Most people use Bosch. Beru cost more, harder to find and may be slightly better.

However, this is the Bosch Glow Plugs made in Germany or France. It is possible that the are also made somewhere else now.

If you removed the Fuel Injection Hard Lines you may need to bleed the Air out of them by leaving the Hard Line Nuts Loose at the Injector and cranking until Fuel comes out. Afterwhich tighten them and attempt to start.

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Bosch or Beru others burn out to fast.




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I am changing the glows in the 85 300SD today. I got them all out with just the normal amount of grunting and cussing and they all look brand new.

So I decided to test them with the jumper cable and battery and they all look to be working just like new.

Now I am wondering if I have a bad wire on one of them.

I guess I will put the new ones in and hope for the best.

Any suggestions from the collective wisdom?

what I am now understanding about glow plugs, that even if they light up. They may not be good. They aren't like a light bulb, but more like a resistor. With age and voltage their values drift thus not producing the correct heat. So the only way to test them, is to ohm test them...if the reading isn't to that of a new one...its worn...also I've read that the glow plug relay produces 8-10v mine produces 10v....your battery produces 12-14v thus making the plug brighter and producing more heat....this is why people tell you to run a jumper cable to the plugs to see if that will start the car more voltage equals more heat..

The wires can be tested from the larger of the plugs in your gp relay. Pop it off and there are the termination points for each gp clearly marked on the connector.

To ground, each of them should read less than one ohm. Best scale to read them on is your lowest one.

Well, thanks Jay.

I have them all in and wired now. I am pretty warm now so I'll go out and reinstall the hard lines and see if it fires without too much stumbling.

that's a fast way to test them. BUT I must still emphasizes that you look at the glow plugs as a resistor....if you test them through the wiring harness...all that wire adds resistance....you have to remove them from the circuit to get a proper reading....

I got it all back together now but have not been able to get the air out of the lines and now the battery is down so I am waiting for it to charge for another go later. Unfortunately now its dark but should be able to getrdone by flashlight.

Thanks for all the help.

I don't have an ohmmeter though so perhaps I should break down and buy one.;)

A new glow plug reads 0.7 OHM.
 

I just bought 5 new Bosch. I have a pretty accurate Fluke. Just out of curiosity I measured the new and the old. 4 new were .8 and one was 1.2

The old ones were .4, .8, .6, .8, .2

So can we assume that the .2 one was the bad one or does resistance rise
as the fail, unless the element does burn out like a light bulb resulting in zero
resistance?

I just replaced ALL of mine beause I forgot about testing with a battery, although now I see that just glowing isn't all it needs to do, it needs to glow
in the proper way as well.

Actually the resistance of the copper wire is very close to zero. 3' of 10 gauge wire is .003Ω I doubt if most regular digital VOM's will read finer than .1Ω.

If you are pretty sure you have one out. Just pulling the connector at the harness will get you pretty close.

The box on my new Bosch plug had a pretty good representation of what is going on in the the pencil glow plug. There is a small coil of wire that travels down to the end of the probe. I can imagine it shorting on the inside of the pencil .

Well, after a couple of hours charging the battery it started right up with some wd40 to prime it.

I'd still like to test the old glows though so I guess I will buy an ohmmeter.

The GP resistance is very high/open circuit when it fails. Not zero. GP in general measures at very low resistance, < 2 ohm, are good. I reckon all the old one your replaced are good. When GP glows, the resistance will kind of reaching a steady state and draws about 10 to 12A. Most GP are rated at 120-150W ( battery voltage x current drawn, 12v x 12A = 144W ).

Tom, you can get a good meter at harbor freight for less than $20

We don't have one here. How about Autozoo?