Glow Plug Question

[Jaryd]

After changing out the valve covers and putting everything back together I’m ready to bleed the air out of the lines so I pulled the 7 easiest glow plugs. These have about 16 thousand miles on them.

Do they look good for that amount of mileage? And do they look good enough to keep running them? I don’t see any erosion or anything on them anywhere.

 

[ak diesel driver]

Other than looking for erosion, or physical damage a visual inspection won't tell you much about glow plug health. Those look just like my 3 totally dead ones

 

[Wreckinball67]

You can test them with an OHM meter. Not sure what the resistance should be off the top of my head...should be easy to look up the resistance on the web. Then, look for a variance between the glow plugs. If there is an oddball, replace it. I did this for a Mercedes CDI and found a bad one, which there was a trouble code.

 

[Jaryd]

The truck has never had a problem starting and it’s never been plugged in. Since I had them out I wanted to post the picture and get y’alls opinion on them. I have never had a reason to check them until now since they are already out. I’ll OHM them and see what it comes up with.

 

[MrMarty51]

The Delcos in my 2000 looked like new. It had no starting problems. I dont know the history on tje truck or engine so I replaced them with new. Just didnt want to have to deal with bad GPs down the road.

 

[Jaryd]

This one don’t have starting problems either. I have never really had to mess around with glow plugs in the past so I didn’t know if all other trucks glow plugs with 16 thousand miles or so on them look like that. I didn’t know if you can tell by the plugs if the timing needs to be messed with or not. I have never had my truck hooked up to a scanner to see where the timing is.

 

[Will L.]

No timing erosion there.
if it aint broke, dont fix it

 

[EWC]

Most of them should ohm around .8 or .9 .

 

[Will L.]

To know the correct resistance of a heating element you need to onow the wattage. Then divide the square of the voltage by the wattage.
So 12x12 divided by that particular brand wattage.

Old wellman -now dieselrx- are higher wattage than even the old ac Delco 9g was. Thats why they got hotter, but they also drew way more amps, which broke off more often and burned out relay/ controllers faster because of it.

Then also, (and this part is speculative) the self regulated plugs have a constant draw when cold as when hot. I learned the warm engine changed the resistance of the other plugs. When I switched to self regulated I tested and learned they are a constant draw unit.

Back before working on rigs as a job, I was an electrician and am back in that line of work. In a training class an instructor used 3 water heater elements as part of teaching about resistance and how resistance affects other factors. Contamination or the element itself wearing away changes the resistance and therefore its efficiency (performance).
The more contamination there is = more resistance.
The more worn off the element is = less resistance.
But you can have 10% wear and 10% contamination bringing the resistance to a perfect reading while efficiency is 30% lower than new. Remember the square of the resistance so that amount plus the loss of element material function.

When he taught it I never messed with water heater elements, but brought up the 6.2’glowmplugs and glowplugs. I had a habit of saving my old parts just in case needed. I also used to label which cylinders on glow and spark plugs- something picked up at the dragstrip. He had me bring in parts and we tested all my old and even tested plugs in my engine, then pumled the ones from my engine as he explained meggers and fine resistance into the block farther from the ground cable. I actually learned I had one bad injector and another going bad because of the recorded history how two cylinders were wiping out glowplugs at a faster rate than the other 6.

So when I later worked in the fleet, I argued the point with bosses and thats what started the testing of plugs out of the engine. Thats when we found that good plugs can actually test bad, and bad plugs can actually test good when using the resistance as diagnostics. Btw, using amp will do the same thing, except make false readings worse because of bad grounding at plug, cable, etc. it is good to help learn of grounding issue- but doesn’t prove bad plug. Same reason when you amp test a starter, if it fails you the remove and bench test the starter and redo the amp test and if you variable is more than 1% you are to remove and clean grounds, and test battery cables with a megger. Then there is this fun factor to add in. When we were testing them in the shop one guy randomly grabbed 2 as comparisons right from the box and had a reading one at minimum ohm spec and the next at maximum- it was a hilarious example of mass production at it’s worst. So he checked all 32 new ones we had in the parts room. Thats when we actually bench tested them.
As pointed out by WarWagon, back in the day a cheap but accurate non contact thermal gun was not available. Now they are everywhere- harbor fraud has accurate ones for like a nickle! Why did GM say to use ohms? Because something other than replace with known good was desired.

