Author Topic: Glow Plug Woes  (Read 290 times)

avantbenz

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  • 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

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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

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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 Worn out Engine
1979 280SE Euro Spec Import Crank Windows and Cloth Seats, needs head rebuild, and WUR rebuild
1979 300CD


Inventory of w116 Parts
https://www.ebay.com/usr/vintagepartsandstuff/

avantbenz

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Re: Glow Plug Woes
« Reply #3 on: 18 March 2019, 05:40 PM »
Update: After a couple days of spotty connections, she seems to be doing just fine.
Daily Driving 'Patience' ~ 1980 300SD