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93' W124 E36 AMG ; 71' Cadillac Eldorado ; 07' S211 280 CDI
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Discussion Starter #1
Winter has already struck over here and a major problem reappeared in my 250D.

Every now and then You can find that the battery is dead.

The most annoying thing is that it doesn't happen all the time.

When it's warm the car runs fine, but when it gets cold the issues appear.

I searched for any trace of possible drain and found nothing. Apart from the clock obviously...

The alternator had the voltage regulator changed to the "biggest" one and it's pumping over 14V on fast idle with the main lights on.

The battery is 2 years old Varta 74Ah. It has been load tested several times over the last two months to make sure that it's not the battery.

I am slowly running out of ideas.

Some users claim that a bad OVP can cause an intermittant drain. Is it possible?

I noticed that one of the threads on the rear glass doesn't heat anymore. I wonder if it can actually take so much power that the alternator is not able to charge the battery? It has a fuse for crying out loud.

Finally - is it possible that the alterantor is charging the battery with 14V with the main lights on, but when it's cold and I use more power consuming stuff, it is just not able to recharge the battery?

Is there anything that can come on with the engine off, that is temperature sensitive?

Any input will be much appreciated.

Maciej
 

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2013 E350 sedan, 2013 E350 cab, 1993 400E sold,1999 ML320
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2,436 Posts
14 volts at idle is high with lights on. Id say 13, maybe your battery is losing water by being overcharged. Batteries work better when warm thats why they have a cca rating. Even maintenence free batteries have a hole in which to add water if its being boiled off just harder to do. I would check that regulator again tho.

The door lock system can have a leak when colder out and pump can run longer and draw the battery, mine does.

Also how far are you driving? time driven not idle is what you gage to charge battery. If your not driving like about 20 minutes at least your not actually charging the battery.

Also if your battery has been drawn totally down a few times the cells inside could be going bad now and may just need a new battery. Remember cold and setting a battery on concrete are the 2 worst things for it. The plates inside fall apart then you get what they call bad cells. Hope I gave you some ideas.
 

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93' W124 E36 AMG ; 71' Cadillac Eldorado ; 07' S211 280 CDI
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Discussion Starter #4
The door locking system would be my guess then. Only - how do I track the leak? If I park in garage - it will be too warm. It never fails to start, when parked in garage.

The problem is - this car has to be parked outside and I have no alternative but to find the culprit and fix it.

Why would the locking system have a leak when colder? Material shrinking? What are the most common locations for vacuum leaks in the closing system? I have been tracking a vacuum leak in the other system (lights/idle etc.) for years and haven\t been able to find it...
 

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93' W124 E36 AMG ; 71' Cadillac Eldorado ; 07' S211 280 CDI
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Discussion Starter #5 (Edited)
What do You mean by specific symptom? The car starts fine after recharging the battery externally but after a night out in the cold it will not crank.

When we started the car using a battery from another car, then switched the batteries and drove 100km - it started without any problems on the end of the trip. Next morning - no crank.


Actually it's not always true - sometimes it takes 3 or 4 days for it to go dead and sometimes it's one night of -15C.

I am curently looking for a new OVP for it.

The problem never occurs in summer. Only when it gets cold. I happened a few times last year, but we just let it sit for a season and started using it again in summer. This year it really needs to be going strong, so I need to find the source of the problem.
 

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93' W124 E36 AMG ; 71' Cadillac Eldorado ; 07' S211 280 CDI
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Discussion Starter #6
Anyway. If the problem is caused by the closing system vacuum pump - it should go away if I disconnect power to the pump - is that correct?

And if the problem is caused by the OVP - it should go away if I disconnect the OVP - right?

I guess I will disconnect the central locking electrical pump and see what happens after the next few nights. If the problem goes away, I will have to examine the closing vacuum system closely or disconnect it and live without it until I can fix it. If the problem remains, I'll do the same with OVP.

What do You think?
 

