A little over a year ago, I purchased a completly original 300d from the original owner (who went to the factory in Germany to pick up and tour before importing). The car has over 100k miles but has been expertly serviced.

I am getting her ready for spring and summer drives, but am having trouble with the glow plug system. Here are my symptoms:
1. Glow plug indicator is very dim.
2. Glow plugs take at least 20 seconds to heat(but will start fine after that).
3. After checking the voltage from the 5th cylinder forward (starting at the firewall) my glow plug voltages were as follows 10v, 8v, 2v, 0v, and 0v.
4. Battery voltage with no power is 12v.
5. Battery voltage running is 12v.

Ive been told my glow plug relay is dead...is this true? If not, could someone please give me some direction...keeping her on the road(and shining brightly) makes driving it all the better.

Any help would be appreciated

-threehun

 

The voltage drop from 8 to 2 volts probably means one of the glow plugs has blown itself out and the resistance loop wire is touching ground. (It's probably the one that reads 8 volts). Here's a suggestion:

Remove all of the formed wire links that interconnect the glow plugs to each other. Now take a 12 volt headlight bulb and connect one connector of the bulb to the POSITIVE post of the battery. From the other bulb connector, hook up a wire that you can use as a test lead. Touch it to each one of the insulated threaded connectors on the glow plugs. You will be reading the ground thru the resistance wire (heater) on each. One of them should have a brighter light on the headlight tester indicating that is the guilty glow plug that is shorted to ground.

A regular test light won't draw enough current to tell the difference between a shorted glow plug and a good one.

Another easy way to do it is to merely unscrew each glow plug and look at it closely. The resistance wire will be clearly visible if it is blown.

Fix this soon, you aren't doing your power supply to the glow plugs any good by having the ouput go to a short circuit.

John

 

Thank you for the help 300djd. I plan to look into the prob this weekend. Wish me luck.

After that I hope to correct my final two systems that needs attention -- the cruise control(a must) and a air conditioning check-up (if it is even worth repairing?/charging?). If you know any troubleshooting links for these issues please let me know.

Thanks to all

 

hey, you may want to go over to dieselgiant.com and look at their article on converting series glow plugs to parallel glowplugs. this eliminates the problem of one plug taking out the downstream plugs. and it gives you hotter glow quicker. but it does remove some of the originality of your classic.
I have one of each type, and the parallel sure does start quicker and cleaner than the older serial type... of course my serial type car has over 460000 miles.