Originally Posted by jkubica (Post 2333708)

But if I count 10 before starting - it starts right away and runs smooth right away.

Originally Posted by Skippy (Post 2333801)

If the light's only staying on a few seconds, you probably have one or more glow plugs out. In Houston weather with five good plugs, your car should start pretty much instantly once the light goes out.

Side note: I have some documents that show my 300D was orignally purchased by a doctor in Houston.

Originally Posted by toomany MBZ (Post 2334131)

If there is enough carbon build up the prechamber won't warm up as much. You want the air to heat up, not a carbon build up.

Originally Posted by toomany MBZ (Post 2334131)

If there is enough carbon build up the prechamber won't warm up as much. You want the air to heat up, not a carbon build up.

Originally Posted by Craig (Post 2334141)

Are you suggesting that he needs to periodically remove the carbon from his glow plugs, in Houston?

Originally Posted by Jeremy5848 (Post 2334303)

The reaming is 90% to prevent sticking, 10% to improve performance. YMMV.

The timer that turns off the pre-glow light on the dash is a different circuit from the glow plug timer. The timer for the light is somewhat temperature sensitive but is more of a "serving suggestion" or "minimum" time before starting. A cold engine will always start more easily and idle more smoothly if you follow Brian's guidelines. Note that the preglow relay has an input from the starter switch: when you release the starter switch after the engine has cranked and caught, the glow plugs will turn off regardless of how long they've been on.

Left to itself, the timer will turn off the glow plugs after about 30 seconds. If you are in a fairly quiet environment, you will hear the relay click off and if you turn on the dome light, it will noticeably brighten when the glow plugs stop drawing down the battery.

Later model M-B diesels also have an "after-glow" circuit that keeps the glow plugs on even after the engine has started. Some people have retrofitted the later relay to their cars. Depending on the year-model of the relay and the engine temperature, the glow plugs will be left on for up to a couple of minutes after the engine starts.

Other folks (including myself -- see this thread for details) have made a modification to the existing circuitry such that if the engine temperature is lower than 50C then the glow plugs stay on for the full 30 seconds. I have found this to be very useful in cold-starting my 1987 300D Turbo (W124, OM603). Combining Brian's advice with the after-glow modification, I pre-glow for ten seconds, then start the engine and let it idle until my custom "after glow" light goes out at 30 seconds. At that point the engine is idling smoothly and the car is ready to drive.

Jeremy