Author Topic: 300SD Cranks But Won't Start, Spontaneously. Help!  (Read 159 times)

mummyjohn

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300SD Cranks But Won't Start, Spontaneously. Help!
« on: 05 February 2021, 09:14 AM »
1979 300SD, been running and starting fine and dandy for years.  The glowplugs have likely been low- or non-functional for a long time now, as the light comes on only momentarily then goes off.  On colder mornings longer cranking is required to start (since I'm assuming the heat of compression is all that's warming the engine).

This morning I turned the key to the second position (the glow position) and sat in the car for a good minute or two, taking a pause to consider everything I need to pack for a trip tonight.  When I went to start the car, it cranked absolutely fine - strong and consistent as ever - but there is no even vague attempt to ignite.

I tried using the primer pump, I can hear fluid going through it, but still nothing.  This has never happened before and as I said the car's been starting flawlessly, if sans glow, for years now.  I am totally freaked out - what could be the issue everybody?
« Last Edit: 05 February 2021, 09:24 AM by mummyjohn »
1979 300 SD  W116

Squiggle Dog

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Re: 300SD Cranks But Won't Start, Spontaneously. Help!
« Reply #1 on: 05 February 2021, 09:56 AM »
It may be that before only some of the glow plugs were working, and it was enough to start the engine, and now they are all burned out and therefore the engine won't start. Or, it could be that the fuse inside the glow plug module has gone bad--or perhaps the module itself is bad. Either way, I'd suspect the no-start issue has to do with non-operational glow plugs. Even though you live in a warm climate, I think that mid-winter the engine might not be able to start without operational glow plugs.
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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Heated Seats, 350,000+

mummyjohn

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Re: 300SD Cranks But Won't Start, Spontaneously. Help!
« Reply #2 on: 06 February 2021, 11:16 PM »
It may be that before only some of the glow plugs were working, and it was enough to start the engine, and now they are all burned out and therefore the engine won't start.

My contemplations led me there too, and I think leaving it sit for that long glow yesterday morning might've killed whatever one(s) remained.  Each tested at over 35 ohms.

Replaced all five and it started immediately.  Thank god, because I was supposed to visit my girl in San Diego that night...was freaking out when it didn't start in the morning!
1979 300 SD  W116

Squiggle Dog

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Re: 300SD Cranks But Won't Start, Spontaneously. Help!
« Reply #3 on: 07 February 2021, 11:11 AM »
I'm glad new glow plugs solved the problem!
Stop paying for animal cruelty and slaughter. Go vegan! https://challenge22.com/

1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Heated Seats, 350,000+