How many Volts is too low to move starter?

[JP911]

I just started having starting / electrical problems where when I turn the key all of the power comes on inside the car, but the starter doesn't make a sound. The voltage on the battery was at 11.5 volts. When I jump start it the car fires up on the first try. My battery is a 6-month-old Optima (red top)and I checked for draws on the battery with an ammeter and there is nothing out of the ordinary. I checked the volts on the battery with the car running and it's at 14.5, so the alternator is charging OK. What should I do next?
Thanks,
Jon

P.S. I did do a search, but didn't turn up much beyond what I've already tried.

[Rot 911]

11.5 before or during starting? If before starting you have a bad battery or one that is grossly undercharged.

[JP911]

11.5 is before starting (jump starting), but should the starter still "move" with that voltage?

[Rot 911]

Originally posted by JP911
11.5 is before starting (jump starting), but should the starter still "move" with that voltage?

Probably not unless you charge the battery back up. Just jump starting might not do it.

[RoninLB]

Optima can be a pain to recharge.
I usually do the high amps/start switch till the charger needle drops to about 10amps.. then the slow recharge and wait about 1hr after the needle gets to 2amps

[Joe Bob]

Good be bad grounds as well....best to have the battery load tested to see if it has a bad cell or two......if it tests out OK...start cleaning corrosion.

[JP911]

Mike-
Where exactly should I start cleaning corrosion? Sorry for the idiot question, but I'm not all that up-to-speed on matters electrical.

[oneblueyedog]

Oh no. Another starter circuit gremlin thread. I'm following along with this one as I have not solved mine completely.

I'm to the point of running an extra yellow jumper wire to the solenoid.

Check out a seach on this subject. I've done everything except the jumper.

[aigel]

I just took that rigged 'hot' start solenoid off my starter. You can have it for shipping. It is a crutch. If you have a good starter and all good contacts, you should not need a hot start relay on top of the relay ...

11.5, that's an empty battery, dude. That would probably not move any of our starters either. Stick in another battery from someone else's car, just so you can see the difference.

George

[Joe Bob]

First check the battery...then check grounds.....when cleaned up and with a fully charged batery it should read 12.5+ volts.

Grounds include the one on the trans that connects to the chassis.

[amk]

Yep, bad battery. 11.5 will not turn the starter on mine.

I had a similar problem a few months back, it's puzzling at first 'cos the battery is not dead, it has enough juice for lights and stereo, just not enough to start the motor. I bought a new battery and it's been fine since.

[masraum]

11.5 is not fully charged, it may or may not move the starter. You need 12.5 to really know for sure, but it's not really the volts that do the trick, it's the amps. You can have a battery that is charged to 12.6 volts that won't even light the dome light. Without the proper charge there's no way to tell for sure if you have the amps necessary to turn the thing over.

[RoninLB]

removing the "surface charge" after recharging gives a better picture of condition

[911pcars]

As a point of reference; if the battery dips below 9 volts when cranking, most shops call it discharged. Could be discharged or large paper weight. Most batteries must start out at 12.9 - 13.2 voltsand be fully charged to meet this requirement.

The only way to tell if the battery is toast or merely discharged is to trickle charge it until it's at full charge. If it's an open cell type, use a hydrometer to verify. If it's sealed, charge for at least 24 hours before testing. Battery testers usually apply a load on the battery to simulate cranking the engine. If the battery stays above 9 volts for approx. 15-20 seconds, it's usually okay.

The latest electronic battery testers can actually test a battery under any state of charge to see if it's okay.

Sherwood

[singpilot]

I have found that the minimum volts to turn the starter is the square root of the compression of just the highest cylinder minus one half of the ambient temperature in degrees F.

Will sometimes be adjsuted for variables like an Optima on sale at WalMart.

[RoninLB]

Originally posted by singpilot
Will sometimes be adjsuted for variables like an Optima on sale at WalMart.

exactly what I was trying to convey in my previous reply.. thanks.

"Optima can be a pain to recharge.
I usually do the high amps/start switch till the charger needle drops to about 10amps.. then the slow recharge and wait about 1hr after the needle gets to 2amps"

[911pcars]

"Optima can be a pain to recharge."

I agree. The best plan is to use a battery maintainer when it sits so it never gets to that threshold.

Sherwood
same Optima since '96 (knock on wood)