Guys,

This was a "hot" topic las summer in the warmer weather and there were a number of posts on the subject. It is not clear in my memory whether or not the people reporting the problems fixed them and closed the threads or not. But a search will turn up a bunch of similar experiences.

The power from the battery goes from the battery to the light switch on the dash, and from there to the starter switch, on to the rest of the fuse panel and to the starter solenoid when the key is twisted to the various positions. So, the problem can only be in a few of these areas, and it seems to be more of a problem when the engine is hot, in warmer weather.

Poor contact anywhere along the path is possible, and as someone noted recently, it is not impossible to power all the wimpy loads, like the dash lights, buzzers, etc. with a poor connection as they draw very little current. The higher loads, especially the glow plugs, solenoid and starter, will draw much higher currents and cause the existence of a poor, loose, corroded or otherwise imperfect electrical connection to become apparent. The connection heats up quickly and the resistance across the poor connection increases, dropping the Amperes passing through it substantially or completely. So, check the connections, especially the ground to the battery, the connection at the solenoid, and the starter power (thick wire to the starter), as well as those to the fuse box, key and light switch.

It is feasible the electrical part of the starter switch is dirty and worn. I believe this can be replaced seperately. Detailed instructions on this and other starter switch repairs can be found using the search function.

If all that is ok you should be able to reproduce the problem when it occurs by by-passing the key operated starter switch. If the problem occurs with the solenoid powered directly from the battery, meaning you get no response, no clicking of the solenoid, you probably have a bad solenoid. I would replace the starter with a rebuilt one from FastLane. Get the heavy duty one.

If the solenoid clicks when bypassed, or when the key is used and the car does not start (with good, clean connections), the problem is the starter. In my experience this is a winding insulation failure that shows up at elevated temperatures. All wire insulation materials degrade when exposed to heat over time. After a while this is not recoverable when the windings are cool. It is a symptom of an over used starter, and is something Diesels do more to starters than gas cars, typically. Long cranking episodes will overheat the windings, causing the insulation to degrade in any weather. The damage is cumulative, so it takes time to turn into a problem you notice. This degradation is first noticed when the starter is at a high temperature such as after a long run, and being parked when it is warm outside and the underhood temperatures soar. It gets worse over time until it becomes apparent at lower ambient temperatures. Finally, the starter will be unable to sustain a torque level to keep the engine turning fast enough to get it to start when the engine is hot or warm.

Since the starter is located near the exhaust system, and close to the engine, it gets exposed to a lot of insulation degrading temperatures so this is not someting you can avoid by some activity like letting the turbo cool down. When the problem gets to the point where it influences the functionality of the vehicle, the starter again needs to be replaced with a rebuilt one. I like the FastLane units because they are rebuilt by Bosch, and include new wiring with new insulation. Most rebuilt units have new mechanical stuff but not new windings. They are not as expensive, but they do not address the main problem with a worn out Diesel starter. So you find your "new" starter exhibiting the same old symptoms in short order.

I hope all this helps you. If you do a search on the subject you will find this is not a unique problem you are facing. 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)