A thief broke out the front window of my '97 E300D last week to steal my daughter's school backpack .... nothing else was damaged just the window was shattered. The car sat for a few days until the glass shop got in the part and replaced it. The next morning the car wouldn't start so I put a battery charger on it ..... The battery is about two years old and it hasn't given me a problem; however, I noticed that the charger never transitioned to zero amps after running it for five 90 minute cycles .... so I'm thinking there is a battery drain somewhere ..... probably a large one. I then noticed that the dome lights (front and rear) don't come on when the doors are opened (any of the four) but the security system seems to be functioning normally. I seem to remember someone on the forum having a similar problem but I couldn't find the thread when I searched .... hoping someone this morning knows the easy fix or where to point me to investigate!

Thanks in advance.

Checked the voltage under starting and running conditions and all is normal .... draw down to about 11.5V under glow .... 10V under start .... and maxes out at 13.7V at 4,000 rpm. I took the rear seat out to check fuses and noticed that the rear dome lights had come on and the battery was extremely hot ..... so I disconnected the negative cable to allow it to cool. I'm thinking that something must have gotten shorted out in the door panel ..... any thoughts?

here is a project i have been meaning to do: take a burned out fuse and solder two probe leads into it. the other end, connect to your multimeter (10A jacks). then by swapping the test fuse from circuit to circuit you can see how much current is flowing through each. i'm sure your car has a number more fuses than mine, but provided that the leak isn't in the starter/glow plugs circuitry, it should be findable in this fashion.

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'77 240D, 504H, OM617.952, etc.

I took the car to Sears and they replaced the battery ...... the car worked fine for a couple of days then dead battery again. Checked the drain on the battery when the ignition is off and it was within specs .... so the car is apparently draining the battery when operating! Took the car to my independent mechanic and they said I needed a new alternator and that the battery was week. After replacing the alternator and a battery recharge the car worked fine for a couple of days then dead battery again. Took the car back to Sears and they replaced the battery a second time and sent me back to my mechanic with their diagnosis that the alternator was bad. Just dropped the car off with the mechanic ...... personally I don't think it is the battery or the alternator but something must be on draining power beyond what the alternator can produce when the vehicle is operating ..... my guess is that the glow plugs may be stuck in afterglow .... but we'll see what the mechanic says this time around. Any suggestions as to where to look would be much appreciated.

My guess would be the same as yours. Glow plugs are about the only thing I would think that could put such a draw on the system.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Do you run short trips? It is difficult to deplete the battery when the car is operating and with a working alternator. It needs to use up all the juice from the alternator plus some more from the battery. GP is a remote possibilities, but I doubt it, and the car may not run right with GP on. There are a few things you can do but it takes patience.

1) Disconnect battery every night and see what happens?
2) Disconnect battery after car started. If there is a massive drain then the engine speed may change due to the alternator load. ( with or without battery disconnected. ).
3) Remove fuse one by one and see what is draining the battery.

Good luck.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

With all due respect, I don't believe that you should disconnect the battery while the car is running. See below:

The moment he disconnects either lead from your battery, it's entirely possible he caused thousands of dollars in damage. Here's why...

Your battery does more than just yield electricity. It also shorts AC, spikes and transients to ground. Removing the battery from the circuit allows those spikes and transients to travel around, endangering every semiconductor circuit in your car. The ECU, the speed sensitive steering, the memory seat adjustments, the cruise control, and even the car's stereo.

Even if your computers and stereo remain intact, in a great many cases removing the battery burns out the diodes in the alternator, necessitating a new alternator. If disconnecting the battery interferes with the voltage regulator's control voltage input, it's even possible for the alternator to put out hundreds of volts, frying everything.

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96 E300d

Just disconnect the glow plugs plug after every startup. Then reinstall it just prior to starting the car again. This will eliminate or indicate if glow plugs are coming on when they should not.

Unfortunatly technically they can activate even with the car turned off as well. Their main power supply is direct to the battery basically.

It is an old very poor ideal to test if the alternator is putting out by lifting a battery terminal with the engine running. You will get away with it sometimes. The time will come though when you will not. At that point it can really cost you.

Your car is also new enough to be very careful about boosting it with another vehicle or giving a boost. If you must just let the car boosting charge the other vehicles battery for awhile. Disconnect the boost before the other vehicle starts to try cranking. Again this is another way to potentialy cause damage by just running booster cables over to the other vehicle and cranking it. You will get away with it most of the time but not always..

An example.A woman drove off the right of way at the cottage. She asked me to pull her out of the mud. Her brand new car was down to the running boards all around. She was pissed at me when I explained It could damage her car.

She called in a tow truck. . Rather than lift the front end a little or at least cable from a high boom position for a more favorable pulling vector. He put a chain from his rear end and secured it to her car. Drove ahead and damaged her car. I do not know if the good Samaritan act or their being no cost if I had done it would have saved me from a potential legal issue had I helped her.

Agreed. Disconnecting the battery from a running engine, especially one as new and electronic as a '97 E300, could do serious and expensive electronic damage.

Unplugging the glow plug cable once the engine is running is a much safer test. Leave it unplugged until next starting the engine cold. Your mechanic should have a high-current meter that will detect if the glow plugs are still powered after several minutes of operation (past 'afterglow').

This could be just a coincidence with the break-in. Sorry to hear about the theft. Hope they got an empty backpack. In the future lock it in the trunk out of sight.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

It has been a long time ..... but I figured it out! Thanks for all the suggestions. I thought for sure it was the glow plugs sticking on but I ran a number of tests and I convinced myself that the glow system was working as designed. Additionally, since the car could be parked for a week and start right up I knew the problem wasn't a slow drain but a drain while the car was operating. So I hooked up my voltmeter to the + battery terminal in the engine compartment and the other end to ground and started the car. I watched the voltage vary as I turned on and off lights, the radio, accessories, and the like ..... and behold when I turned on the HVAC system the voltage dropped significantly from just under 14V to around 12.4V .... with everything running (headlights, radio, interior lights, etc) the voltage it would drop under 12V thus pulling battery voltage. So I figured I found the problem system. Next I disconnected the auxiliary fan at the radiator (it comes on with the AC) and ran the test again .... still the same low voltage. Next I disconnected the blower motor and my voltage remained at 14V .... so I knew that was the problem. When I removed the blower motor the black return wire was very hot ... and the motor itself was black as if it was burnt. I ordered up a replacement Behr blower motor and now all is well ..... problem solved.

Congrats. You win this week's Good Sleuth award.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970