I want test the glow plugs I just took out of the car to see if they get red hot and if I should keep them around for spares. They look pretty new. I'm real dumb with electricity but am eager to learn as it seems real fun.

Ok. 1st do resistence check. -- put plug in vice, clamped at the only good spot , the place you put the wrench to turn it. I put one needle of an ohm meter to the tip where the nut threads on and the other to the vice. It reads .5. Good plug maybe if I did that part right.

Now, I want to see if it gets red hot. I'd like verification from someone that my circuit is correct as the first one did not light up and I do not want to destroy potentially good plugs. Here is a pic of my circuit with a battery charger as the power source . The first time I did it I set the charger to 50Amp/Start mode.

http://www.peachparts.com/shopforum/attachments/diesel-discussion/30262d1135051285-hhow-do-i-make-glow-plug-test-circuit-glow_plug_test_circ.jpg

Will this work?

Thanks.,

Attached Thumbnails

 

That should work, as long as that red charger clip does not touch the vise and short out your battery charger. I test my glow plugs on the car's battery. You just need a 10" jumper test lead clipped to the the glow plug's threaded terminal. Hold the glow plug body with a pair of pliers against one battery post, and touch the jumper's lead to the other battery post. If they are good, they will heat up red very quickly

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'84 300D ~90k
'82 300SD ~171k
'82 240D ~175k
'96 Ram 2500 with 12V Cummins & 5 speed ~130k

Thank you. You are a big help. I like the battery method too and was confused about that too and you cleared that up. Thank you.

Question, how will the red cilp touching the vise (sp good ) short the battery charger? Do you mean short as in internal and damaging or just short like touching the two ends together to see sparks ? Or is that damaging ? I was wondering what would happen if the red touched the vise and almost asked . I thought that it may be just like touching the two ends together.

I will use a jumper wire with a small clip at any rate . Thanks again.

And all the glow plugs I just replaced were good. The bosch ones I took out heated up as fast or faster than a brand new AC Delco one I had around (the only one I bought in an emergency one time ).

My method isn't as fancy, or safe. I simply use my jumper cables from the car's battery. I clamp the threaded portion of the GP in the negative cable and touch the positive cable to the GP contact. I do this some distance from the battery to avoid arcs near the battery. Try (really hard) not to short out the cables or to touch the hot GPs.

If you have your battery charger set for 50 amps, touching the two leads together is not healthy for the charger. It may have a protective fuse or circuit breaker inside if it was well made. The vise would just complete the circuit if the red charger clip touched the vise while the black clip was clamped to it

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'84 300D ~90k
'82 300SD ~171k
'82 240D ~175k
'96 Ram 2500 with 12V Cummins & 5 speed ~130k

great idea. Simple, yet complete. This gives me another thought. Try doing this with engine off and headlights on. The headlights should bring the voltage down just a bit, slightly safer for the glowplugs (which are designed to operate on 11V)

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

If you short your chargers leads while in most any mode, you will blow the diode s...they usually have no protection and are way undersized for seeing too much current.

Would essentially make the charger worthless. I've picked up quite a few in this condition and put new heavier diodes in

Your test curcuit would work although I would be weary of the voltage coming out of the charger being too high for the plug. Usually chargers put out 14.8-15volts to charge a battery to 13.8. So your glow plug is used to seeing 11.5 or so volts (at the end of the wire) and you are feeding it with much higher.

If you keep the duration short and don't let the plug get much more than just barely red (I would say 1/2-1second) then you should be able to test without frying the plugs.

Just don't leave them on too long

Pete,

Turn the GP in the vice jaws 1600 mills, 100 grads or 90 degrees so the heater element is between the vice jaws and the terminal is protruding beyond the vice jaws. That way you will eliminate the possibility of shorting the battery charger and damaging it.

ALso, I'm not sure of the connection to the vice from the picture. The correct way would to to connect the battery clip directly to the vise and not to the swivel handle as it appears in the picture.

You should also check the voltage you are applying to the GP. Battery charger voltage must be higher than battery voltage for the charger to charge the battery. You could damage a GP if you leave them connected too long at a higher voltage than they are rated for.

BTW, if the engine starts easily, replacing the GP is a waste of time and money. Remember, once the engine starts to GP are shut off and have no effect on the engine.

P E H

Get a 30A in-line fuse, the kind with wire leads. Clamp one end in your POS (+) alligator jaws and touch the other to the GP tip.

A 'good' GP will not blow a 30A fuse, but if you accidently touch the vice, ground, etc, the fuse will blow and not the charger, battery or alternator.

Oh, and have spare fuses on hand.

Dohh. I forgot about the 11V rating. I was noticing that a day ago. Too much learning in too little time. Its like being back in college. Oh well. I did not leave them on too long I hope. I guess I can test them again with proper voltage before i put them in in a few years. I'm curious to know how a glow plug works internally ie -- what happens whed you "fry" it with too much voltage ?? does the insulator melt and cause it to short out ?? Does the heating element burn out?? What is the heating element made of anyway??
There is too much I do not know to be doing this stuff

The circuit worked. I guess the shiny pivot locking device was sufficiently connected to the blue vise jaws.

P E H, did I give you the impression the car starts easy ??? The car only starts easy when it is above 40F. That and the fact that I just got the car and did not know when they were replaced last is why I replaced tem.

biopete,

Does your car start any easier with the new GP installed?

If you test a GP with too much voltage, you will over heat the element and it might melt and burn out, or get the insulation so hot it fails and causes the element to short and burn out.

I don't know the composition of the insulator or heater element. I don't consider that pertinent information that has to be known in order to service and test the GP.

I don't know when my GP were replaced either but I'm not about to replace them. When one burns out I do a resistance test on all of them to find the bad one and if the others all read 0.5 to 1.0 ohm I consider them good and I only replace the bad one. I always carry a spare, though.

P E H

Nope. Car wont start in cold still. I was sure the reaming would fix it. I'v read a few posts where the resistence test passes but plugs were not heating up well. And an inductive ammeter is the only sure test aside from watching them heat.

I've replaced the glow plugs, reamed the holes (best I could with a drill bit), adjusted the valves when engine was cold at 45-50F , Pulled an injector to see plug heat up in the car, verified the relay works well , changed all fuel filters, filled up with fuel with shots of antigel and diesel911 in case water condensed while car sat in cold with low fuel in tank.

The car fires right up after it has started once or when it is above 40F. It just takes about 15 - 30 minutes of cranking when it is just a little cold. I just got the car so should do a compression check and start of delivery and injection timing next i guess. And maybe find that thread about cleaning the pre combustion chambers good. Could poor compression or start of delivery or fuel injecton timing make such a big differenc in cold starting ?? The car seems to run well and has normal power from what people have told me. There was oil in the injector hole. Is that a good clue ??

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

To lean how to test the glow plug look at this pictorial

http://dieselgiant.com/glowplugrepair.htm

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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

biopete,

High compression is very important to get a Diesel started. The temperature of the air in the prechamber is proportional to the compression, higher compression equals higher temperature. You need the temperature in the prechamber to be above the ignition point of the Diesel fuel or the engine won't start.

I had a 220D that I fried the rings by overheating it. It wouldn't start when cold, even in the summer, unless the block heater was on for along time. If I was at a location where electricity wasn't available for the block heater, I had to park it on a hill to roll start it. Luckily it had an manual transmission. When I was in Nawlins, I had to park in a high rise garage so I could roll it down the ramp.

After the engine started it ran as good as it ever did. So good running after the engine is hot is not a sign that the compression is good.

P E H