I have a 1979 300SD with 256,000 miles on it. I haven't used it much as I
have the wagon as a daily driver. It starts fine cold after i replaced the
one bad glow plug (it only needed #3 and it's the easiest to replace), and
starts fine when warm.
If i start it cold and only go a very short distance, the glow plug relay
assumes it's warmed up and it won't re-start unless I either wait until it's
dead cold or i jump the glow plugs.
Has anyone fooled around with adding a resistor or something to the temp
sensor to let a tired engine start easier?
--
Stupendous Man,
Defender of Freedom, Advocate of Liberty

I would change the glow plug relay... the new one will let it run another 3
minutes before it shuts off... But as with any relay, it should have turned
the glow plug system on again as long the ignition was turned off and then
back on.

Do you suppose the one AC brand plug may be different than the ones of
unknown age causing the problem? I remember with VW diesels there was a
change to a "fast glow" system, plaugs and relay were swapped.

"Stupendous Man" <spam (AT) trap (DOT) com> wrote


Measure the resistance of the plug. Since all the power is used to make
heat, there should be a linear relationship between the resistance and the
amount of heat it produces.

To test your relay, hook up your meter and see if you have voltage and for
how long after you turn the key on.

You could also have a carbon problem. sometime there is a carbon build up in
the glow plug chamber. They sell a tool to clear this out.

--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.

Ditto on Roger's suggestion.

All your glow plugs should be about 0.6 ohm... For your car, glow plugs are
dirt cheap... why bother anything other than Bosch? Ebay seller sells the
whole kit cheaper than glow plugs at dealer.

For your car, glow plugs are
my thoughts exactly, but there was a set in the glove box when i got the car

I put in the other 4 plugs ysterday, tested it once, and sold the car today.
Now back to the 81 Wagon and other projects
Thanks.
--
Stupendous Man,
Defender of Freedom, Advocate of Liberty