420SEL intermittant starter problem - infuriating!
 

Searched, but can't find reference to situation exactly matching mine... Hope someone can help solve this really infuriating problem.

Here are the facts:

1) Over the last two weeks, I've noticed the starter cranking a little less energetically on startups. (Car is garaged, nevertheless, I figured it was the onset of the colder weather that was probably to blame. This assumption now appears to have been wrong.)

2) This morning--not particularly cold--the starter really sounded like it was struggling, and it took two tries to get the engine to turnover. (As always, once she starts-up, it's smooth sailing all the way.)

3) Arrived at my destination about 40 minutes later. Car sat for about 4 hours. Started up thereafter. Went for lunch; parked at the restaurant; afterward, engine started-up again. Made one final stop (the fateful one) at the local Home Depot. Was in the store for about 20 minutes, after which I tried to get my beloved 420 to start... Nada! Starter refused to crank at all.

4) Tried everything obvious (checked shifter position, fluid levels, battery connections, fuses, listened for fuel pumps); all checked-out fine. Note: New battery (about 3 months old) and new alternator (about 6 months old); I really don't think the problem is with them...

4) Called AAA for a tow to my trusted indy. Tow operator tried, but couldn't get her to start either, and re-checked the battery and essentially retraced my steps confirming that the problem lay elsewhere. Tow on the flatbed took about 40 minutes.

5) Upon arriving at the indy's garage (he's closed until Monday) and thanking/tipping the tow operator, I climbed into my 420 to await a pick-up by my wife in our other car. While sitting there in the dark, and just for the heck of it, I stuck the key in the ignition, and--bingo--car started right up!!! :rolleyes:

That's the story so far... I opted to leave the car there for my mechanic to hopefully diagnose and correct, but I'd sure appreciate some insights into the most likely source of this intermittant problem.

Any educated guesses? (I'll report back on what the indy comes up with in any case.)

Hopefully the car will cooperate with your technician. It sounds a lot like an intermittant resistance in the starter circuit.

This could be anywhere between the individual cells of the battery to the armature of the starter. Very simple to trace when the problem exists. Almost impossible when it doesn't.

The fact that your problem occured after some driving could lay blame on the starter as armature problems often occur hot.

My money is on corroded electrical connections that lead to a broken wire end that is now intermittently making enough contact to close the circuit.

Starter
 

Based on all of the info provided, I would put my money on the starter. I think Bosch makes them and brand new ones are available. Let me know what the mechanic finds as the problem.

I had the same symptoms on my 420. It cost $44 and change for a set of new brushes. Works great now. Of course, I R&R'ed the starter myself. Requres a 10 mm allen socket, swivel head ratchet, wobbly adapter and three feet of extension.

Technician opted to replace the starter
 

Well... I'm $288 poorer; but the mobile bank vault is back on the road again!

Technician promptly identified the starter as the source of my problems. He noted that the device was drawing way too much current (though he did express some surprise afterward that the solenoid was in such good shape). Anyway, he recommended replacing the starter, which I promptly okayed. (It was the original starter--nearly 15 years old.)

1 hour of labor later--which included 25 successive and successful restarts of the engine--and my tech called with the "all clear".

Thanks to those who responded. Your combined expertise bolsters my confidence that this problem is now history.;)