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99 SLK230 Kompressor, 5 Speed Manual
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1,117 Posts
Okay, here's what I suggest:

Start by verifying that it is INDEED a charging problem. Rig up a voltmeter with wires to the the battery with the meter temporarily in the car. Monitor the charging voltage a few days. If it constantly stays between 13.5 to 14.5 or so while engine is running, it's time to move onto searching for a drain. If the charge voltage does indeed turn out to be intermittent. Thoroughly inspect alternator to battery wiring and possibly replace the alternator. I don't remember ever seeing an alternator intermittent, but if deep grooves are worn in the rotor, even a new VR can end up being flaky.

To check for a battery drain, Use a 10AMP Ammeter. Remove a battery cable and put the Ammeter in series with the removed battery cable and the battery post. If it is showing more than about 100 milliAmps, start removing fuses one at a time and check for the current to drop after each removal. When you remove a fuse and the current decreases, that's your leaking circuit. If you go through all the fuses and still have a drain, you will have to procure and study a wiring diagram to determine other circuits that are not the normally fused circuits.

Hope this helps.
 

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93' W124 E36 AMG ; 71' Cadillac Eldorado ; 07' S211 280 CDI
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Discussion Starter #8
^^

It's always good to refresh the standard procedure...

Nevertheless I'd not start a new thread if it was something like that.

The alternator is fine. The voltage on the battery with the engine running is always higher than 14v. We use high voltage regulators here due to the fact that we are obliged by law to drive with our lights on all year round. I am sure the battery isn't overcharged.

The drain, as indicated by my multimeter is 0.00-0.01A. It actually goes to 0.00 when I disconnect the clock. That's it. If the car stands in warm - no problem. Let it stand some time out in the cold and You won't be able start it.

It must be a drain, which occurs only when it's cold. Since the central locking system pump turns itself on intermittently if there's a leak in the system - that would the most probable cause of problems.

Before I start looking for an air leak (which is a B**** to find) I'll disconnect the pump and leave it for a few nights to see what happens.
 

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99 SLK230 Kompressor, 5 Speed Manual
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1,117 Posts
Okay, that gives me more info. If you already posted this info and I missed it when quickly perusing the thread, I apologize.

There is NOTHING worse to troubleshoot than an intermittent problem. I would rather something smoke, then it's easy to find.

Have you already cleaned and verified battery terminal connections and grounds? The reason I ask this is that if you have a flaky connection, you can have a hot battery but still no or slow starter.

This might be a tough one, but it sounds like you are analyzing it in the right way. The 10 milliAmps draw that you measured is nothing at all to worry about.

I'm sorry I don't have anything more to offer.
 

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89 300E; 00 E320
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Is there anything that can come on with the engine off, that is temperature sensitive?
The only thing I see with a temperature sensor in the charging system or power distribution is the preglow relay and it has a transistor for what that's worth. It is kind of confusing because it has a couple of hot all times and hot in run or start inputs. Maybe there is another one somewhere too.

You will see the OVP in these diagrams along with other components and relays which draw power and with the starter being most closely connected to the battery in the charging system diagram.

Preglow System 112

N14 Preglow time-limit relay Left side of engine compartment, on inner fender

Charging system

Power Distribution 105-1 106
 

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Okay you confirmed that the problem exists with a different battery; that was where I was heading.

How about installing a cutoff switch at the battery so you can disconnect power at night. The battery should be fresh every morning if you followed this process. You could do this for a few days to see if it has an impact on the problem.
 

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93' W124 E36 AMG ; 71' Cadillac Eldorado ; 07' S211 280 CDI
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Discussion Starter #12
I disconnected the closing system pump and the OVP relay. No ABS, no power locks, but after a night outside there was 12,65V on the battery. I will leave it like that again tonight. If there will be no drop in voltage, I'll connect the OVP and see what happens.

How is it possible that the locking system pump can come on when the car is closed? I don't quite understand. If it's locked, then it's locked. Why would the pump struggle to maintain the pressure?
 
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