Very true.

Another motivation, though, is to eliminate one of the single points of failure from the system. As you know, with the loop plugs, if one of the loops breaks the entire glow system ceases to function. I had this happen to me about 6 months after buying my car; the #5 glow plug split in two and down she went. Thankfully it was summer in Tucson and the car still started for my wife who was out running errands when it happened, but on a cold day like today it might have left her stranded.

With the pencil plugs now one can fail, or on a warm day perhaps even two can fail, and the car will still start more easily.

Now all that's left in terms of failure points is the 80A fuse, which is much easier to carry spares for and much easier to replace in a parking lot, and of course the glow relay.

Totally fair, but reliability is another question, as noted above. It's absolutely your choice and preference, however.

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1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

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What is it you like better about the loops?

More than a fair point. This is the best reason to upgrade.

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'79 240D

Another thing you must put into searching, is that there are two types of glow plugs.....pencil upgrade and the standard ones that post late 1979 w123s use....while the people who agreed that monark glow plugs are perfectly fine....were they commenting on the upgrade plugs or the standard? I am not starting an argument of which brand to use, use what you like and I will use what I like.....but take your own advice while research and take into account the year if the post plus what type of plug they used.....as the upgrade plug may be assembled in a different factory then the standard.....another interesting factoid, if monark glowplugs are so high and mighty, then why are the Bosch upgrade plugs sold out everywhere?

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Speaking of avoiding points of failure, an old 220D has no glow plug relay and no glow plug fuse, so it is already ahead (?) of some of the more modern cars in avoiding points of failure.

The reason I like the series GPs is that I know right away if one of my GPs has failed. My understanding is that depending on which GP fails with the pencil plugs, your GP light may or may not indicate a failure. I never have to wonder. (keep in mind I live in a mild part of CA, so a complete failure of the GP system is not life threatening)

My 220D has the 5th GP filament on the dash behind the steering wheel. It is a pretty neat way to know how bright the other GPs are glowing. If I went to series plugs, I would need to bypass that indicator. It would be sad to me to lose one of the very unique features of my car.

Also loop GPs typically do not typically need reaming. Also, I have never heard of a loop gp getting stuck in the head.

But at the end of the day, my preference for loop GPs is primarily that I like the quirky aspects of the car.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

^^^^ you make an awesome point on loop glows.....my car had upgraded plugs when I got it so I didn't do the mod.....unfortunately they cut the ground strap but I love the idea that you know right away if your plugs are good or not.....if one breaks, you know it needs replacing....where as a pencil upgrade with not show its self unless removed and tested.....if I ever need new plugs I may contemplating going back to loop and keep a spare or two in the glove box.....quirky features are the best part of these cars....I love my evil servo system because of that....

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A good point, though I doubt that you did what you recommend-and that's what triggered the criticism. I found no bad or good reviews specific to the Monark wide plugs. Did you? I have no firsthand knowledge regarding those plugs. Nobody that I know does, and nobody here, including you, has claimed to have any experience with them. For all I know they could well be crap, but since I don't know, I don't endorse or condemn them. You don't seem to know any more than I do, yet you deliver a blanket condemnation with what appears to be nothing behind it. The OP seems to be the one member that has installed them, so we'll see what he thinks down the road.

As for the current availability of the Bosch plugs, their availablity or lack thereof implies nothing, and what you want to suggest is hardly fact.

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'79 240D

I said what I did mainly to show that a Monark Glow Plug can fail even in Southern California weather.
If one Person cannot use information someone puts out another Person might.
There was no controlled test because I do not have any sort of Laboratory with expensive test instruments.
Story:
I had symptoms of a failed Glow Plug = nailing on what sounded like one Cylinder (notice that this is a subjective as I have not read a really good description of what is Nailing and what is not).
I checked them with an Ohm Meter and they were all the same; none obviously different.

So, I pulled the Glow Plugs and tested them on a Battery and found that one got hottest in the Middle while that other got hot at the Tip.

After the thought to be defective Glow Plug Cooled off enough to be handled I retested it with the Ohm Meter and it failed. Also when I put it on a Battery again it did not get hot at all.

And since then Glow Plug wise I have happily ever after for at least 3 Years now.

What did I learn. Considering price, availability and longevity for My Engine Bosch Glow Plugs Rule the Roost.

