Temp sensor for glow plugs system
Fleet Owner
Joined: Jul 2006
Posts: 20,322
Likes: 789
From: Mi'kma'ki
it's actually just done via the resistance difference in the temperature change through the ground.there is no devoted sensor.its quite basic really and works well.
what kind of issue are you having? not long enough of a glow time when the block is cold i presume?
your working on the '90 in your signature right?
this one helps you test the '87 - 94 system step by step completely via info from the haynes diesel techbook #10330:
(about the books best point.few other good things in it.but not much.)
https://www.ford-trucks.com/forums/1...low-plugs.html
what kind of issue are you having? not long enough of a glow time when the block is cold i presume?
your working on the '90 in your signature right?
this one helps you test the '87 - 94 system step by step completely via info from the haynes diesel techbook #10330:
(about the books best point.few other good things in it.but not much.)
https://www.ford-trucks.com/forums/1...low-plugs.html
Fleet Mechanic
Joined: Jan 2011
Posts: 1,709
Likes: 4
From: 8600 ft in Colo
Yeah, what HDXLT said. The resistance in the glow plugs changes with temperature, and the controller senses this resistance. That's why one or two bad plugs is such a problem. If there's a burned out plug, the resistance of the total system goes up, the controller reads this as a warmer engine, and turns the plugs on for a shorter time...
Thread Starter
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Senior User
Joined: Jan 2007
Posts: 298
Likes: 1
From: Mexico
Yes, it is for my 90 7.3NA. I live in the tropics so the overnight low temperature is in the upper 60’s.
My glow plug set-up uses a 3-way switch. Dave S from WV recommended this setup. I can start with the controller, momentary for manual, or without using the glow plugs at all when engine is warm. I can use the manual side of the switch but like to use the controller to detect any problems in the system.
On the first start of the day, the WTS light comes on for 4-7 seconds. I have tested all the plugs (Beru) with a test light and they are good. I tested the wires to the plugs and they are getting power.
I can get it started without problems manually but only holding the switch for 10 seconds. When I use the controller, I might have to cycle it twice to start.
Now here is the weird thing, when I was checking the plugs I accidently pulled the wire off the sensor to the cold start solenoid. The plugs glowed for 8 seconds after that. I waited 5 minutes and hooked the sensor back up and I only got 4 seconds. So why is this sensor affecting my glow time?
My glow plug set-up uses a 3-way switch. Dave S from WV recommended this setup. I can start with the controller, momentary for manual, or without using the glow plugs at all when engine is warm. I can use the manual side of the switch but like to use the controller to detect any problems in the system.
On the first start of the day, the WTS light comes on for 4-7 seconds. I have tested all the plugs (Beru) with a test light and they are good. I tested the wires to the plugs and they are getting power.
I can get it started without problems manually but only holding the switch for 10 seconds. When I use the controller, I might have to cycle it twice to start.
Now here is the weird thing, when I was checking the plugs I accidently pulled the wire off the sensor to the cold start solenoid. The plugs glowed for 8 seconds after that. I waited 5 minutes and hooked the sensor back up and I only got 4 seconds. So why is this sensor affecting my glow time?
Methanoholic
Joined: Mar 2009
Posts: 6,442
Likes: 8
From: Maine (NorCal Native)
That is a good question ...
The Cold Start Advance Thermal Switch controls only the High Idle Solenoid and The Cold Start Solenoid and activates only when the motor water temp is at 112F or lower.
It is not directly connected to the Glow System other then drawing on the same 12v system.
A test light is not a definitive answer for good or bad glow plugs, the only definitive method is with an Ohm meter, between .5 and 1 Ohm. I guess one could pull them, apply 10.5 volts to them and watch them get hot or not.
-Enjoy
fh : )_~
The Cold Start Advance Thermal Switch controls only the High Idle Solenoid and The Cold Start Solenoid and activates only when the motor water temp is at 112F or lower.
It is not directly connected to the Glow System other then drawing on the same 12v system.
A test light is not a definitive answer for good or bad glow plugs, the only definitive method is with an Ohm meter, between .5 and 1 Ohm. I guess one could pull them, apply 10.5 volts to them and watch them get hot or not.
-Enjoy
fh : )_~
Senior User
Joined: May 2010
Posts: 288
Likes: 0
From: Oregon
Correct. But if the test light doesn't light up then the glowplug is definitely bad. If it does light up the plug can be weak, borderline, or just fine.
