W123 240d not starting without jump
 

I trickle charged my car to a full battery over 48 hrs. I drove it ~20 miles (no radio/lights). I then let it sit for 4 days. I went to start it and it is trying to turn but never turns over. If i jump the car it turns over almost immediately. The battery is 6 months old. I disconnected the negative lead and used a 12v tester. There are no leaks to be shown. I first thought it was the glow plugs (3 years old) but when the car is being jumped it turns over immediately. I am very confused as to what to troubleshoot.

When you're jump-starting, are you connecting the negative jumper cable to the engine or to the negative post on the battery? If you're connecting to the engine block, I'd look at the engine-to-chassis ground strap and the chassis-to-battery negative strap. If everything looks fine, you might have the battery load-tested. Most auto parts stores will do it for free.

I attach it to the battery post directly

so after i trickle charge the car.. remove the charger... the car will start just fine. If i let the car sit for 4 days.... all the glow plugs will still activate, lights will come on.. and it will try to turn over.. but it will never turn. So it seems that the battery is draining (although with a 12v tester i don't see any pull on the battery when it's off).

Put a DC ammeter in series with your + battery cable and see how many mA you're running. If you have <50mA, have the battery load tested.

Charge the battery up. Start the car to prove the battery has charge. Disconnect one terminal of the battery. Let the car sit for a few days. Connect the terminal again. If it cranks well it is car related. If pretty much dead again it is the battery.

Personally I would not trust just charging the battery and testing It. You already know you can charge it up and it will crank the engine fine right away. At that time a battery tester may also show it as good. Making the test worthless. Unless repeating the battery check again in a few days after charging with the load tester.

good idea. i just tested the battery... voltage is fine (13v resting.. 14.1v running no load). I will unplug the negative lead on the battery and let the car sit for a few days.

i just plugged the battery back in and the car started fine.

I also tested the car by removing the negative lead and looking at the amp draw with the multimeter in series.

It seems to be drawing between 10-20 milliamps.

Not sure what else to look for at this point. I have replaced the dome light front and rear bulbs... beyond that... trying to figure out what else could be the issue.

Do a search on "parasitic drain". There is more info available than you will find from 1 thread.

You basically connect an ammeter or even 12 v test light between the negative battery post and the cable end. Begin pulling fuses until you find the one where the drain goes away. Note that some of the circuits are connected at the fuse box and the drain may go away when you pull the 2nd fuse.

Next test leave the battery hooked up but disable the glow plug circuit. There is a small chance the glow plug circuit is self energizing periodically. Just restore the glow plug circuit when starting the car and disable it right after the car has started.

You want to find the cause as quickly as possible. Drawing a battery down repeat times seems to damage them. Or shorten their service life. To me the modern car battery has low tolerance for being heavily discharged.

You could have a bad diode in the alternator that will run your battery down in short order, and you will not find it by pulling fuses. Easy test to do with a multi tester with the alternator in the car.

Yall are missing he did the drain test... 20ma...

What is battery voltage exactly? 13 is right off the charger.

First thing in morning after overnight sitting without charger running, what voltage EXACTLY is the battery.

12.75 is full.

Twenty milliamps drain is not a signifigant amount. At least not to me. That is why I suggested watching out for the glow plug system having some form of intermittent problem.

That 20 milli amps is a loss of about .5 amp per day. CCA cranking amps on your battery are going to be north of probably 600. So in a four day period a loss of two amps of the battery capacity should not be noticeable. This is only about 120th of the batteries current availability.

Generally if the diode pack in the alternator has developed some leakage This also is a pretty low value for it. That leakage will generally not be intermittent. Or increase and decrease. Diodes are fairly predictable. Also remember that aftermarket radios can have a light constant draw.

My suggestion of the glow plug circuit is a bit of a long shot. At the same time indications are you may have some form of intermittent issue when the car is inactive. These circuits can act up but usually have been missed by many posters initially when they did.

Many changed out the battery and alternator before finding the true cause of their current misery or mystery. [ no pun intended ]

when fully charged overnight the battery was sitting at 12.85v

car running without load voltage reads around 13.3-13.4. With load around 14v.


The glow plug system was upgraded 3 years ago to a manual push button. This is to eliminate any possibility of the glow plugs leaking due to that semi crappy glow plug module.


It has been running ok the past few days. I will post when it goes out again.

The battery i bought had a CCA rating of 850