Hi,

My 1974 240d's glow plug was working great 2 days ago when the temp. in DC was around 34-36 degree F. Then yesterday we had a snow storm (1") and the temp. dipped into the teens (around 15-18 F). The car is also left outside.

Now when I try to warm up the glow plug (pulling on the ****), it won't light up even after 1 minute of pulling on the **** and my car won't start. Today was the first time the temp. increased to around 32 F, but the glow plug still won't light up.

Why won't my glow plug work.

 

Where are the plugs located under the hood and how can I test them? I'm sure there are many posts so any links would be greatly appreciated. Thanks again and you can tell I'm a novice and just got this car.

 

See the Yellow arrows on the Pic. In the Pic the Glow PLug at the rear is removed.

If you remove them be sure to note exacly how the wires are hooked up in regards to the white insulators.
Also trace the Wires backwards see if you have a Fuse on the Fire Wall.

If you plan to keep the Car for a long time many people have found replacing the Stock Loop/Filament type Glow Plugs and nearly all of that wiring a good upgrade.

The system is simpler, heat faster and get hotter then the older type Glow Plugs. Another big advantage is the way the Newer Glow Plugs are Wired if one Glow Plug burns out the other 3 will still work.

In the 2nd pic you can purchase the Bosch 80035 Glow Plugs separately and make your own Wires.

 

Thanks all for your answer, and I have an update.

The other day the temp. got up to 45 degrees F and the glow plugs light up and the car started. So I thought I it was just an issue with the weather being too cold.

The next day the temp. got up to 65 degrees F and a little light rain. When I tried to start the car, the glow plug wouldn't light up.

So before I take apart and replace the glow plugs, is there a way to test the glow plugs with a AMP or Volt meter? If so how should I test? Again, keep in mind I'm a novice.

 

They can be checked with a Volt Meter while they are still installed with the **** pulled to the preglow position. However, if your Fuse is burnt indicating a short; installing another Fuse and trying to do the test would likely result in another Burnt Fuse as you had not found the Short Circuit.

However, I cannot describe the method to do the whole teste exactly.

You will need to search this forum or another Mercedes forum to find the specific way to check them.

Often when they are removed what you find is that the Loop/Filiment is burned. That creats an open circuit and none of the other Plugs will work because they are wired in series; sort of chained together.

If those zig-zag Resistance Wires are touching the Engine Block that will create an instant short circuit.