Glow Plug Light '77 240D
 

The glow plug light on my 1977 240D has failed to come on two times now. Once, two weeks ago and this past Friday. On Friday, I turned the key three times with a one minute space and no light. Tried cranking it the first time in case it was the bulb--no go. Waited five minutes and it the light came on and the car started.

Any ideas--Should I replace the glow plugs or would that just be throwing money at the problem?

By the way. Drove the car from Austin, TX to Orlando, Fl leaving last Wednesday night. 22 hours, 1187 miles, 27.85 MPG

Thanks

Glow Plug Light Randomness '77 240D
 

Any Ideas?

First check the inline bar fuse on the hotwire at the firewall. If it's roasted, then piece of wire or cut up soda can will substitute.

Inline bar fuse
 

240DieselDog,

Thanks! I checked out the inline bar fuse and it was fine. Back to the drawing board.

Then pull the glow plugs starting with #4, first on the circuit. Loop style plugs can burn out - easily detected with visual inspection. The only trick is lining up the heavy guage wire exactly as it was, alternating between upper and lower contact points.

Scorched my own #4 GP once and it disabled the entire system causing a zero GP light situation.

If you find a burned out plug but have no replacement, relocate it to #1 cylinder and the other 3 should heat up.

You have series glow plugs so basically they are most likely okay. Sounds like the relay does no longer reliabily turn on. In just my opinion would try another relay first. Could be an oxidized connection or even a failing key switch as well though but again the old tired relay would be a suspect first. One other thing I should mention is once in awhile one of my cars the 77 300d does exactly the same thing. I just turn key on and off a couple of times till light comes on. I have never troubleshot this problem but if car was in daily use would always keep a jumper in trunk so in the event of total failure would bridge positive battery terminal to top of glow plug chain to get vehicle started. The older relays are not in demand as much as the newer style for parellel plugs so a junk yard replacement is a possibility. A search of the archives is in order as well as the problem is pretty common I think. :) (intermittent glow plug function) (the relay is located above drivers feet is silver in colour and has a machine screw and nut to fasten it to pedal bracket support if you do not have location information as unlike the newer and different ones it is not in plain sight. I only threw this in as your service information may be limited)

Don't think that will work, DieselDog. You might short it out
 

after moving it and get by that way??

Don't ask me how I know you can make toast under the hood if you hook all the resistance wires up to the outer contacts. the engine doesn't start very quickly that way either.... :o

Sidebar of interest...... glow plugs arent the be-all, end-all, last word in starting a diesel engine.

Truck part shops sell small $5 camping size, propane style orange cannisters of diesel starting fluid, used in commercial rigs that have NO glow plugs. Just attach an ordinary propane torch head to the tank, open the valve and stick the tank with torch head facing down into the air intake manifold, then git inside and start the car.

Another interesting option that skips glow plugs entirely is manifold heaters. A series of heavy duty electric coils that get red hot at strartup in the manifold passages through which air travels, it heats the air instead of the fuel as regular glow plugs do.

andersbenz,

First, see if you have voltage at #4 GP. If not, something in the GP relay circuit isn't working. If you have voltage at #4 GP, try the test below.

Make a short (~4 inch) jumper cable with Clips on each end. When the GP do not work (and are turned on), short each GP with the jumper until U find a bad one.

When I drove 190D/220D/240D cars I always carried the jumper described above in the car. It got me started a few times when a GP burned out.

You should use 12 gage wire and clips heavy enough to carry the GP current.

P E H

hey dude well it might sound dumb to some people but i had a glow plug light problem on a 240D before and i thought it was the ignition switch but it was not! it was the Battery!!! i changed the weak battery and now the light comes on! MB told me if MB diesel's have a the wrong battery in or a battery that was short circuited the glow plug light will fail but you still can crank it! weird huh? well i learn something new everyday check your battery man! check your key switch, GP relay, fuse on the fire wall and the wiring. ill say it again it happend too on my w123 300D to!! i had to change the battery because the GP light would not come on! weird huh but it was true for my car and my custumers car! cya....

this dude is giving you a good trick i have done that many many times my self and it work if you have a bad glow plug very good trick! anybody should put that in their memory banks! :D;)

MBdiesel Freak,

What do they mean by the wrong battery? A 6 volt or 24 volt battery? I don't believe the electrical system will know the difference in any 12 volt battery as long as it has enough current capacity.

GP lights are known for being intermittant. Yours will probably not work again and then U can try the tests.

P E H

For us dufuses, specifically what will I be doing and how will I know when I've found a bad plug?

And how will I use this jumper to start the car?

Contrary to what was posted earlier, I don't believe that switching a bad plug to the #1 position will help. With series plugs, the current has to run thru all plugs to ground. The ground goes from number one to the block. If #1 is burned out, the circuit cannot be completed to ground and none of the plugs will work.
If the relay is bad, you can jump from the positive post on the battery to #4 plug. This will energize all the plugs if they are good and you can start it.

I'm not sure what PEH means. I don't know how you can tell a good plug from a bad plug. I think that if there is a bad plug in a series system, you can bypass it by jumping from the heavy wire coming in to the heavy wire going out and complete the circuit that way, energizing the rest of the functioning plugs.

Ok, this is good to know. I will make a wire of the appropriate length with some clips. I guess in a pinch one could use jumper cables?

Well, you can test it if you've got a meter that does resistance. Infinite resistance = bad plug. But the post implied you could do it with nothing more than a wire. THAT'S a trick I'd like to learn.


Question: this morning, the light came on again (yes, I'm actually commuting to work in a 26-year-old car. Not sure what this says about me.) Is it possible the relay is set to cut out altogether at temps over about 85F? I only noticed the light starting to not come on last week (after I got it back from the a/c repair place :mad:), so it doesn't seem likely because we've had hot temps all month. But going over it in my head, the times when the light comes on seem to be cooler. Maybe I will start logging when it comes on and doesn't. (This is the first summer I've had the car).

BTW, does anyone just disconnect their glow system in summer? Seems to me I'm wearing out my plugs and relay for no reason June-September.