Glow plugs- replace all or none?
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Senior User
Joined: Feb 2006
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From: Candler, NC
Glow plugs- replace all or none?
I've got 3 bad glow plugs in my '93 7.3, I've heard I shouldn't replace part of them, that they will burn out again soon unless I replace them all together. If thats the case about how long could I expect them to last if I replaced just 3?
Thanks
Thanks
Lead Driver
Joined: Jan 2005
Posts: 7,782
Likes: 221
From: Huntington Indiana
Not too long as they was running longer while the other 3 was not workling. It would just be a good idea with the cold weather upon us to just do all at once rather than doing it peacemeal and having to do it several times. Also it could mess up the GP controler/relay.
Posting Guru
Joined: Aug 2006
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From: Kent WA
They may not last too long if you just replace the 3 bad ones, but the other 5 will last longer if you replace the 3 burned ones. If the budget is really tight, go pick up some used ones from a junkyard to replace the burned ones until you can afford to replace all 8....
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Senior User
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From: Candler, NC
Well, I ended up having 6 bad plugs, I guess some more went out since I tested them last week, so I replaced all 8 with motorcrafts. But, after I replaced them, I checked them with a volt meter. I am only getting 9.8v at each plug. I'm only getting 10.5 at the relay. I've got 12.5 on the battery side of relay. I have the controller bypassed with a manual push button switch. The relay is clicking over. Could it be clicking over, but just not carrying enough current? Or are the plugs only supposed to get 9.8 volts?
Posting Guru
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From: Powell River B.C.
With the heavy current draw, they are likely pulling the system down to 9.8 when heated up. E= IR Voltage drop= Current x resistance. with a battery voltage of 12.5 as the current is flowing through the glow plugs the resistance increases, leading to more voltage drop or loss as the system heats up. The plugs are wired up in parrallel, so when one or two fail, more current is flowing throught the rest, thats why they burn out quick when they start to go.
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Senior User
Joined: Feb 2006
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From: Candler, NC
So what should the voltage be at leaving the relay? And at each glow plug shouldn't it be within a couple tenths of a volt difference from the measurement at the relay ?, unless my wires are bad and have a big voltage drop?
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Fleet Mechanic
Joined: Sep 2005
Posts: 1,509
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From: Ladner, British Columbia
Originally Posted by bc56845
I've got 3 bad glow plugs in my '93 7.3, I've heard I shouldn't replace part of them, that they will burn out again soon unless I replace them all together. If thats the case about how long could I expect them to last if I replaced just 3?
Thanks
Thanks
Seb......
Freshman User
Joined: Jul 2006
Posts: 44
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Originally Posted by Hamberger
My advise to you is to change all the plugs at once and make sure you only use BERU plugs that say "Made in Germany" right on the body of the plug.
Seb......
Seb......
Of course I checked them with a hot light, and they were fine. Different voltage maybe? Controller going bad? I'm puzzled.
i ain't rite
Joined: Mar 2005
Posts: 65,453
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From: Marlboro Mental Hospital.
thats because autolites are crap. you are lucky you got them out without pulling the heads. the motocraft-beru plugs take longer to heat up, so they will last longer. i got 16 years out of the set in my 88.
Fleet Mechanic
Joined: Sep 2005
Posts: 1,509
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From: Ladner, British Columbia
If you ever get a chance to cut a burnt out Autolite and a Beru plug tip apart you will see the difference between the two designs. The Autolites come on fast and glow fiercely but burn out faster and swell the tip so you can't get them out of the hole.
The Beru Plugs take longer to glow with a more steady glow as you have noticed in your controller cycling.
There is a huge difference in the design of these plugs and that is what makes the Beru work longterm while the Autolites fail quickly and on top of all things swell up.
The Beru Plugs take longer to glow with a more steady glow as you have noticed in your controller cycling.
There is a huge difference in the design of these plugs and that is what makes the Beru work longterm while the Autolites fail quickly and on top of all things swell up.
