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How do I test my glow plugs??????
- Thread starter wlrdlr49
- Start date
chrisk1500
New Member
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Only way to test 100% is to pull them out and apply 12V to them via a battery. They should glow bright red/orange from the tip to the middle of the plug....
DennisG01
Member
As this site is still relatively new, I don't think you'll find to much if you use the search. As stated above, a sure fire way is to pull them. However, a "quick check" is to hook up a test light from your positive battery post to the spade on the plug terminal (remove the plug wire, first). The light should light up. If it doesn't, the plug is bad. However, if the light does light up, the plug is "probably" good. This really only tells you if you have a completely bad plug, but it is easy. You could also do a resistance check on the plug between the spade and the case. A good plug would read between .6 ohms and 1.2 ohms. NOTE: This in not "K" ohms - we're talking single digits, not 1,000's.
If you have a DVM with a 20 amp setting, you could hook the meter up in series and see how much the plug draws. It will be around 15 amps. This is just as good as pulling the plug. If you happen to be lucky enough to have a meter with at least a 60 amp setting, you could simply hook it up in series at the GP controller, turn the key and test the whole left or right side at once.
If you have a DVM with a 20 amp setting, you could hook the meter up in series and see how much the plug draws. It will be around 15 amps. This is just as good as pulling the plug. If you happen to be lucky enough to have a meter with at least a 60 amp setting, you could simply hook it up in series at the GP controller, turn the key and test the whole left or right side at once.
Correct - both posts define correct methods for glow plug testing
Also, while you're at it, note the condition of the glow-harness wiring and connections:
- female connectors must fit tightly onto the glow-plug spade terminals - high clamping tension ensures full-current electrical connection - loose terminals mean reduced current, minimal glow
- frazzled, broken wire conductors or\and loose crimp means reduced current, minimal glow
- damaged connections\connectors give same results as damaged\failed glow-plugs
To restore correct spade terminal tension, get ur automotive dykes outta the toolbox, use a small jeweler's screwdriver to remove the plastic insulator, observe the as-found spread in the slot that slips over the male spade:
(Place prerequisite precautionary note here):
- now, it doesn't take a brain surgeon to do this, but those, or similar, skills would help: Hulko, the ham-fisted 18-wheeler wrench, is gonna quickly destroy the connector, and prolly the dykes, to boot - Joe, the mechanic, will also likely have problems with this delicate procedure
- look inside the connector insulator at the female spade terminal - you'll notice an upset tab in the terminal which locks the plastic insulator - using the small screwdriver, depress that tab to release the insulator, remove by pulling forward off the terminal
- note that the spade female is constructed of a flat piece with ears, each side ear folded back over the center to form a wide slot - those folded ears spread open with age, heat, and removal\reinsertion, reducing tension required to make proper electrical connection
- now, using the dykes, gently compress each side-edge of the terminal, reducing the depth of the spread - make the folded ear sections closer to the main body
- test the fit after each sequence - female connector should be a tight, secure fit on the male spade
- when so, bend the securing tab out enuff to secure the insulator, insert the terminal into the insulator, and yer good to go
Also, while you're at it, note the condition of the glow-harness wiring and connections:
- female connectors must fit tightly onto the glow-plug spade terminals - high clamping tension ensures full-current electrical connection - loose terminals mean reduced current, minimal glow
- frazzled, broken wire conductors or\and loose crimp means reduced current, minimal glow
- damaged connections\connectors give same results as damaged\failed glow-plugs
To restore correct spade terminal tension, get ur automotive dykes outta the toolbox, use a small jeweler's screwdriver to remove the plastic insulator, observe the as-found spread in the slot that slips over the male spade:
(Place prerequisite precautionary note here):
- now, it doesn't take a brain surgeon to do this, but those, or similar, skills would help: Hulko, the ham-fisted 18-wheeler wrench, is gonna quickly destroy the connector, and prolly the dykes, to boot - Joe, the mechanic, will also likely have problems with this delicate procedure
- look inside the connector insulator at the female spade terminal - you'll notice an upset tab in the terminal which locks the plastic insulator - using the small screwdriver, depress that tab to release the insulator, remove by pulling forward off the terminal
- note that the spade female is constructed of a flat piece with ears, each side ear folded back over the center to form a wide slot - those folded ears spread open with age, heat, and removal\reinsertion, reducing tension required to make proper electrical connection
- now, using the dykes, gently compress each side-edge of the terminal, reducing the depth of the spread - make the folded ear sections closer to the main body
- test the fit after each sequence - female connector should be a tight, secure fit on the male spade
- when so, bend the securing tab out enuff to secure the insulator, insert the terminal into the insulator, and yer good to go
Last edited:
TurboTahoe
Recruit
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Hi there Tim,
Has anyone found a place to guy the OEM glow-plug female spade connectors? I put some OK quality ones in, but was impressed by how robust the OEM items appeared to be. They did also last 13 years before dying. I'd like to find the same.
Also, I seem to recall people saying that the wires used to connect to the glows was not normal electrical wire, but was 'fusible link'.
Anyone care to explain all that?
Thanks,
Rob
Has anyone found a place to guy the OEM glow-plug female spade connectors? I put some OK quality ones in, but was impressed by how robust the OEM items appeared to be. They did also last 13 years before dying. I'd like to find the same.
Also, I seem to recall people saying that the wires used to connect to the glows was not normal electrical wire, but was 'fusible link'.
Anyone care to explain all that?
