It has been so hot lately, I decided to see how easily my 300D would start without the use of the glow plugs. So one afternoon when it was in the mid nineties, I started it cranking right away without letting the glow plugs run. It ran 8 cycles, that is Ra-da-da-da, Ra-da-da-da . . . fire-up. I am assuming that every Ra or da is one turn of the starter. Maybe not, but it is my unit of measure. Then this morning when it was about 70 or so, it took 16 cycles. They seem to count off in 4s.

I am in Pennsylvania. This heat is nothing compared to Texas. So I am wondering, at 110 degrees or so, which it has been down there for some time, how quickly does your diesel start without using the glow plugs?

And, is there any harm in starting without using the glow plugs, assuming I have a good battery?

Richard

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85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale**
84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 43K
11 Subaru Outback 67K
98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60

Simply avoiding the preglow position on the ignition switch does not disable the glow plugs. Did you take some other action to prevent the plugs from glowing during start?

Nope. I did not disable anything. I just started it cranking, skipping over the pre-glow position. Well, maybe the yellow light came on for a brief second.

Are you saying that the glow plugs are energized while the engine is cranking?

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85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale**
84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 43K
11 Subaru Outback 67K
98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60

My 123 diesel (sold it a year ago) would and my 124 and 210 diesels will start after about 5 seconds of cranking without preglow as long as the temperature in the garage is above 50ºF. As Tango notes, the glow plugs are still being heated (although the starter drags the battery voltage down quite a bit). I'll have to try that test with the preglow relay unplugged.

Jeremy

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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

Yes.

Correct. They remain energized during cranking and stop when the key switch returns to the "Run" position. Later models with afterglow continue glowing even after the engine starts (search "violet wire").

Jeremy

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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

What exactly are you hoping to test or find out with no pre-glow?

Somewhere I learned (vwvortex maybe?) that VW's start a preglow when the driver's door is opened and shut, after the car has been sitting some time. That way impatience gasser types can have more success by just going immediately for the key and cranking.

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Cheers!
Scott McPhee

1987 300D

If you are cranking the Engine and it is not starting unburned Diesel Fuel is getting injected into the Engine. Hardly catastrophic but Diesel Fuel is not the best thing to lubricate your Cylinders.

Or the Diesel Fuel is pooling in the recesses in the top of the Piston Head; I do not see any good coming from that either.

I was surprised to find out the Glow Plugs work when you are cranking the Engine (at leas on my 123 they do). So evidently Mercedes considered having some Glow Plug use important.

If you want to cut out the Glow Plugs completely pull one of the Electrical Connectors; maybe the one that connects it to the Ignition Switch.

For myself; except when I forget I use the Glow Plugs before I start.

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84 300D, 82 Volvo 244Gl Diesel

Agreed; I always glow the '87 even when it's hot and just been run. Glow plugs are a lot cheaper than starters and a lot easier to change.

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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

Same here. It only takes a second or two anyway.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

When my glow plugs stopped working on my '85 300D a couple of summers ago, it would absolutely NOT START even though the air temperature was in the 90's. As soon as I replaced all five glo-plugs, no problem starting.

I don't use the gp's when the engine is up to temp, starts right away.

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83 SD

84 CD

Same thing here, if the engine is restarted warm, no need to let it glow. If you turn the key and the temp gauge goes up, just start it.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

The fuel injected while cranking and not starting is miniscule. Most of it will be blown out the exhaust and very little will get into the crankcase so don't worry about it.

I have my glow plugs under total manual control. I have a toggle switch to turn my glow plugs on (not key switched so I can run my battery down if I leave it on). I have a chime and the glow plug light to warn me against that.

On a cold engine, before I put they key in the ignition, I turn the glow plugs on for less time waiting for the glow plugs to heat up. On a hot engine, I don't need to turn the glow plugs on at all and it will start easily, even 1 hour after shut down on a 90F day.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

A couple of weeks ago my Son in Law Steve called me that the G W Pierce Junk Yard had a Mercedes they thought I might be interested in. Well, it was an 81 300SD and it looked like it had been sitting there for a couple of years. It had NC safety sticker in the windshield. Obviously the battery was stone cold dead, but it looked like brand new from Auto Zone. So I pulled the battery out of the W124, hooked it up in the SD, found me a paper clip and found that little junction box on this car on the lower lip of the passenger inner fender. I jumped the two screws and my little guy Danny pulled back on the stop lever and instantly it fired up. No ignition so no glow plugs, and after sitting in the weeds for over 18 months. The car was driven in to the yard, but the floor was all rusted out. I bought the engine and transmission on the spot and now have them nicely tucked away in my garage.

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Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!