intermintant slow crank dead battery

[95se]

I have tested my battery, alternator, starter. Every now and then it acts like the battery is dead but i jump it and its fine for weeks. I have cleaned all postives and grounds tested every wire for shorts and corrosion and found nothing. I think its corrosion in the fuse box or a dead spot in the starter, any thoughts guys?

[Plemmons]

Have you tried having it tested for a parasitic drain? This can be tested at your local advance auto parts, as part of the system test (battery, alternator, starter, as you said). If there's nothing pulling your battery down and you've verified that the battery itself and the cabling is good, you can remove the starter and have it bench tested, if that's what you suspect. Unless you have a case of disappearing coolant: engine coolant in the cylinders can cause a slow cranking situation, as coolant is not combustible and does not easily compress. I think it's called "hydro-lock". I don't think the problem would show up intermittently, though. Hope this helps!

[95se]

I am a mechanic myself, i have also tested for parasitic drain and have no leaking injector and also bench tested my starter last night. This is why i am lost i covered all of my bases... as noted

[RJolly87]

There is one word that you used that will absolutely be your undoing: Intermittent.

Intermittent is always a PITA to track down.

My suggestion would be to study the issue more, and learn more about it. Is it actually low voltage when you come to it? Is the voltage fine until you hit the key? Things like this. A digital voltmeter may go a very long way to help track it down. Once you have a better idea on the tendencies, then that can help you narrow it down.

[95se]

I have used my volt meter when it does act up and it drops somewhere in the 8.7 range while cranking but when not cranking it goes back up to about 11.6 where it should be. Its acting as though the engine totally locked up and it cant turn it over. That is why im thing its a dead spot in the brushes on the starter becuase that would create a load that the starter cannot turn

[AJT2004]

Sounds like a weak battery. Did you load test the battery? A simple volt test does not prove a battery is good. For testing the battery needs to be fully charged before the load test. I don't think 11.6 volts at rest is good, should be about 12.3 with the ignition off.

[95se]

11.4-11.6 is what a battery is normally charged at, a 12 volt auto battery is never really at 12 volts at rest. 10.6v is the lowest rest voltage that it should start at, lower than 10.6v and it wont start. But that is not my case as stated. and yes i have load tested the battery.

[AJT2004]

Although a weak battery may not be cause of your problem it is not correct that a fully charged 12 volt battery is less than 12 volts a rest.

It's 12.6 because each cell is 2.1 volts.

If the battery is

12.5 = 85% charged
12.4 = 65%
12.3 = 50%
12.2 = 35%
12.1 = drained

[RJolly87]

11.4-11.6 is what a battery is normally charged at, a 12 volt auto battery is never really at 12 volts at rest. 10.6v is the lowest rest voltage that it should start at, lower than 10.6v and it wont start. But that is not my case as stated. and yes i have load tested the battery.

This is also assuming a battery in good health. The lowest voltage I have seen on mine was 11.9, and that was with engine running, after commuting with a dead alternator. My first guess is corrosion on the cables, but if something is locking the engine so much so that it won't turn without extra voltage, there would be signs of that even when starting and after starting.

When it's jump started, does it start right up, or does it still fight the first couple of cranks?

[AJT2004]

The required voltage is only part of the story- the amps are the "power" to crank an engine. A bad battery can still show 12.6 volts. I think this may be a combination of a weak battery and resistance/corrosion at the cables. The two nested positive cables need to come apart as well. The starter could also still be suspect although you performed a bench test. Is it the orginal starter? if yes, I would consider replacing it.

[Plemmons]

@AJT agreed. A defective battery can still show 12.6V and not be worth anything. I see it all the time... Here's one thing to try: take a measurement of the CCA, trickle charge the battery until it completes a full charging cycle and then take another measurement. If it shows 12.6V and the CCAs that it should, I would eliminate it as the root cause of the issue. If it doesn't come up much and still shows lower than the specified CCAs, the battery is likely at fault, even if it will start the car after.