My battery keeps going dead. I replaced the battery. I pulled the alternator and took it into Canadian Tire and had it tested, and it checks out as good. I put in a new alternator about 1.5 years ago, a bosch premium re-built. The belt tension seems good in that the alternator pulley is difficult to turn by hand.

The alt. belt had been squealing. Usually I could get it to stop squealing by turning off all electrics, like the heater, radio, seat warmers.

Any ideas??

The car is a 1989 420 SEL with 245,000 KM

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1989 420 SEL

Have you cleaned the inside surface if you battery terminals? If they have a corrsion built up then insufficient charge is reaching your battery causing it to periodicly go dead.

if not

It could be the voltage regulator built into the alternator. It can be replaced without changing the altinator and is a much cheaper fix.

also

You should increase the tension of your belt. (if required)

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Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra

Do you have an alarm system in your car?

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

I have only the factory installed alarm system in the car. I have no owner installed accessories in the car. All original equipment.

The battery terminals are clean. They have no corrosion on the outside or on the inside. I used one of those circular battery wire brushes.

I do have a spare voltage regulator. But shouldn't the defective regulator show the alternator test?

Any thoughts? Could it be the wiring harness? I see the positive wiring harness retails for about C$320, part number 126 540 25 30, which I would prefer avoiding. Maybe the juice is not getting from the alternator to the battery? I guess I could test it - check voltage at battery before starting, then start, check voltage at battery and at the B+ terminal of alternator. If B+ and positive battery terminal read different voltages, then the cable between the two is bad, especially if the battery is lower voltage than the voltage at the alternator b+. Right?

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1989 420 SEL

Put a DC voltmeter across the battery and see that it is putting out about 13.5 to 14.5 volts with engine running and reved up. Just because you replaced it, even if it was yesterday, you don't know if it's working right without checking it.

Hope this helps,

Boy is that the truth, I had to learn that the hard way!!

I replaced the alternator and charged-up the battery, before starting. After starting, at idle, the voltage across the battery terminals was 14.46v to 14.5v. Drove her 200km no problems.

The new alternator came with a pulley for 2 belts. I tried to put it on, but the old belt was too short. I took the pulley off the old alternator and put it onto the new alternator. The belt was tight, but went on with the help of a screw driver.

Thanks all for your help.

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1989 420 SEL

I agree,

Sounds like the voltage regulator. The brushes are probably worn out.

Just my 2 cents...

If Larry's advice checks out and you do happen to get the proper voltage output from the alternator, then it's time to see if you have a small electrical leak.

Disconnect the negative battery terminal and connect an ammeter that can read milliamps between the negative battery terminal and the cable clamp.

Watch the meter. You should get a reading below about 60 mA. If it is above 100 mA, you need to start pulling fuses to see which circuit is drawing the most power. Also, remove all the wires from the back of the alternator to determine if the alternator has a small leak.

When you find the culprit, the ammeter should get down below 60 mA, or about.

it also depends on the brand of the battery. DO NOT, i repeat DO NOT buy Everstart or Exide brand batteries for your Benz (any Mercedes). Any technician can tell you about past issues with these batteries. With Exide, after about two years, the battery starts to trap and collect all the sulfur on one side and ends up blowing up on its side due to heat and sulfur mixing together (slight heat from engine). With the Everstart, the battery simply sucks. It stresses on the label that it carries 875 ca, but that's only for about one month of use. What do u think the ca's will be in three months or one year? Definitly lower than half the original amount. That's where retailers like to get you by the neck and screw you over with the "warranty". So much for a 7 year warranty...

The only three brands that I can really depend on are Interstate, Duralast, and defintly DieHard (international).

I had one MB Tech tell me, around the first times I drove my 86' 300E, about that issue. I didnt believe him until my cousin ran into the problem with his 95' 500SL. It doesn't seem like a big deal, but it can possibly damage other electronics in your benz that require a certain amount of energy.

I would definitly look into that Cigar Havana...

Peace!
dj cee

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In Trance We Trust...

www.tranceaddict.com

Yours Truly,
DJ Cee

One other little thing: Check that your trunk light goes out. Switch goes bad and kills battery in one to two days. Nasty little bug to find. I found mine when I was checking my trunk seal for water leaks.