Thread Starter
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Senior User
Joined: Jan 2007
Posts: 298
Likes: 1
From: Mexico
it's actually just done via the resistance difference in the temperature change through the ground.there is no devoted sensor.its quite basic really and works well.
what kind of issue are you having? not long enough of a glow time when the block is cold i presume?
your working on the '90 in your signature right?
this one helps you test the '87 - 94 system step by step completely via info from the haynes diesel techbook #10330:
(about the books best point.few other good things in it.but not much.)
https://www.ford-trucks.com/forums/1...low-plugs.html
what kind of issue are you having? not long enough of a glow time when the block is cold i presume?
your working on the '90 in your signature right?
this one helps you test the '87 - 94 system step by step completely via info from the haynes diesel techbook #10330:
(about the books best point.few other good things in it.but not much.)
https://www.ford-trucks.com/forums/1...low-plugs.html
If I am reading this correctly with 70 degree engine/controller temp I would only expect to get a 3-5 second glow time?
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Logistics Pro
Joined: Sep 2010
Posts: 4,411
Likes: 4
From: Victor, MT
Another thing in case your changing glow plugs, read this thread that I created for removal of stuck glow plugs in the event you dont have motorcraft GP's:
https://www.ford-trucks.com/forums/1...g-in-head.html
https://www.ford-trucks.com/forums/1...g-in-head.html
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Post Fiend
Joined: Feb 2009
Posts: 8,005
Likes: 7
From: Ottawa, Ontario
After my little experience on my motorhome, I will never test glow plugs with a test light, ohm meter, or any of that crap.
If I suspect bad plugs, I pull 'em out, and test directly on the battery!
Few years back, the WTS light would come on for 1-2 secs. So ok I taught it must be a few bad glow plugs, check 'em all. All checked out good. Checked 'em all a 2nd time, all good, ok maybe bad controller, replace controller, nope same story.
God damnit! So pull all 8 plugs, and test 'em right on the battery! Found 3 bad!!!
The 3 bad ones were showing good resistance, and lighted up a test light, but on the battery, were only heating up, BUT NOT glowing red like they're suppose to.
Replaced those 3, bam been working great since! So now I spent 150$ on a controller for no reason. So now I have it as a spare.
No more ohm meter/test light testing for me, it cost me!
At the same time, by pulling out your plugs for checking them, you can also inspect them for swelling, etc. and it keeps 'em from being in there to long and seizing.
If I suspect bad plugs, I pull 'em out, and test directly on the battery!
Few years back, the WTS light would come on for 1-2 secs. So ok I taught it must be a few bad glow plugs, check 'em all. All checked out good. Checked 'em all a 2nd time, all good, ok maybe bad controller, replace controller, nope same story.
God damnit! So pull all 8 plugs, and test 'em right on the battery! Found 3 bad!!!
The 3 bad ones were showing good resistance, and lighted up a test light, but on the battery, were only heating up, BUT NOT glowing red like they're suppose to.
Replaced those 3, bam been working great since! So now I spent 150$ on a controller for no reason. So now I have it as a spare.
No more ohm meter/test light testing for me, it cost me!
At the same time, by pulling out your plugs for checking them, you can also inspect them for swelling, etc. and it keeps 'em from being in there to long and seizing.
Elder User
Joined: May 2005
Posts: 567
Likes: 1
After my little experience on my motorhome, I will never test glow plugs with a test light, ohm meter, or any of that crap.
If I suspect bad plugs, I pull 'em out, and test directly on the battery!
Few years back, the WTS light would come on for 1-2 secs. So ok I taught it must be a few bad glow plugs, check 'em all. All checked out good. Checked 'em all a 2nd time, all good, ok maybe bad controller, replace controller, nope same story.
God damnit! So pull all 8 plugs, and test 'em right on the battery! Found 3 bad!!!
The 3 bad ones were showing good resistance, and lighted up a test light, but on the battery, were only heating up, BUT NOT glowing red like they're suppose to.
Replaced those 3, bam been working great since! So now I spent 150$ on a controller for no reason. So now I have it as a spare.
No more ohm meter/test light testing for me, it cost me!
At the same time, by pulling out your plugs for checking them, you can also inspect them for swelling, etc. and it keeps 'em from being in there to long and seizing.
If I suspect bad plugs, I pull 'em out, and test directly on the battery!
Few years back, the WTS light would come on for 1-2 secs. So ok I taught it must be a few bad glow plugs, check 'em all. All checked out good. Checked 'em all a 2nd time, all good, ok maybe bad controller, replace controller, nope same story.
God damnit! So pull all 8 plugs, and test 'em right on the battery! Found 3 bad!!!
The 3 bad ones were showing good resistance, and lighted up a test light, but on the battery, were only heating up, BUT NOT glowing red like they're suppose to.
Replaced those 3, bam been working great since! So now I spent 150$ on a controller for no reason. So now I have it as a spare.
No more ohm meter/test light testing for me, it cost me!
At the same time, by pulling out your plugs for checking them, you can also inspect them for swelling, etc. and it keeps 'em from being in there to long and seizing.
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