Use your multimeter set to volts, test your battery with nothing turn on. It should be between 12.6 volts and 13.2 volts. Note the voltage (lets say 12.8 volts). Now start the car with everything turn off except the engine. The voltage should be higher than the base 12.8 volts. (14 ish) Now start turning everything on. Lights, blower, AC radio Note the voltage. If the power has not fallen all the way back to or below 12.8 then you alternator is outputting decent amps even at idle. If for some reason your car is idling very low the alternator may not be able to keep up but at normal idle speed it should

Good luck.

 

Volts with engine off - 12.4

Volts with engine on nothing running - 13.8

Volts with engine on stereo and ac on - 13.6.

Volts with engine on, stereo and ac and headlamps on high beam - 13.4

I noticed it drop to around 12.6 when the other fan kicked in, and then back to 13.4 when it turned off

Idles fine.

What do you reckon? Replace old battery?

Checked all inside lights and can't see any obvious drains. Everything is basically stock anyway except the stereo (stock speakers) just head unit changed.

 

bump

 

it sounds like the fan motor is drawing to many amps or alternator is not working as well as it should. does revving the engine change the volts when fan and stuff is on? i would take alternator and or fan motor in and have it tested at a local electrical shop.

 

I don't think its the fan as the voltage wont drop that low if I don't have head lights and stereo on, I guess it makes sense it be the alternator since mechanic has said battery is fine.


Will get the alternator tested and hope that's the issue... Then I have to try find the part here in New Zealand D:

 

for the boat we have a shop that does electric motors, starters and alternators and i can usually get fixed for way less than a new one. never tried taking an auto part in...