Gabriel,

When you turn the key to the position just before the spring loaded range of motion that engages the starter, you should see a small window on the bottom, usually on the far right side, (edit) of the instrument panel light up a yellow color with an icon that is supposed to represent a glow plug. When the light goes out, then you twist the key against the spring load and engage the starter. If your light is not lighting up chances are you have a few glow plugs that are burned out. If that is the case the car will be very difficult to start in colder weather, and it is common to see evidence of non-ignition of the Diesel mist injected into the cylinders with the bad plugs.

There seems to be a "code" with my 1982 240D that indicates how bad the plugs are. If the light fails to light and I cycle the key to the zero position and back to the glow plug position, and then the light comes on, I have one plug out. If it fails to come on the second try, I have more than one plug out.

With everything working as intended, the car should start in less than a 5 seconds of cranking, and possibly blow a black cloud out, then settle down to a nice even idle in 10 to 20 seconds. With plugs not working the ignition process is retarded by the cooling effects of the Diesel fuel evaporating, until the engine goes through enough cycles, and idles fast enough to "collect" enough heat until the injected fuel ignites. This can take a 30 to 60 seconds, or, if the engine has marginal compression, the injectors are spewing a stream instead of a mist, or the valves are not properly adjusted, it can last for a few minutes.

In any case you need to have the glow plugs checked and replaced. I always replace all of them in one shot, as they are not that expensive, my car has four, my daughter drives it in Upstate NY (165 miles away) and I don't like being called with problems that require a day of driving to fix, and if they are the same age, chances are they going to all fail within a pretty similar interval. It is a pretty simple do-it-yourself task. Check the board for lots of posts on the details of doing it. If you can work with gloves on, do it as I always end up gouging my hands on little sharp things in the area. Good luck, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)