Last Friday morning the 300D 2.5 wouldn't start - turn the key, and nothing. The idiot lights were on, the glow plug timer light works as usual. After three more attempts, it activated the starter, and just barely turned the engine. It started and ran just fine the day before, and I never saw the charge light come on. So i hopped into the 240D and drove it to work. That evening I put the trickle charger on the battery, thinking the problems was either a dead battery from mechanical failure, or a short or trunk light stuck on, or similar current draw over night.
I went out to find the problem Sat. noonish - first thing was to check the date on the battery - 7/2000 on a 72 month Interstate. Seemed likely that the battery was dead. This car has a shut-off switch installed between the battery negative terminal and the chassis ground. I've been thinking it was another point of failure, and didn't see any value to it, so it's been on my list to be removed when I replace the battery. However, it occurred to me that I could connect an ammeter across the switch terminals, and see if there was a current flowing, when there shouldn't be, and how much, just by flipping the switch. This was much easier than puling the battery terminal, etc. So I did, and saw almost no current (a milliamp or so). The voltage across the battery terminals was almost 13, so I tried to start it. It started just like it's supposed to. I went back and measured the voltage across the battery, and it was still just shy of 13v., even when rev'ing the engine. Hmmmm. Next I clipped the ammeter across the shut-off switch, and still no current. I decided that the alternator was not delivering electricity to the system, so pulled the alternator. The brushes on the regulator were short, and one of them had black carbon burning over most of it's surface. The corresponding slip ring in the alternator was burned over 80% of it's surface. I figured the brushes were the cause, and the battery just drained to the point that it didn't have the juice to turn the starter. The local Bosch parts store was closed by then, so I decided to try the McParts stores in town, and order from Rusty if no one had a new regulator in stock. One store did, so I installed it Sun. and cleaned the slip ring with an abrasive rubbery disk in the Dremel tool, and tested again. Now I had 13.8v. to the battery with the engine running, and 13 amps flowing into the battery at idle. The moral of this story is that the shut-off switch was very handy for trouble shooting the charging/battery system, and a battery that's almost two years beyond warranty can still function, if charged. So I'll be leaving that switch in place, and might even add them to our other cars, should they cross my path. I won';t go searching for them and make the special effort to install them, but if the opportunity should present it's self I will. -- OK Don, KD5NRO Norman, OK "There are three kinds of lies: lies, damn lies, and statistics." -Benjamin Disraeli and/or Mark Twain '90 300D, '87 300SDL, '81 240D, '78 450SLC, '97 Ply Grand Voyager _______________________________________ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
