Just recently the glow plug indicator on my 1984 300D will illuminate for half a second then turns off. Which make is hard to start, when it does stays on for the duration of the seat belt warning. The car still is hard to start even when it is warm after being driven for 20-30 minutes.

The car now has 82K miles.

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1984 300D, 1972 LT1 Corvette, 2014 Artic White 3LT/Z51 C7, 2013 650i Convertible BMW, 1994 Kawasaki Vulcan, 1992 Yamaha Seca II and 1996 Dodge Ram 2500.

How long is the glow plug relay remaining closed? You should be able to hear it "clunk" when it opens, after the timer runs out and there was no start attempt.

I would pull the GPs and test them sounds like one or two are NG

Your running a 300D on Waste Motor Oil with only 82K miles on it, what a shame

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

So…you would not spend 45 seconds to verify that the timer is operating properly?

The above in red makes it sound like the Glow Plugs are not the only issue.

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84 300D, 82 Volvo 244Gl Diesel

I understand that the light goes out when the circuit estimates that you could try starting, based on the engine temperature. The relay should energize the glow plugs for ~20 sec regardless. Turn the ignition on, but don't crank and you should hear the relay clunk off if you wait, better yet is to measure the voltage at a glow plug with a DMM.

While under the hood, pull the glow plug connector and measure the resistance of each of the 5 pins to ground. Should be real low <10 ohm. Takes 1 min. My son complained of his 84 300D being hard to start. While down there in SoCal, I measured 3 bad glow plugs, replaced them and fired up easy then. I had just verified all good just before he left, so strange 3 failed within a few weeks. I forgot exactly what happens with the light when some are bad. I recall that if 2+ are bad, the light doesn't come on or such, but better to trust a DMM.

On an '84 300D, there is no engine temperature input to the preglow timer.

Should be way less than 10 Ohms. A new glow plug is typically around 0.7 Ohm.

Hmmm....waste motor oil ....what are the odds of excess carbon?

Excess carbon and glow plugs ineffecient heating?

Even checking things with a meter may not disclose this. It may require pulling the glow plugs and reaming to check for excess carbon.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Since you mentioned the Waste Motor Oil.

In more than few threads I posted where The Dole Company had decided to mix there Waste Motor Oil with their Diesel Fuel.
We did work on their Diesel Generators that powered the Refer Units on their Refrigerated Trailers.
What happend is that mix of WMO and Fuel started to plug up their Injectors.
The Injectors in this case had 3 Holes in them and were Similar to the Stanedyne/Roosamaster Pencil type Injectors.
The holes were getting pluged by a white hard crusty material.

I don't know why they decided to mix the WMO with the Diesel Fuel but it sure did not save them Money.

The stock Mercedes Injector Nozzle has a small hole drilled down the center of the Nozzles Pintel.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Thank you everyone, I don't have the meter to test the GP, I did have a set of GP from the 1985 300SD I have access to for spare parts. The one I removed looker realy clean and barely had anykind of damage. I used them to replace the one on my 1984 300D, well all but one, the one close to the firewall was going to be tough to get out. It was in the low 20's in my area so I elected to replace four out of five. The indicator now stays on longer and I can hear the relay kicked of.

The old GP plug had some white power stuff at the end and had some pitting around the last 1/4 inch of the tip. I will take photos to post and get some feedback fromo everhyone. Thank you again.

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1984 300D, 1972 LT1 Corvette, 2014 Artic White 3LT/Z51 C7, 2013 650i Convertible BMW, 1994 Kawasaki Vulcan, 1992 Yamaha Seca II and 1996 Dodge Ram 2500.

A quote from My Post "The holes were getting pluged by a white hard crusty material"

If the Injector spray pattern is bad and to one side it can acctually cause a Hole to be burned through the Prechamber wall; a Glow Plug is easier than the Prechamber wall to burn through.

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84 300D, 82 Volvo 244Gl Diesel