Twice in the past week my glow plug light has not registered and I'm pretty sure the glow plugs weren't heating up as the engine struggled to start (in 50 deg. weather). Besides those two times, the plugs have always worked in the two months I've had the car. Now it's getting colder and I want to make sure this won't continue to be a problem. Should I just replace all the GP's or is there some test or simple fix needed here?

Thanks,

Alex
85 300 SD 221k

Since you don't know the history of the GPs I would replace them all and keep the good ones for spars. To test them when you have them out use alagator clips to your battery, one to tip of the GP other to body of GP, they should glow red hot in a couple seconds.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Thanks for the quick reply, SteveO

Do I need to get the glow plug kit, or can I just get five new glow plugs? What is the added benefit of the new "glow plug" kit?

Thanks,

Alex
85 300SD 221k

testing should be completed with a volt meter checking the resistance. Yes the battery test will tell you if there is still connectivity inside the glow plug but it will not tell you the condition of the glow plug itself. I believe the nominal resistance should be less than one ohm for a good glow plug. If you get more than that the filament that is inside is likely starting to burn out and will fail soon. It WILL still glow if this is the case just not as it should.

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.

All you need is the GPs.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Correct, I think the "kit" contains the relay also, you can tell by the price! GP's are around $10 each, the relay is more than ten times that.

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83 SD

84 CD

Next time the light fails, get out of the car, open your hood, take either your Mag-lite from the trunk or your pocket knife from your pocket, and rap the glowplug relay sharply two or three times. See if this magically fixes the problem.

If it does, then your relay is sticking.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Any object will work, the flashlight and pocket knife were the first examples I could think of. I realize now that not everybody is so equipped every time they get in the car.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

It is weird. The glow plug light will come on about every third time i turn key. However, that does not make a difference. I just replaced glow plugs last year. The car starts like it has no glow plugs. Even though relay clicked on and off and gave good voltage to plugs i swapped it with another 300D and got same result -- no glow.

I'll have to check em and try again. The resistance should be less than 1 ohm. Check out diesel giant's awesome glow plug test write up here: http://dieselgiant.com/glowplugrepair.htm

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

Check your strip fuse also.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13