PeachParts Mercedes-Benz Forum - View Single Post - ‘71 220D: At how low temp. will it start with bad plugs?

JimSmith · #10 02-14-2002, 08:50 PM

atikovi,

I am not clear on the procedure you are using. I had a 1971 220D for a long time in the family, and replaced it with a 1975 240D. Both of them had the knob you pull out of the dash to the left of the steering wheel to start. As psfred has noted, the knob has a couple of positions as you manipulate it to make different things happen. If you are already familiar with the knob's functions and positions, then the rest of this is probably not of use to you. But, just in case you are not familiar, I have provided some detail on how the thing is supposed to work.

In the off position the knob is all the way in against the dash. When you pull it out it kind of pops into the "run" position. To start you have to pull it out and hold it out against a spring preload that wants to push it back to run position. The "out against the spring load" position is the glow plug energizing position. If you do not hold it out there, hard against the end of the spring travel, the plugs will not get energized. You can tell, when you pull it out, if you watch the red lights in the instrument panel dim, that you have reached the point of energizing the glow plugs. You hold the knob there for a twenty or more seconds and the glow plug filament on the dash should start to turn dull red, then get brighter and turn orange. When it is in the orange range, you pull even harder and the starter engages. Once started you let go of the knob and the spring pulls/pushes it back to the "run" positon. To shut the car off you push the knob into the dash until knob, and the engine, stops.

If you cannot see the dash lights dim, you likely are not getting juice to the glow plugs. That can be the fault of a failed fuse, a loose connection on the glow plug wiring, or the dash pull-knob switch.

On my 220D the last glow plug (#4 cylinder) had the wire delivering power attached to it. While I was in Aspen skiing, the car suddenly would not start. I was pretty anxious because the car was relatively new and this was the first time the car failed to start (I also learned about Diesel fuel gelling in the cold that trip). After a good bit of struggling I noticed the dash lights did not dim. So I checked fuses and then connections. The connection to that last glow plug had broken off the wire due to vibration. I found a replacement eye hole type connector and crimped it on,made the connection and the problem was solved.

It actually took me a few days to figure this out, but since the car was a manual transmission unit, even without glow plugs I could push start it. Just get it up to about trotting speed or higher and, with the knob in the glow plug position (optimistic) or in the run position, put it in second and drop the clutch. Even in bitter sub-zero cold I have always been able to start these things by pushing them.

My 240D dash switch died in the glow plug position as psfred suggested might be the case with your car. My 240D also had a starter interlock, courtesy of the US DOT for 1975 model year cars with manuals, which cut the starter out of the circuit if the car was not in neutral. So, I learned to start the car by putting it in gear, then pulling the knob all the way out of the dash and holding it there for 30 to 40 seconds, and then dropping the shifter to neutral. Not exactly what MB had in mind, but, since the system was designed to keep the plugs glowing when the starter circuit was engaged by the dash knob, it worked that way at least as long as it worked the originally intended way.

Some other things that can be afflicting your car could be tight valves, as when they are out of adjustment they get tight and then do not open and close according to plan. This means low compression and can be fixed with a valve adjustment. Or, the starter can be getting tired and the motor is turning over too slowly. Or you have too heavy an oil in the car and the viscosity of the stuff when it is cold is adding enough load to slow the starter down. If you just got the car, it may need some routine service, like a valve adjustment and an oil change. I can tell you my 1982 240D with 280,000 miles loves Mobil Delvac 1. No problems starting this car this winter in Troy, New York where it has been in the single digits lately.

Hope all this helped, good luck, Jim