On one of my MB's (1982 240D) the PO removed the glow plug relay and put a manual solenoid with a toggle switch in its place.
With a relay, according to reports the glow plug resistance controls the amount of time that the plug stays on and controlled by the relay.
Using a manual solenoid, how do you tell when the glow plugs need to be replaced ?

Greg

Glow plug resistance has no relationship to the length of time they are energized with the OE relay. OE relay has a timer. If you're talking pencil plugs you can get a rough guess of the status of a glow plug by measuring its resistance. It should be 1 ohm or less. This is not a definitive test however. With loop plugs you test for continuity through the loop.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

What reports?

Tangofox007, I probably used bad wording. What was meant is this is what I heard from other owners.

Greg

Kerry, yes these are pencil plugs. 82 240D.

Resistance will tell you if they are definitely bad. It will not tell you that they are good. The ONLY way to determine that they are good is to remove & bench test. It will also allow you to de-coke/ream the holes.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Yes, you need to remove and apply 12V to really tell if they are working.

Does MB use a self-regulating glow plug (i.e. can't burn out from energizing them too long)?

Sincerely,

PE

No

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

This one Ohmed out OK but when bench tested was bad.

It gets hottest in the middle when the tip is supposed to be te hottest part.
(This is a Monark Glow Plug.)

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84 300D, 82 Volvo 244Gl Diesel

I've always had problems check the resistance and telling they were bad. This is probably why.

I always pull mine and bench test them. Watch your fingers they get hot.

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I moved the new question to it's own thread!

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Hunter speaking of Glow Plugs dieing due to Carbon insulation
Injectors and Glow Plugs for Dummies - PeachParts Mercedes ShopForum

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84 300D, 82 Volvo 244Gl Diesel

The easiets way is to pull the glow plug harness plug at the relay and apply +12 with an alligator clip directly to each pin of the harness (numbered 1-5). No spark, definitely a bad plug (no current).

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1981 300SD 512k OM603