Thanks,
Rob
RadioMan
Recruit
Fusible links - While they look like wire from the outside they are actually made up of 2 elements that will, by design, melt apart at a specific (well, more or less) current. They are fuses - Hence the name. They are just like regular fuses in that when they fail they are destroyed and must be replaced. Unlike regular fuses they can carry a huge overload for a short period of time without melting. Any low resistance heat producing device (like a glow plug for example) will have a very high current draw at start which will diminish as it heats up. A regular type fuse would fail at that current draw. Some idiots just replace the fusible link with a big old fuse - Don't do it. Fuses are sized to protect the insulation on the wire - They are not sized to protect the terminal device. A fuse that would survive the initial shock can only be used if the wire size feeding the circuit is big enough for that fuse. That wire would have to be resized from the source to the device and any switches in between would also have to be rated for the greater current rating of the fuse. WAY CHEAPER to use a link than a bunch of BIG wire and switches.
ALWAYS KEEP IN MIND -- Fuses are FIRE PROTECTION devices.
ALWAYS KEEP IN MIND -- Fuses are FIRE PROTECTION devices.
SnowDrift
Ultra Conservative. ULTRA!
I've read several threads where the process was described for testing and it doesn't sound like it has changed much over the years. I guess if it was in the technical library section, I missed it, though.
If out of the engine, one test can be to apply 12v to the spade terminal with a battery charger, wait 5 seconds to see if it glows red. Take power lead off after 5 seconds, total time. I assume the glow plug is to be lightly secured in a vise on the hex portion with the vise acting as the ground - is this correct?
If in the engine, amperage can be tested on each bank to see if there is a 60 amp draw for each since each glow plug draws 15 amps.
To be accurate, the resistance test mentioned above where measuring ohms, the 1.2 ohms is best and .6 ohms is weakest - is this correct?
If out of the engine, one test can be to apply 12v to the spade terminal with a battery charger, wait 5 seconds to see if it glows red. Take power lead off after 5 seconds, total time. I assume the glow plug is to be lightly secured in a vise on the hex portion with the vise acting as the ground - is this correct?
If in the engine, amperage can be tested on each bank to see if there is a 60 amp draw for each since each glow plug draws 15 amps.
To be accurate, the resistance test mentioned above where measuring ohms, the 1.2 ohms is best and .6 ohms is weakest - is this correct?
Will L.
Well-Known Member
I completely quit testing glow plugs in the engine. You can ohm or amp meter them.
Problem is as they wear out, get burned up from timing issues, etc this decreases the resistance. As they get soot/fuel caked onto it, the carbon and fuel combo basically builds a carbon pile tester on it. This of course increases the resistance. So you have plugs that have double negative- two bad problems making them barely produce heat- but electrically test perfect.
Rare magic trick? Just the right situation gone bad? Well...
Working in the fleet we would get cold snap and have a couple trucks as “no start”. I would grab my meter and the other less educated guy wiuld just grab new plugs and his socket/ratchet. By time his was running and driving off, mine all tested good so I was started down the diagnostic rabbit hole. After a few times of this occurring- i was there testing them on the bench and hooking up power to see how they heat be new and good used ones.
It didn’t take long before shop policy was R&R plugs. Then once truck is in service, go test the plugs and save the good ones, chuck the bad ones. Then we used up the ones proven good first on non crucial trucks or trucks we could get to easy.
Save money? New set is like $80. Say you are half way through their life. So you have $40 you just wasted. Think how many years that took- you just spent 1 dollar every month and a half. With that money you could buy a cup of coffee for a starving puppy in Uganda. So test the old plugs and save the good ones. Next time buy all new plugs again. After that time you maybe have a complete set of good used plugs so now you can throw them in for free and save the puppy from not having coffee.
If you want to know if they are working in place and actually know? temp gun the individual plugs right where they go in. Faster and measure results instead of theoretical electrical draws and resistance to current and guessing if they are working at 50% or not.
Problem is as they wear out, get burned up from timing issues, etc this decreases the resistance. As they get soot/fuel caked onto it, the carbon and fuel combo basically builds a carbon pile tester on it. This of course increases the resistance. So you have plugs that have double negative- two bad problems making them barely produce heat- but electrically test perfect.
Rare magic trick? Just the right situation gone bad? Well...
Working in the fleet we would get cold snap and have a couple trucks as “no start”. I would grab my meter and the other less educated guy wiuld just grab new plugs and his socket/ratchet. By time his was running and driving off, mine all tested good so I was started down the diagnostic rabbit hole. After a few times of this occurring- i was there testing them on the bench and hooking up power to see how they heat be new and good used ones.
It didn’t take long before shop policy was R&R plugs. Then once truck is in service, go test the plugs and save the good ones, chuck the bad ones. Then we used up the ones proven good first on non crucial trucks or trucks we could get to easy.
Save money? New set is like $80. Say you are half way through their life. So you have $40 you just wasted. Think how many years that took- you just spent 1 dollar every month and a half. With that money you could buy a cup of coffee for a starving puppy in Uganda. So test the old plugs and save the good ones. Next time buy all new plugs again. After that time you maybe have a complete set of good used plugs so now you can throw them in for free and save the puppy from not having coffee.
If you want to know if they are working in place and actually know? temp gun the individual plugs right where they go in. Faster and measure results instead of theoretical electrical draws and resistance to current and guessing if they are working at 50% or not.
SnowDrift
Ultra Conservative. ULTRA!
Sound advice, Will. I'm planning on a new set with the engine project, but since they're all out, I thought it would be a good time to check them just because I'm curious.