PeachParts Mercedes-Benz Forum - Best/Easiest way to test glow plugs

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- - Best/Easiest way to test glow plugs (http://www.peachparts.com/shopforum/showthread.php?t=288970)

Quote:

Originally Posted by layback40 (Post 2830947)

If one GP has failed, the others wont be far off failing as well. Best remove the lot, do a valve adjustment while they are out & replace all the GP's. That way you wont get stuck mid winter having to replace GP's. Keep any old ones that are still glowing properly as spares if you must. :rolleyes:
Just remember its a long time till the warm weather of next summer !!! ;)

well, I'd likely not notice one plug out in starting unless it was VERY cold out, but if several are out causing a difficulty starting, I'd change them all.
if during routine testing, I found a single dead plug, I'd just change it with a spare used one.

Quote:

Originally Posted by funola (Post 2831220)

Glow plug is an electrical device and do not behave the same as a mechanical device in the real world. I'd never replace them as a set. I can remove glow plugs 1 through 4 in less than 2 minutes each in winter time so no big deal.;)

In summer time 1 minute each.;)

yeah, but very few of us have modified the plugs like you have. the best I've done is cut the loop on the ends, so I don't have to take the nuts off to get the wires off, just loosen them enough to release the c shaped end!

I live in Michigan = cold winter.
I demand instant starting at -40° Fahrenheit.
If one glow plug fails, they are all replaced "now".
Good used glow plugs are given to local customers in dire economic circumstances..

I found a cool Volt/OHM/AMP/TEMP/CAPACITANCE meter at radio shack
it seems to work well.
AC/DC clamp on TRUE RMS digital meter.
$59 I tested it on headlights, blower, fogs, glow plugs, it seems to sense all the devices. I'm thinking of testing the amp output of my new alternator!
https://lh3.googleusercontent.com/-f...122_084348.jpg

on a related note...

Why In ALL THAT"S HOLY did MB put the glow plug relay where it is on the 87TD wagon??????

ya can't even get the cover off it without removing the vacuum main line, and standing on your head balanced on the edge of the fender holding a bowl of goldfish on your tounge...

Quote:

Originally Posted by vstech (Post 2832775)

Have you actually verified that it measures DC amps via clamping? What is the Radio Shack stock number?

Quote:

Originally Posted by whunter (Post 2831277)

I'd agree if the glow plugs are 10 years old and used alot. If they are 1 or 2 years old and one burns out, I'd say it's infant mortality/ manufacturing tolerance and a waste of money to replace all of them.

Quote:

Originally Posted by funola (Post 2832785)

Have you actually verified that it measures DC amps via clamping? What is the Radio Shack stock number?

22-172

yup. the clamp has three ranges, 40A 400A and ... 800A... great for measuring CCA on a battery!

Quote:

Originally Posted by vstech (Post 2832796)

22-172

yup. the clamp has three ranges, 40A 400A and ... 800A... great for measuring CCA on a battery!

Good find! Finally an affordable DC amp clamp meter! Have it put it on one glow plug and see what it measures?

Quote:

Originally Posted by vstech (Post 2831224)

......

yeah, but very few of us have modified the plugs like you have. the best I've done is cut the loop on the ends, so I don't have to take the nuts off to get the wires off, just loosen them enough to release the c shaped end!

You're half way there from my mods. To go all the way all you have to do is some soldering of the socket pins onto your cut lugs. You can always go back to using the 8 mm nuts by unsoldering the pins but I can't see any reason to go back. This mod makes a miserable job a breeze.

Just bought one for $25

RadioShack True-RMS Digital Clamp-on AC/DC Multimeter 22-172 | eBay

There's more from the same seller for $33

Quote:

Originally Posted by biopete (Post 2593744)

I think its that time of year. Many threads say pull the glow plugs to test them to see if they are really getting hot. But all that work is not necessary . You just need to check if they are pulling amps. All good plugs I tested pulled 20 amps. If they do, they have to get hot right?

I was clued in on this easy way in a post somewhere on this forum. And my friend even made it simpler. I'll go through the whole glow test procedure for newbies.

First pull the glow plug wire from relay. Relay is black box on drivers side wheel fender under hood. When you turn the key on you should have voltage at those pins on the relay. If you are getting voltage at all the pins on the relay, good. If not, check the metal fuse at top of relay if you have one or you may need a new relay.

Next the book procedure says to check resistance with an ohm meter. However this is not always accurate although most times it will show bad plugs. So if you have only an multi meter without a big ammeter, go ahead and check resistance on pins of plug. Put your ohm meter in each pin in the harness plug you unplugged from the relay. Resistance Should be around .6 - .8 ohms , no more than 1.2 or 1.6 or whatever the manual says. My experience is a blown one will be infinite or way above 2 ohms. But regardless, this test is not always one hundred percent accurate so go on to the next test. Its better than nothing if all you have is a ohm meter.

Next *Instead of pulling glow plugs and watching them get hot* , put a jumper wire from battery and touch it to each pin on plug. See if you get a good spark. If it does, its drawing current good and hard which means it should get hot. That's my friend's dead simple way to test glow plugs. He's an electrical engineer. You can also use a test light. If it lights, the plug is drawing current.

If you want to get fancy , buy a cheap ammeter that measures 25 amps at least. I got a meter that is for dash mounting at Harbor Freight for like $5.00 or something. I put a long wire with clip that goes to the battery on the B+ term and a wire on the other term. Strip the end of the other wire and stick it in a glow plug pin on the plug harness. A good glow plug draws 20 to 25 amps.

Thats it. No need to pull glow plugs. My understanding is it is physically impossible for plugs to not get hot if they are drawing the right amount of amps. I'm interested in the physics behind this and why the resistance check is not always accurate. With Ohms law -- V(oltage) = I(amps)R(esistance) or I = V/R means 12.5V / .8 ohms =15.7 amps a glow plug draws. If you measure a glow plugs R and it is within range and you have V , why would you not get Amps?

Assuming that you are working on one of the MB's in your signature, these cars have pin type glow plugs. With these glow plugs it is quite common to get good resistance readings when testing them, but they are nonetheless no longer effective. With these it is best to just change them every few years.

It is not at all uncommone to pull one of these out that has passed the resistance tests only to find a hole burned through the shell.

Quote:

Originally Posted by LarryBible (Post 2832873)

x2

VERY TRUE.
I currently have judging from the starting difficulties, at least 2 bad glow plugs, more likely at least 3 in my 87TD, and the amp meter shows 70+ amps when I turn the key... this leads me to surmise that the plugs are pulling the amps, but not heating.
so... I'll be pulling the intake off my 603, and replacing all the plugs.
meh, there was some oil leaking out of the runners anyway, so it's a good thing I need to work on the car.
I've not got anything better to do:rolleyes:

Getting back on topic. Anyone else bought one of those Radio Shack DC amp clamp meters? It's a great deal if it's relatively accurate!

bump for winter testing...

I have a few inductive Amp Meters like in the Pic. In back are 2 different sized Channels one for small wires and the other for Battery Cables.
You simply slide a Wire/Cable in to the Channel and turn on what ever you are testing.

This was done with a dashboard type Automotive Gauge to test a Glow Plug. The Gauge went up to 60 Amps.
When I connected the Wires the Gauge maxed out for 1-2 seconds and as the Glow Plug got hot settled down to an approximate 16 amps.

So test a good plug to get some specs from. After that you can test them on the Engine.

NAPA was selling the small hand held one similar to the pic for about $22; but it is mostly Plastic meaning no Metal Frame on the Lens. It is small enough to fit into your Hand.