I have a 1984 Mercedes 300D and was having trouble with rough starts even at warmer temperatures (40F) after a cool night. I made it through the winter being able to start the car and began to have problems a couple of weeks ago.

I was able to replace glow plugs 2 and 3 last weekend but was unable to unseize the rest of the plugs and was going to get back to it this weekend.

Now when I go to start the car I notice that the back of glow plug #1 lights up like a candle. No wires are touching the engine and everything looks connected correctly. It did burn out the fuse in the relay the first time it happened before I noticed.

I need to get the car to the garage. What are my options? Can I disconnect the wire and tape it up and try to get the car to start that way? Has anyone had a glow plug do this before? I assume that it means that it failed.

Thank you - apologies if this has been brought up before it's difficult to find this particular subject in a post from searching.

- C. Landry

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1987 420 SEL

Since you have parallel glow plugs then other plugs will work if you disconnect just one

No harm removing and taping up the wire.If it will start depends. I am not sure if heating up the engine to operating temperature or not will help with the glow plus removal.

617 doesn't have a problem with seizing plugs so don't scare him

There is a clamp where the Glow Plug Wires are bunched together. When the rubber on the clamp falls apart the metal of the clamp can rub through the wire insulation causing a short.

Use PB Blaster, Kroil or some other penetrating oil on the threads. Spray it on for several consecutive days.
Run the engine and remove them while the Engine is hot.

I have seen a few threads were a person has had trouble getting one out. They don't usually corroded in but if they did not seal good carbon can get in and fill the cavity.

Then there is the 2 autolite glow plugs that I had the tips swell up on after only 6 months use and I had trouble getting those out. However, on those they turned out till it got to the swollen area.

When the Glow Plug is out use a Glow Plug Reamer (you put grease in the grooves to trap as much carbon as you can) or some alternative method to clean the carbon out of the holes and the Manual has you crank the Engine without the plugs to blow out the carbon.

Use some sort of Never-seeze type compound on the threads when you install them.

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84 300D, 82 Volvo 244Gl Diesel

Never say never. There has been at least 3 threads since 2007 were someone has had at least one stuck Glow Plug on a 617.

They usually don't get corroded in place but it can happen.

If for some reason the Glow Plug did not seal carbon fills in the cavity it can be stuck there.

There is one somewhere in this form where the glow plug body came out but the Tip remained in the cylinder head.

I had an incident were 2 of my Autolite Glow Plugs got swollen tips after 6 months use. They unscrews to the point up to where it hit the swollen tip.

If you can use you block heater use that.

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84 300D, 82 Volvo 244Gl Diesel

This message board is always so reliable.

I taped up the wire on the first glow plug and my car started up immediately. It's warm here today in lovely New Jersey (60F) so that helped but also once I disconnected the wire to the faulty plug my dashboard glow plug light came on which hasn't been working for a few days.

This weekend I'll get the car warm and see if I can get the plug out. I've been hitting it with penetrating oil. Hopefully that will help.

I haven't had the car in my signature since 2006. Probably time to update to reflect my current car.

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1987 420 SEL

All glowplugs can seize and break off. Be realistic.
I had one break off. I removed it the easy way, beat the crap out of the engine on the road until the pin blew itself out of the hole from the pressure.

Sounds like in your case the heating element was was stuck inside of the Engine.

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84 300D, 82 Volvo 244Gl Diesel

Correct. Thats how most glwoplugs break, they seize in place from carbon or overheating swelling. Its rare for one to break off before the threads, especially on a large body plug like used in the 61x.


Copper anti-seize on the body and carbon reaming the bore will prevent nearly all broken plug problems. Long/thin body plugs like the 60x use are much harder to prevent breakage, its good practice to get the engine HOT immediately before attempting to remove them.
I often advise new diesel customers to preventatively remove and anti-seize their glowplugs, most take the advice when they find how much plug extraction costs vs the labor time to prevent it early.
Or, they buy a Cummins and never have to worry about glowplugs!

You can remove the injector hard lines for easier access. Put a box end wrench or 6 point socket on the glow plug and tap the wrench. Don't hit so hard that you break the glow plug. (You're already spraying with some chemical loosener.) As my father in law used to say you'll have "gone from a mess to a helluvamess" if the plug breaks.

Shocking a nut, bolt or glow plug is more likely to loosen it than constant torq.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Yes, do remove the pipes, then after good soaking with p oil work the threads back and forth each time taking it a little further until it comes out. Then always buy Bosch or NGK and they won't swell up on you.

Take your time and you should be fine.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.