My glowplug indicator light stopped lighting yesterday, and my car has become more difficult to start when cold over the last few weeks even though we have had some weather in the 50s.

After perusing several of the glow plug threads, downloading the "checking preglow system" http://skinnerbox.steaky.org/Service/W123/w123CD2/Program/Engine/617/15-710.pdf section of the manual and and did all the tests except amps. (my Fluke multimeter only goes to 10 amps and I did not wnat to blow the fuse on it) Everything checked out as good except the glow plugs. I did check the resistance on the glow plugs and the lowest is 3.2 ohms and the highest is 12 ohms. According to the manual anything greater then 1 ohm is no good, so that means that all my glow plugs are bad. When I put the key to the number 2 position the glow plug light does not light up, but I can hear the glowplug relay click.

Now my questions:

1.If the glowplug relay is good and the glowplugs are all bad, will the glowplug indicator light on the dash not light up?

2. Since my car is a 1985, it has the pencil type plugs. I see Fastlane does not sell the relay only, that they sell a kit which includes glowplugs. This is a new and improved version than what came from the factory. If I am able to determine that the relay is good, do I really need a new relay? I am gravitating towards the new relay because it says it can help give less smoke at startups.

3. I read somewhere about "reaming the glowplugs" what is this and is it
necessary?

By the way, I was able to crank up this morning without the glow plugs (it took a few times) It was right at freezing. Does this tell me that I have good compression, because I have never checked it.

__________________
Doug

1987 300TD x 3
2005 E320CDI

Just getting to the top of the new posts so others will read

__________________
Doug

1987 300TD x 3
2005 E320CDI

1. Usually, if two glow plugs are bad, the dash indicator will begin to do strange things. Sometimes it won't light........sometimes it will light after many attempts.

2. The new relay keeps the glow plugs on after startup. Some folks like the fact that the engine will run a bit smoother for the first 30 seconds. But, a properly tuned 617 with good compression doesn't need the "afterglow". The one at the bottom of this post certainly doesn't need it. If the relay is good, I wouldn't spend the cash on a new one.......unless you have too much of it lying around.

3. Carbon can build up around the plug making removal and installation a bit tricky. Reaming the hole removes this accumulated carbon and allows the new plug to seat properly without jamming itself into the old carbon buildup. Some engines have no issues with accumulated carbon........so........the need to use this tool is somewhat variable. Some folks have had success using a drill bit, by hand, to break loose the accumulated carbon.


If it starts at 32°F. without glow plugs, you can be assured that the compression is decent.

Thank you, You are just the one I was hoping would respond. Thanks for the great info. They have the glowplugs in stock at Autozone in Riverhead for $9.99 each. That is the best price I have seen.

Are there ever any Long Island GTG's? I would love a tech session or two. Talking about doing a job is one thing, and seeing someone with experience doing it is much better.

__________________
Doug

1987 300TD x 3
2005 E320CDI

reithoven,

Something sounds suspicious about your GP resistance readings. Did U pull out the glow plug cable from the GP relay?

If U get the same readings with the cable out, I would check with another meter. Its best to measure resistance with one meter lead plugged into the GP cable connector. Make sure U have the meter connected to a good ground.

Extract and insert the other cable connector in the GP relay about ten times. This may get your GP light to work.

P E H

Correct, it will not light if 2 or more are bad.

If the relay works, you do not 'need' a new relay. Some relays offer an 'afterglow' but it is not really needed.

This involves removing carbon build-up from the head, not from the glow plugs themselves. A reaming tool is inserted into the head to remove the carbon.

Yes, if you can start without glow plugs in freezing weather, you probably have good compression.

Bosch or Beru are good, Champion or others are bad...

Exactly what Jim said.


There are certainly enough of us here to do one. I bet we could get at least seven or eight vehicles........maybe when it warms up a bit.

They are Bosch. My wife picked them up already and they are going in tonight. I will report back how it goes.

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Doug

1987 300TD x 3
2005 E320CDI

Yes, I pulled out the GP cable from the relay and tested by touching the valve cover for ground and each pin of the GP plug that goes into the relay. I am sure I got a good ground because it went from infinity right to the value. I know that digital multimeters sometimes are not good for measuring resistance, but I thought that was in the case of capacitors (I am getting in over my head)
The plugs that go into the GP relay looked fairly clean, but I will check them for oxidation.

__________________
Doug

1987 300TD x 3
2005 E320CDI

Use only German glow plugs bosch or beru. Most of the parts store brands are pure junk and they wont last.

You dont need the afterglow relay if your car is in proper tune.

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

They are Bosch and they are made in France and the local Auto Zone had the in stock for $9.99 each plus tax. The choices for parts stores are quite limited on the East End of Long Island so I felt quite fortunate that they had them in stock.

__________________
Doug

1987 300TD x 3
2005 E320CDI

They'll be fine.

Bosch and Beru might be made in France, but, AFAIK, they still perform as if they were German.

Now........it's a beautiful day........get to work.

Oh........and another thing........make your life easier and take the hard lines off. Just be careful when putting them back on...........make sure you start all the nuts by hand........if they fight you because they are not aligned with the injector.........muscle them into position by bending the line back into place.

reithoven,

I don't know where U get the idea that digital meters are NG for measuring resistance. I'm convinced they are the most accurate.

Get a new GP and measure its resistance out of the engine. It should be 0.8 + or - 0.2 ohm. U should always carry a spare, anyway.

P E H

I said measuring resistance in capacitors, like a motor starting capacitor, but I said I was getting in over my head. I will measure one of the new GPs with my meter and let you know.

__________________
Doug

1987 300TD x 3
2005 E320CDI