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84 300D, 82 Volvo 244Gl Diesel

Diesel 911, You don't need to defend your opinion! I certainly don't feel that your process was flawed, and I wouldn't expect you to have done extensive controlled experimentation just to be able to post your opinion. You conveyed personal experience, as I did, and left it at that. Even though you indicate a bit of a bias, you do have some justification for that bias, and you haven't suggested that using a brand you don't prefer is a mistake. That's pretty well balanced.

The previous owner of my '79 240D managed to squeeze 18 years out of the original glow plugs before he needed to replace them. His second set was still in use when I took possession 10 years later. Were they superior quality? Maybe, but based on that information, it is still not reasonable to conclude that glow plugs should last for 10 or more years. Perhaps the facts that the car had had been driven less than 20K in its first fifteen years, and that the PO always used the block heater, year round, before he started the car every day, greatly extended their life. His experience does not give anyone reason to think that a set of glow plugs should last anywhere near that long. With a good data set, that single experience would be an outlier, and it would be (statistically) meaningless.

Point is, that there is no statistical evidence or results obtained from controlled experimentation to guide us in making this particular choice. I'll leave it at that.

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'79 240D

I actually have firsthand experience with Monark plugs. Hell, the same one's in that "kit" you purchased. I did purchase this kit myself a few months ago. I will give it this; they worked beautifully and made the car so much nicer to start when cold.

HOWEVER, please note the word "worked".

2 failed almost instantly on the 1 month mark. I did a full diagnosis of the GP system and the only plausible cause was a premature failure. I still have the plugs sitting around; they're brittle. Not very good....I'm really lucky they didn't snap on me. I immediately bought some Bosch large-bore plugs from Pelican and they've worked flawlessly for the past few months. And in the much colder weather to boot! I can't imagine those Monarks in weather like this...

TL;DR, These "opinions" against Monarks that people rant about have much credibility to them. The fact is they make a shoddy plug.

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- 1979 W123 240D 4-speed, 390k miles

The plugs in my kit game in Bosch boxes, so unfortunately I'm not a good test case for the "Monark controversy".

We do love our quirks in owning these cars, that is part of the charm. I always liked the super old school glow plug "indicator" that was another glow plug in the dash, talk about a simple and effective engineering solution!

Loving the "quirkiness" of the ACC unit is a bit too far for me though, I think whatever Mercedes executive made the call to replace the best system ever created (the one I had in the 75 300D) with that abomination should be bludgeoned with it.

Right now instead of three 40 second glows and crank crank crank it's one ten second glow and the engine fires as soon as I turn the key. I have a slight miss the first ten seconds or so I still have to rectify, but I will not miss those loops the slightest bit. I'll bet it's the one injector that looks different than the others.

"Three 40 second glows" is a LOT! That must have been on a very very very cold day. That is way outside the recommendations of MB that came with our cars, so I wonder if something else was going on. After I replaced my GPs the first time (as a preventative measure upon obtaining the car), I noticed that the required glow time was much longer. It turns out that there was so much caked on dirt/oil on all the connectors that my "fix" was actually worse than before. I lived with it until the Bosch plugs started suffering premature failure due to my engine running too hot. So I took it all apart again and used sand paper and steel wool to clean everything. I also used antioxident grease on all the connections. This is the grease you are supposed to use for aluminum wiring in homes (kind of the opposite of dielectric grease).

If I didn't know better, it would be easy to conclude that my new Beru plugs work way faster than my old Boschs. But it is just that I got everything cleaned up appropriately. Your experience of going from 3X40 seconds to 10 seconds is remarkable. My w124 probably needs 15 seconds of glow to start without too many misfires. And my w115 probably needs 30 seconds of glowing. These numbers are on a cool San Luis Obispo morning, which is probably 45 deg F. The compression on the w115 is good (400 psi or more), but I haven't checked the w124.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

I just talked to the Bosch folks and was told I would need a new controller for the relay if I installed the 80035 glow plugs in my '78 300CD. Is that why"someone" sells a kit with a remote controller?

The kit is meant to replace the original glow control and relay instead of trying to find rare and expensive original equipment. The pencil style 80035 glow plugs will work just fine with the original relay and timer but you will have to "manually" time the glow your self rather than waiting for the glow light to go off.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

This is correct but I have noticed on my 77 the light seems to function normally. Not sure what the reason is but I'm not complaining.


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