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99 cl500 starter/battery warm start problem

3970 Views 10 Replies 7 Participants Last post by  syljua
I should start by saying I’m in love with Ruby! The ride, the power, the grace of this car is amazing.

I’ve spent some serious money at the MB dealer, rear struts, actuators, brakes, rotors, tires, starter, battery, oil pressure sending unit, central locking pump, and last but not least a complete service.

So here is the problem. When she’s cold the engine turns over fast and starts immediately. On short trips she starts right up, no change.
On a longer trip, the car running perfectly, oil pressure and engine temp normal, the battery seems dead when engaging the starter. The engine will barely turn over, service and warning lights go dim, try again and you even hear the tick of what sounds like a completely dead battery.
The first time this happened the dealer said it was the starter and I had it replaced. At the same time we replaced the battery with an almost new one.
I had no problems for a month or so (keep in mind my trips were short around town). Yesterday I drove the car 100 miles, AC on everything working perfect. Turned her off, turned the key on and the engine barely turned over, tried again, completely dead.
I went to my appointment and returned an hour later. The engine turned over very slow but started.
Drove home, again, 100 miles no problems, half the trip at night.

The next morning the car turned over like a highly charged battery. After a 30 minute trip with two very slow starts in between the battery went completely dead again. AAA used a battery pack to jump the car.

I had the MB dealer bring a new battery out. First he tested the battery and said it was good, and then a re-test showed bad. He went ahead and put the new battery in and the engine turned over fast and started. He let the car idle for about 20 minutes, turned it off, same thing, engine wouldn’t turn over.

What should I be looking at?


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Although i'm not sure exactly how to use it, i have a multimeter.
Testing with engine off the meter reads close to 12, i'd say 12+ (no exact science with this cheep meter) with engine running there is no difference...same reading.
Are we on to something?
Thanks for the help,
If your cheap meter is working properly, then you have a charging problem as mentioned. You should see over 14 volts when the car is running. I would expect that you should see the charging system dash warning lamp lighting up telling you that it isn't charging, but you didn't mention a warning lamp. Is the bulb burned out or removed? To check the lamp, turn the ignition to on, but don't start the car. Look at the instrument panel. All the warning lamps should be lit up. This is by design so that the lamps can be checked in this manner. If the charging system warning lamp is not lit up, the bulb is burned out or missing.

If it is just the voltage regulator, the part is cheap and easily available. If there are diode issues as well, I'm not sure how to get your hands on a rectifier. Depending on your confidence as a DIY mechanic, it might be best just to get a fully rebuilt alternator.

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