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Old 07-28-2005, 03:30 AM   #1 (permalink)
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Reference Material: Glow Plug system

So, here I am, up kinda late, and feeling like talkin' a bit. It occured to me today, that we have so many new people come through this board everyday, that we take for granted the everyday simple things. Simple things like:
What's a glowplug?

So, for all you who have quietly wondered about this little do-jigger, but fearful of asking, and wondering about this, here you go:

The glowplug is for a lack of a better term, a plug. Not a spark plug, but a pencil shaped rod that has a threaded top to it. This is the golden key to getting your diesel engine to start on mild/cool/cold/down-right-stinkin-cold mornings. If you ever wondered what one looks like, feel free to check out the supporting vendors sites, and see for yourself.

Now, I know it's July and almost August right now, so glow plugs aren't one of those things that you normally would talk about when you can't eat your ice cream fast enough before it melts. But planning ahead and making sure that your glow plugs work properly before that pesky wind chill factor number starts to get on the weather forecast may pay off later.

Anyway, back to our story. . . This plug is the reason for the Wait To Start light on your dash board. This light indicates to you that you have to wait a moment before just starting your engine. Why you ask? It's because that little glow plug has got to . . . glow first.

If you are reading this forum, you may very well be a 6.5 owner, or desiring to be one. These engines are IDI (Indirect Injected) engines. This means that there is a lot more cold metal available at the top of the clyinder than what you would find in a DI (Direct Injected) engine. That extra cold metal provides the stumbling block to getting that wonderful piece of machery out of your driveway and to work/school/kids/the date with your girlfriend . . . during those cold conditions.

Diesel engines fire by heat of compression. Gasoline engines use spark plugs. This means that heat must be present to ignite the fuel. Without that heat, no fire will take place. No fire, no run. No run, no fun. So where does this heat come from on cold mornings? It comes from our little friend, the glow plug. This little marvel actually, you guessed it, glows. When mission control in that computer says "Go" the Wait to Start light goes off, you crank, and away she goes.

Now, with great regularity, the fall comes around every year (just kidding) and all of a sudden people start to say to themselves "My engine has a hard time starting." Now, what some don't realize is that the glow plug system may have been having problems over the warm weather, but it won't become noticed until cool weather is upon us.

So, what do you do? Check out your glow plugs, and see what if they are working properly. There are eight of these, of course. Look for the little wire that plugs in over top of the injector. There is a little flag terminal on top that the wire connects to. Using a digital ohm meter you can verify if you have a working/not working glow plug. One ohm or less is what you are looking for. That is measured with the wire off the glow plug, and tested from the flag terminal to a known good ground source on the engine somewhere. Clean off a spot somewhere to make sure you get an accurate reading. Otherwise, you may condemn a whole bunch of working glowplugs.

What if some fail that test? Well, you have the option of: replacing the bad one/ones, or replace the set. Depending upon the age and your budget would be the determining factor as to what the best thing to do is.

Other determining factors on your glow plug replacement: Depends upon the type of glow plug that you have. Some of these glow plugs of older vintage had a tendancy to swell at the tip. It would then break off inside the clyinder, causing all kinds of problems. For more info on removal, there are threads out there already covering that. So, for some, this is a cheap insurance policy against future engine problems.

So, is that it? Well, not exactly, you also must check to see that voltage is getting to the glow plug. It won't glow if no power is coming to it. Voltage will ONLY be present during the Wait To Start (WTS) peroid. Notice also that the wait to start peroid is much shorter under warmer conditions. Voltage may be checked at the wire coming to the glow plug to a known good engine ground. Clean a spot and make sure it's a good ground. Don't be surprised if you see only 11 volts or maybe even 10. Those plugs put a lot of demand on your batteries, and may very well not show the 12 volts you are expecting. If you see less than 10 volts, you should check your batteries, connections, and charging system. This may also hinder starting.

Where do I get them? Glow plugs are available through the site vendors, and popular auto parts stores.

Any other tips? Yes, check to make sure that your connections are good, clean, and tight on top of your glow plug controller. (Follow the glow plug wires back to the black box) Loose nuts on controller cause bad connections, and possible melt down of your controller connections. For more information on that, see this thread about Turbine Doc's meltdown. Of course I had a meltdown too. So if you want to see that thread, it is here. Must be something about having a meltdown to be a moderator... I don't know.

What would make me suspect a glow plug problem? If you have hard starting when cold, or have a bunch of white smoke on start up. A quick puff may be expected under some conditions. But if you can't see the neighbor's house because of the cloud just produced from your engine, looking at the glow system, is great place to start.

The Service Engine Light (SES) may come on to indicate you have a glow plug system issue too. Check your codes on your computer (see FAQ's - your year will depend upon how you do it).

My Wait to Start Light Does not come on - The wait to start light lights depending upon Engine coolant temperature. If the ECM senses it's warm, shorter glow time. Colder - longer glow time. No WTS light, well that may be engine grounding. The only other time you may not get a WTS light is if you pulled the battery power from ECM. On power up of the ECM, it will not give you any glows. Why? Who knows, it just does that.

Look here-> GM 6.5 Reference Material & FAQ's <-Look here

Diagnostic Links & Common Failures: Turbo System * Lift Pump/OPS * PMD * Stalling

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Last edited by knkreb; 09-26-2007 at 08:01 AM. Reason: Adding stuff
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Old 07-28-2005, 10:02 AM   #2 (permalink)
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Wonderful post, should be a sticky!

3 attaboys for you!


Galatians 4:16
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Old 07-28-2005, 10:04 AM   #3 (permalink)
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Ditto, done

Keep them coming

Adding a little to the thread, Early GM plugs have short service life 11G and later is preferred plug, 60G are latest GM long life offering if I remember correctly, I have run Kennedy quick heats for 2 years successfully now.

These are 6 volt pencil shaped immersion heaters for lack of a better description, zap them with 12 volts and they get red hot so combustion chamber gets warm and toasty on cold mornings, and atomized Diesel mist gets a little more incentive to go bang as piston comes to top of compression stroke, early ones after a time and even later with some age I guess; can swell and left to its own short out and don't glow if lucky, or worst case break off the tip (rare occurance on its own) tips ususlly break when being removed after discoverd not working one.

My opinion and just that, is if you are not sure what you have pull one at earliest convenience drivers side glows are easily accessed and read the numbers on the base of the glow plug, later today I'll shoot a pick of a glow I removed, and an installed one unless someone beats me to it. Glows also IMO should be replaced as a set.
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Old 07-28-2005, 11:07 AM   #4 (permalink)
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WOW knkreb, you were a bit chatty, BUT outstanding topic and thanks

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Old 07-28-2005, 11:07 PM   #5 (permalink)
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These are glow plugs installed and removed, one in my hand is a 11G I pulled for the quick heats, just below threads is where 11G is I'm not sure if you can see it in the close up. Reddish area in the middle is where swelling starts, these have maybe 50K miles ??? glow cycles on them. Green driver handle is pointing to front drivers side glow installed. If pics too fuzzy my apologies, new camera takes too much detail I had to shrink em some to make them fit the attachment protocall.
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Old 10-31-2005, 08:50 PM   #6 (permalink)
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i just changed my glows on my 94 chevy, 192,495 miles.

had a little soot on them, but still working.

new ones work better tho.
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