So in the fleet what did we learn was the best method? When a hard start is noted, waste no time testing something that will give a subjective answer. Quick voltage check if one is getting power shows power good to plug. Then Grab 8 new plugs and swap them in and eliminate down time. Then you can put 4 in a vice easily at same time with a singe jumper lead with a battery jumper box (ground to vice, positive to lead) then the next 4. About 2-3 minute test and you knew which to reuse and what hit the trashcan. Use needle nose to remove connection and let the 4 fall or wear welding glove because they are hot a minute after testing. If you don’t have a vice at home, test one at a time.
Remember the contamination issue? Own a stainless steel wire brush and SAFETY GLASSES? Get it hot, disconnect power and a quick swipe on two sides. Rehook up power and use your temp gun again- ya might be surprised. We learned dont do it while they are energized and full hot because they look like a 4th of July sparkler sometimes depending whats on it, and yall know I am not safety sally over the top- so when I say safety glasses- believe it.

Now, back to the formula of testing plugs-note I didn’t mention what wattage for the formula. Why? Because they are tremendously all over the place. Like saying a light bulb in your house. Old school 60watt, or brighter porch light 100? “3 way” floor lamp bulb or is it fluorescent with newrly no amps and insane high wattage. Different brand glow plugsfor the 6.2/6.5 engine can literally have way more than double the wattage. The factory ac Delco 9g was discontinued so long ago that they reused the partnumber into the duramax. Anyone here think the AC Delco 60G self regulated unit is the same wattage or resistance as the old 9G? Haha. Yet look into the measurements for testing spec. They didn’t bother changing it. Why? Outdated engine that is no longer under warranty so they dont give a rip. On things that did change like fuel composition and had huge effects of wear of the injection system they didn’t make any changes for the consumer- even to the point of the lawsuits over the cp3! What makes anyone think they will spend money to update and outdated spec on an outdated engine not using updated tools- they don’t care. Like how humidity in the tire affects wear by different tire pressure- one question is applied: Do enough fail under warranty that we loose too much money? If the answer is no, let it go.

I have tried to dispell this myth as much as possible. Due the bench testing yourself, just be sure to go through enough sample to be fair- say 50 plugs. I would imagine there is enough folks here that if 10 people tried 50 used plugs, 1 person could say honestly that they think I am wrong because their testing matched simple ohms test by results. I also bet 7 would be able to confirm my test results as accurate without any doubt. It might have been unfair, but after the 3rdguy challenged me on the job, i kept a set of 8 plugs in my parts box at work as demo. I gave them to a guy when I quit wrenching pro, so he could show other doubters on the job and a chance to make back the $20 he lost to me on the promise he would only take the money once to break even.

Please put glow plug ohm test to bed along with rear head cooling loop kits for the sake of 6.5 love (or hate, depending on the day).

 

[MrMarty51]

Now that is some mighty interesting information. I have a set of real nice looking used GPs in my tool box, guess one of these days when I get bored I’ll have to give them a run.
Might just be worth it to test new GPs too. We may never know how many bad ones there are right out of the box unless a person jumps in and tries the test on them too.

 

[Husker6.5]

What is it that @WarWagon always says? Oh yeah, "New doesn't always mean it's good."

 

[JMJNet]

If it does not give you any problem, I would install it back.

 

[Husker6.5]

If it does not give you any problem, I would install it back.

Yup, if it ain't broke, don't fix it!

Those look like they're nearly new! As I was writing this, I grabbed one of the old glow plugs that came out of my Burb that had been fried by the lot boy at the dealership I bought it from in Mooresville, NC, who while trying to start and warm it up on a 35° December morning before I got there (despite my telling them the night before NOT to as I wanted to cold-start it myself) evidently didn't know what the Wait To Start light meant and thought he could just hop in and crank it. Then, after running the batteries down, wheeled out the big dog battery charger and when I pulled up, was trying to start it off of the 500A Jump Start setting - nevermind the warning sticker about trying to start it off of a charger! End result was that he fried out all eight glow plugs by running 15+ volts to them when he turned the key to crank it over on the charger.

These fried plugs of mine look like they're brand new, so looks can be deceiving, as I've seen ones with a grayish ash coating and slight erosion on the tips work perfectly fine, too.

Not sure what these are, NOT GM/ACDelco as there's no 9G, 11G or 60G stamped on them, nor a Bosch logo, just 2757 stamped up one side of the hex.

 

[Jaryd]

There is some good info here. Thanks guys. I had planned on reusing them again unless one of yall seen something that I didn't know about. Hopefully I can have it all back together this weekend and drivable again.