a condition where they don't work, or they fail with the contacts welded shut. Time for a new relay.

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I have a spare, unused relay if you're interested.

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This is not that common, but also not unheard of.

Radio Shack sells an LED / resistor set up for 12VDC that would be perfect for your test. I'd get three, install one for each of the two controls, and third on the power to #1 GP. I'll bet that the issue is the relay (not a false control signal) and a new relay is the answer.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Sounds like concensus is bad relay. I actually have a spare used one from a '97 E300 I owned a while back, so I'll try swapping that in. Thank you for the offer Shertex, I'll get in touch if I end up needing a new one.

I'll also crack the old relay open and see what it looks like inside...

__________________
1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!

Assuming the OP has a W210...

The W210 glow plug relay control is not like the older models. There is a 2 wire connector that does all the control. One wire is the Circuit 50, which is the starter signal. The other is a bidirectional serial data link to the ECU, that actually tells the GP relay what to do, and reports the GP health back to the ECU for display of fault codes.

Hooking up an LED to these lines will not help diagnose the situation.

I agree that the contacts have likely stuck shut and that is causing your constant drain.

__________________
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both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Got the replacement relay swapped in, and popped the old one open to have a look.

Before opening the old one, I noticed that shaking it, it sounded like there was a BB inside rattling around. Whatever was in there must have fallen out as I was popping the casing open, because it's gone now, but I did find one of the links burned out. I suspect the BB in there was a bit of metal, broken / melted from the burned link, and was getting into the relay, completing the circuit and draining the battery. Relay is an electromagnet, so it would attract any nearby bits of loose metal.

The contacts were not stuck shut, which makes sense since the drain problem was intermittent.

__________________
1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!

Check out this thread:
http://www.peachparts.com/shopforum/diesel-discussion/384166-om606-98-99-e300-glow-plug-relay-repair.html

__________________

All Diesel Fleet
1985 R107 300SLD TURBODIESEL
2005 E320 CDI (daily)

LOTS of parts for sale!


EGR block kit
http://www.peachparts.com/shopforum/diesel-discussion/355250-sale-egr-delete-block-off-plate-kit.html

1985 CA emissions 617 owners- You Need This!
Sanden style A/C Compressor Mounting Kit for your 616/ 617 For Sale + Install Inst.

Sanden Instalation Guide (post 11):
http://www.peachparts.com/shopforum/diesel-discussion/367883-sanden-retrofit-installation-guide.html

Interesting, thanks.

Just wanted to follow up as its been 12 days now since replacing the glow plug relay, and not a single dead battery. Problem is resolved!

__________________
1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!

Thanks for the follow-up! I wish all people were as thoughtful. Too many threads get left unresolved.

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