New MB owner - 1984 300D - PeachParts Mercedes-Benz Forum

WhoWhat · #1 07-02-2008, 06:46 PM

Just bought my first MB - a 1984 300D. I love this thing.

I'm going to change the rear shocks and front brakes this weekend - bought the parts today. I've read all the posts on here about the rear shocks...seems pretty straightforward. And brakes, they are almost always easy to do.

One question: my glowplug light on my dash stopped coming on today. What does this mean?

Thanks!

Jason
Clarkston, MI
1984 300D

compu_85 · #2 07-02-2008, 06:52 PM

Two or more glow plugs are burnt out. Remove the harness and check them with an ohm meter.

-Jason

techguy512 · #3 07-02-2008, 07:00 PM

Quote:

Originally Posted by compu_85

Remove the harness and check them with an ohm meter.

Actually, it's best to leave the harness on. Just unplug the connector at the relay, and check them all (with your ohm meter) at the connector.

WhoWhat · #4 07-02-2008, 07:19 PM

Cool - thanks. This is my first diesel...so, I'm frankly a bit ignorant. What does the glow plug do? Where is the harness you're talking about?

chetwesley · #5 07-02-2008, 07:25 PM

I am not sure where the harness is, but the glow plugs essentially heat up the air in the cylinders (and therefore the fuel when it is eventually injected) prior to starting the engine (that might be a little simplified or off, but someone will correct me, rest assured).

They are like little stubs of electric stove heating elements that glow hot inside the engine when you turn the key to the position previous to the one that turns the engine over. I believe they may even continue to glow for a short time after the engine starts.

The heat allows the fuel to more easily ignite under compression when starting an engine from cold.

chetwesley · #6 07-02-2008, 07:26 PM

ps: http://en.wikipedia.org/wiki/Glow_plugs

WhoWhat · #7 07-02-2008, 08:20 PM

Thanks. I'm smarter now!

Where are the glowplugs located on my car? I'm thinking they must be near the fuel injectors, since the plug is heating the air where the fuel is injected. True?

Jeremy5848 · #8 07-02-2008, 08:25 PM

Correct. They are on the left (driver) side of the engine and look like small sparkplugs with a small wire running to each one from the glow plug relay, which is on the left inner fender behind the headlight.

WhoWhat · #9 07-02-2008, 08:29 PM

Quote:

Originally Posted by Jeremy5848

Correct. They are on the left (driver) side of the engine and look like small sparkplugs with a small wire running to each one from the glow plug relay, which is on the left inner fender behind the headlight.

So, if I'm reading that correctly, the glowplug can be replaced by unscrewing (?) them away from the engine (like a spark plug), disconnecting them from the wire, and replaced? Seems relatively straightforward...

I'm totally into learning how to work on this thing myself - that's the whole reason I bought this car. Thanks again.

Cr from Texas · #10 07-02-2008, 08:58 PM

Before you do a lot of work, does it still start easily? If so, could be as simple as the dash indicator bulb has burned out. I'd start there.

WhoWhat · #11 07-02-2008, 09:06 PM

Quote:

Originally Posted by Cr from Texas

Before you do a lot of work, does it still start easily? If so, could be as simple as the dash indicator bulb has burned out. I'd start there.

Yeah, it starts without a problem. How could I check the dash bulb?

Cr from Texas · #12 07-02-2008, 09:14 PM

You need to remove the panel under the steering wheel. Reach up to the back of the light and see if you can pull the wire with bulb out. If not, you need to push out the instrument cluster to get to it. The cluster is only pushed into place and relatively easy to push out (a little) from the back. To remove, you have to disconnect speedometer cable, oil line to oil pressure guages, and electrical plugs (watch out for the 12-15 wire plug on the lower left as it likes to come appart instead of unplug - ask me how I know). I think you can get to the bulb without removing the cluster. To get more room and leave everything connected, temorarily release the speedometer cable from it's under hood support to get some slack.

charmalu · #13 07-03-2008, 12:07 AM

also if you go so far as to remove the oil supply line, use 2 wrenches. a 13mm and a 10mm. the 13 is a back up wrench to take the strain off the gauge.

charlie

ImBroke · #14 07-03-2008, 07:39 AM

Sounds like another Mercedes Benz love affair in the works.. Good luck with it, we're here to help.

pdrayton · #15 07-03-2008, 08:56 AM

I would check the glowplugs first - much easier than getting at the bulb.

pull the cover off the glowplug relay (blackbox with removable top cover sitting on the drivers side wheel well in the engine compartment) and pull off the electrical connector that goes to the glowplugs (I think it's the big one - there's two of them). Put the ground of the ohmeter on the engine somewhere and then test each line. You'll find if there's a burnt out glowplug pretty quick.