three hours of dicking around with two glow plug relays. . . . (we have 4 83, 300d's) from two cars. . . good car quite glowing last week making it a bit of a challenge to start up nere in the frozen north. took the first one apart and skuffed, polished and buffed the contacts. . . . super, tested the terminals, voltage was right there. . . .

NO GLOW.........................................................

what the heck is going on.

cleaned and buffed the second relay, put it on the car, checked the voltage at the posts, 12+, great. . . . . .

NO GLOW ........................................................

ok, this is crazy. checked the voltage at the tips of the glow plugs, just a tad under 12 volts, well, we had a poor ground on the meter probe but still, should work.

this cannot possibly be the glow plugs. . . . . not all 5 of them, that would not hardly be possible. . . . not all five at once. . . . oh well, pull them and lets check them with the meter. . . . . i do have a few extra from a couple parts cars, hell, just put them in and we'll try it. . . . . . . .

started right up.

now what is the chance of all 5 plugs going out at once ? or why did it appear that they were ? the ohm reading was the same on all 5 of the bad ones. . . . i don't remember what it was but they were all the same.

these dang little habit forming diesels are loaded with gremlins. . . . .

another lesson learned on a beautiful sunny afternoon. at least it was not raining or snowing. . . .

davidh

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david h
83 300D Alabama Beauty (Son's)
83 300D West Coast Rust Free that been abused

Chances of all 5 going bad are increased if your relay is failing in the 'on' position.

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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

That makes sense. I'm sure that can happen since it's a relay. A relay can stick in the on position.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

An additional test would be to connect each glow plug (removed from the engine) separately to a healthy 12 Volt battery with heavy wires (jumper cables work well) and see if they actually glow (the tip should glow cherry red).

What kind of "far n.w. Wisconsin?"

Jeremy
ex-Superior

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Whether Intended or from a locked down GP relay...
The "After Glow Light" modification would alert you to Relay engagement.

Thanks to Jeremy5848:
http://www.peachparts.com/shopforum/showthread.php?t=236848

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'84 300SD sold
124.128

beautiful sunny downtown MAPLE home of the n.w.tigers

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david h
83 300D Alabama Beauty (Son's)
83 300D West Coast Rust Free that been abused

Not necessarily. Voltage doesn't make things work, current does. If you can put an ammeter in series with the plugs you'll see lots of current if they're working correctly. If your glow plugs have a high resistance or an open you'll see very little current, but you'll still see 12V. If you don't have an ammeter you MUST measure resistance in addition to voltage to get an accurate idea if your circuit is sound. Probably see a bit less than 12V at the tips as well since even a tenth of an ohm will drop 2 volts at 20 amps. In any circuit that draws this kind of current (electric heater, glow plug, motor, etc.) you need good clean connections and relay contacts.

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mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)