Author Topic: Glow Plug Woes  (Read 109 times)

avantbenz

  • Enthusiast
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  • Posts: 34
  • W116 Enthusiast
  • Location: Los Angeles, CA
Glow Plug Woes
« on: 04 February 2019, 01:58 PM »
My glow plug lights won't stop blinking and my 1980 300 SD W116 won't start. I feel like I have the Glow Plug blues...should be a song.

Anyway, a few weeks back the lights started to blink and then the car wouldn't start. I didn't know the history on the glow plugs so decided I'd order new ones and hoped that would fix the problem. I cleared the glow plug holes of any excess carbon using a reamer, installed five new Monark glow plugs (used a bit of anti-seize on the threads), and the car still wouldn't start. I replaced the 80 amp strip fuse (although the old one looked fine) and then tested for power using a simple circuit light like this one - https://amzn.to/2SqyiQ9 - and saw that all five plugs were getting power. I didn't check to see how many ohm's though which is probably something I should do.

Anyway, with new plugs AND a new strip fuse the car started up perfectly and I drove her around about 5 times with no issues. Then, last night, I went to start her up and her glow plug light flickered and we're back to square one.

Could it be the relay? That's the only thing left that I could think of. Any other ideas?
Daily Driving 'Patience' ~ 1980 300SD

OLDGOLD

  • Enthusiast
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  • Posts: 26
  • W116 Enthusiast
  • Location: Dallas, TX
Re: Glow Plug Woes
« Reply #1 on: 05 February 2019, 07:35 PM »
Just want to say, I converted to the manual glow system with dash button and absolutely love it.

A new relay is around $800 from the dealer, and a used one will probably be bad as well. Unless you know how to solder capacitors and stuff, going manual is probably your best bet.

I still get the flashing GP light since the coolant gauge wires run through the automatic relay, but I’ve been told there’s a way to wire the GP light to the new switch to stop the flashing. If anyone knows how to do this, please PM me!!!

Diesel 617

  • Classic
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  • Posts: 154
  • 1980 300SD 0M617.950
  • Location: Illinois
Re: Glow Plug Woes
« Reply #2 on: 11 February 2019, 07:22 AM »
From my past experiences you glow plug relay is dead. you could pull the glow plugs out and see if they glow or not. I have had the exact issue you have described multiple times, fortunately I had a supply of old relays, but now I'm on my last one. I was going to look at getting them rebuilt, as the ones I find new for sale online are the later style addition, and I do not know if they work for our w116.

I will email a gentleman who I have had repair and replace electrical comments before for me and see if he can give a estimate on cost to repair these. I will probably have to mail the units to him and it will take about a week or so to hear back from him. In the mean time, your best bet might be to acquire a used unit. They tend to go out between 250-285k miles. SO the less miles on it the better.
1980 300SD
2 OM617.950 complete with transmissions
1980 450SEL Transmission (for sale 150kmi 100$ + freight)

In my imaginary garage
European 1974-76 450SEL 6.9 Green Velour