Battery weakens when engine's hot

[CNIXZGO]

This is what my z does, i get off the freeway after my 40 mile commute, stop to get a bite and park for like 5-7 mins. I come back out to start it up and she barely turns over. The engine is very warm, but not overheated. The battery eventually gets it to start but it sounds like it's ready to give out. Battery is about 18 months old, previous owner installed it. Does this ever happen to anyone??

P.S. When i come out to start it cold, it's fine!

[frank13]

Do you have a Digital volt meter or DVOM (digital Volt Ohm Meter)? Check the cranking voltage by probing the the Pos+ and Neg- terminals of the Battery with the volt meter (red +, black -) while cranking the engine over, disarm your ignition by disconnecting power to the distributor so it won't fire. Take a reading with the car dead, no key on doors closed, everything off. Whats the voltage. Crank 5-10 seconds, no longer. Note the voltage. A fully charged battery will read 12.60 Volts or higher. If you want to get a better reading turn on the headlights for a few seconds to get ride of the static charge from the battery then take the base reading. During cranking the voltage should not drop below 9.5 to 10 Volts for a computer controlled car. Usually anything below 9.5 to 9 volts and the computer doesn't want to work or the injectors want fire properly. Injectors are 12 Volt jobs. But it sounds like your starter is the actual cause for your "hot soak' condition. The heat from the engine increases the internal windings resistence of the starter solenoid. Either replace the starter or solenoid would fix this. Autozone can order the Solenoid Wells Part #ss314 $25.99(for example). Or you can Wrap the starter with a thermo wrap or fabricate a heatshield out of a piece tin/ thin gauge sheet metal. Also Before spending any money, check the battery post/cable condition. IS there any green/white/yellow fuzzy stuff any where? If so clean with tap water solution of baking soda and the water. This will nutralize the acid in the corrosive build up. Then remove the battery cables and clean them with a battery clamp/post cleaner. Clean both sides of the battery and the cables. Also where the cables bolt up to the starter solenoid and starter ear(ground -). Check voltage again. Did this fix the problem? If not try the heatshield. you can also pull the starter and walk it in to Autozone or Kragens. They will be able to check it on a bench machine that will give you amprage draw. Which is a measurment of the starters effeciency. If out of speck the starter is faulty. The heatshield/wrap is still a good idea. Hope this helps. :devious:

[CNIXZGO]

That's what most ppl are saying: sounds like the heat is causing the starter to go bad. Or at least making it starting to go bad. Thanks for the help! I might try the heat shield first. the battery cables are about a year old. starts great when cold.

[cruisingz]

if the starter and battery are ok, check your cables(both positive and ground wires). there is more resistance in the presence of heat, try maybe replacing both of them using a bigger gauge wire.

hope this helps

[GunnerRob]

I had the exact same thing happen to me, with three starters in a row.

It turned out that the parts store I bought the first starter from (the store replaced the other two under warranty) gave me the wrong starter. It turned out they were giving me a starter for a Datsun 4 cylinder engine! After I pointed out the difference (starter motor length) they gave me the correct unit and I've had no problems since. I'll try to get a measurement if you want it.

Good luck!:classic:

[280zx Fever]

i dont know if its been mentioned but...... stater motor solenoid could be on its way out :classic: good luck

[dogma420]

I'd say clean the battery terminals, and use a hammer when the car is in this situation and hit the selonoid a couple of times, this will unjam it and tell ya more.

[Daniel]

I would start with a good wire brush on all wire connections battery and starter. Hit the ground on the car as well as terminal. Perhaps heat=expansion enough to screw you up- cold=contraction/good enough connection. I am a believer in the hammer tap,its always got me home, But I tap the starter Not the solenoid. Solenoid is just a relay. Usually starter are brushes. On a stock 240 alt.The can easily be replaced on the car. Maybe your belt is loose.

[dogma420]

the hammer thing is for the selonoid. by definition it has a plunger in it, and it gets stuck. hammer when hitting the starter is actually losening the plunger in the selonoid. no effect on the starter itself.

[CNIXZGO]

Well almost 10 months after my original post, i found out it WAS the starter going out. Apparently the heat was weakening the starter. Had the solenoid and starter replaced and now it starts right up!!! Battery was fine. Luckily my starter decided to die right in front of my house! Had to have it towed in. Thanks for all the suggestions!