My glow plug indicator light is not coming on, nor my car is starting because of it. Is my car trying to tell me that it's time for new plugs?? How often should these be changed?? What else can I check? Please shed some light. Thanks!!

82 300d Turbo

I think changing your GPs would solve your problem. They are not a regular mainatence item like spark plugs. Have you adjusted valves and changed out filters ( air,eng oil, power steering & 2 fuel ) ?

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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"

Glow plugs aside, I wonder about the general health of your car. My 81 SD with 290K miles would start without glow plug assist (bad relay) from March through October in San Jose, CA. Took up to 10 seconds of cranking at times but it would start.

Before you get new glow plugs, check all fuses including the 80 amp bare strip fuse atop the glow plug relay.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD
81 300SD (sold)

Yes I have changed filters, etc. But, I have not checked that fuse, and actually don't know where to look for it, where can I find a detailed map of my engine? or, can you please tell me where to look?

Standing in front of the car, with the hood open, look at the wheel well, you will find a black rectangle box. Lift the cover off and you will see a flat piece of aluminum, which is the 80 amp fuse. The box BTW is your glowplug relay.

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Thank you so much!!

Merz82,

Before you replace the GP, find out if the ones you have are getting energized. Does the GP relay click when the key is turned to the run position? If it does check whether there is 12 volts at the GP.

Also, take the 8 hole connector out of the GP relay and check the resistance of each GP in the connector holes to ground. Each GP should read .04 to .08 ohms.

R&R the other connector on the GP relay about 10 times. Sometimes corrosion makes an open circuit between the connector and the GP relay and R&R should work thru it.

P E H

Actually it's between 0.4 to 0.8 ohms (not 0.04 - 0.08 ohms).

Eric

Eric is correct, I was off by one order of magnitude.

The cable to the GP must be removed from the GP relay when measuring the GP resistance to prevent parallel readings that give incorrect results. If you have a bananna plug lead on your meter, its easiest to take the readings in the connector holes.

P E H

I f you don't have a multi tester there is an easier way to test your glow plugs...

Get a 4 foot length of wire (speaker wire will work) strip both ends, unplug connector from GP relay, hold one end of the wire to the + terminal on the battery and touch the other end to your respective GPs (careful not to bump anything else). If you get a spark that plug works if not its time for a new one, work your way down the line.

I just had to replace 3. But my car still started cold on unheated vegetable oil. So if yours won't turn over after a minute or so of cranking my guess is that you've got other issues...

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