on/off starting

[riverrunner]

Hey All,hoping for some insight into a starting mystery,We have a 1999 NB 1.8t.every month or so car will not start without external help,in this case a portable jump starter.after starting it will be fine for a month or two,there are no other problems with electrical we are aware of.I have had starting system checked by reliable mechanic to include alternator and battery.any info will be greately appreciated.Thanks in advance.

[red99]

Is your alternator original? If so, it could be worn brushes. Alternators need to have a current source to operate since the field magnet is an electromagnet. Normally some of the current generated by the alternator is fed back to run the electromagnet. If the brushes become intermittent, then the current to the electromagnet is interrupted and the alternator effectively shuts off. It will work again just fine when the car is restarted until the brushes interrupt once more. So a failure mode can be that the alternator works fine 99% of the time, but once in a while the battery runs down when the alternator has shut itself off. On these alternators the voltage regulator/brush assembly can be replaced so you wouldn't need to buy the whole alternator. The brush assembly is around $60.

[riverrunner]

Thanks I appreciate your reply,I have a couple of ?s how do you determine if is OEM,and is this something that the average person can do? Are their any tests you can perform with alt in car or does it have to be removed.thanks again PS I showed this to my wife and she thinks it makes perfect sense.

[red99]

The original ones have a VW logo in white paint near the battery cable connection.

A few more questions:

Does the drained battery only happen after sitting overnight, or can it happen anytime?

Have you seen the generator light come on while you are driving?

How old is the battery?

[esse10]

Check under the battery tray for the grounding chassis connection (negative wire coming from battery) it tends to get very corrosive and looses continuity and electrical starting problems, especially old cars. check out the pictures on what I found in the thread titled CAUTION in the 1.8T section. Good luck.

[riverrunner]

Originally Posted by red99

The original ones have a VW logo in white paint near the battery cable connection.

A few more questions:

Does the drained battery only happen after sitting overnight, or can it happen anytime?

Have you seen the generator light come on while you are driving?

How old is the battery?

Yes to # 1

No to #2

About 1yr old battery.

[riverrunner]

Originally Posted by esse10

Check under the battery tray for the grounding chassis connection (negative wire coming from battery) it tends to get very corrosive and looses continuity and electrical starting problems, especially old cars. check out the pictures on what I found in the thread titled CAUTION in the 1.8T section. Good luck.

Thanks for the info we will check both items

[red99]

If it only happens after sitting overnight then there is probably something on in the car that is draining the battery. The alternator fault would light the "generator" light and the battery could drain while you are driving. These "parasitic drains" as they are called are fairly common. Sounds like you have something intermittent like a rear hatch leaving the luggage light on. Have you added any electrical accessories to the car?

[riverrunner]

nothing added to cars electrical system,if it is a drain on system their should be someway to find and fix.it was -10 yesterday and we were trying to jump start, wife likes car but is ready to get rid of.since purchasing I have put over 2,000 in motor and hate to give up on it but might be time to move on.Thanks for all input received.

[red99]

You can check for a drain on the system by disconnecting the negative battery terminal and connecting an ammeter between the terminal and connector. Be sure ignition is off, doors closed, ect. There should be <100mA current flow. If there is more, disconnect fuses one at a time until you find the problem. From what I've found it is usually the fuse for the interior lights, which I believe also has the comfort module.

Also check the battery voltage immediately after starting (within 1-2 minutes). It should go up above 14 volts while the battery is charging. Less could indicate the alternator brushes. How many miles are on the car? Did you check to see if the alternator is original?

[riverrunner]

I will do test you suggested this weekend,battery was charged last night and is starting today.when doing test and you do locate a particular area that is drawing power how would you isolate the problem area? I have not checked alternator as yet will check this wknd.appreciate you staying on this,thank you

[red99]

Assuming you do have excessive drain and are able to isolate it to one fuse, then you can use the info about what is on that fuse to isolate further, unplugging components one at a time.

[riverrunner]

Into garage tonight and try to find problem,thanks again for taking time to help.

[riverrunner]

Update on what I found regarding our sporadic starting problem.# 1 distribution panel on top of battery has melted fuse holder for cooling fans,someone had bypassed this and installed a inline fuse,#2 panel cover was fused to cable going to alternator.so at this point I am not sure on plan of action as costs to repair will probably be more than I want to put into car.thanks again for information received.

[red99]

Originally Posted by riverrunner

Update on what I found regarding our sporadic starting problem.# 1 distribution panel on top of battery has melted fuse holder for cooling fans,someone had bypassed this and installed a inline fuse,#2 panel cover was fused to cable going to alternator.so at this point I am not sure on plan of action as costs to repair will probably be more than I want to put into car.thanks again for information received.

Fuse panel problems are common. Replacements are available:

Volkswagen New Beetle 2.0 > Engine > Electrical > Fuse Panel > ES#2539371 Battery Mounted Fuse Panel - 1C0937617

[esse10]

fyi-Yea but you still need to find out what caused it to melt like that. The problem will come back if you don't find the root of the problem. good luck man

[red99]

Originally Posted by esse10

fyi-Yea but you still need to find out what caused it to melt like that. The problem will come back if you don't find the root of the problem. good luck man

The problem is simply a loose and/or corroded connection on those fuses. The heat generated at a connection is equal to the square of the current times the resistance. So if you have 100 amps coming out of the alternator through that large fuse and even just 1/100 ohm of resistance that is 100 watts of heat. That is plenty of heat to melt the plastic even though the fuse remains intact.

[IndyTom]

Originally Posted by riverrunner

Update on what I found regarding our sporadic starting problem.# 1 distribution panel on top of battery has melted fuse holder for cooling fans,someone had bypassed this and installed a inline fuse,#2 panel cover was fused to cable going to alternator.so at this point I am not sure on plan of action as costs to repair will probably be more than I want to put into car.thanks again for information received.

Just replace the fuse box on top of the battery and you should be good to go. Not too expensive and fairly easy to do.

[esse10]

Originally Posted by red99

The problem is simply a loose and/or corroded connection on those fuses. The heat generated at a connection is equal to the square of the current times the resistance. So if you have 100 amps coming out of the alternator through that large fuse and even just 1/100 ohm of resistance that is 100 watts of heat. That is plenty of heat to melt the plastic even though the fuse remains intact.

Hey thanks for the basic lesson in electrical formulas, it almost took me back to grade school for a moment there LOL

[riverrunner]

I considered replacing the panel but not sure this would solve problem,there must be reason this happened,I turned fans by hand and they seem to be operating OK,my concern is cable to alternator being hot enough to fuse to panel cover and melted fuse holder.I would prefer to have problem fixed but not sure I want to keep putting money in lost cause.Since purchasing I have replaced timing belt,water pump,all tensioners,plugs,cabin air filter,flushed brakes,installed new mud flaps,serpentine belt and numerous cosmetic items.I have no problem investing more money if it fixes problem,car runs great and looks good but this not starting problem is changing mind.