Originally Posted by Lohnes68
This is the 3rd alternator ive tried, its a bosch from Napa.
It charges 100% when the car is just idleing, no accessories on at all.
As soon as I start putting load on (lights, heater, heated seats) you can watch the voltage drop from 13.8 down to 12.4 or so, slowly. My battery charger indicates that the alternator is working at 0% and slowly drops the battery percentage as well. As soon as I turn OFF the accessories, voltage goes right back up to 13.8 and holds. Could there be something else wrong with the car other than the alternator thats makeing it do this?
Its a 2003 SL AWD.
If a voltmeter across the terminals of the battery right after starting the car shows 13.8V, then your alternator isn't working...or your battery isn't accepting the charge.
Normal alternator voltage output when cars are running is a bit above 14V. In the Murano I have learned that the voltage output from the alternator will drop below 14V while running if the battery is fully charged, but right after startup when you're calling on the battery to start and it needs to be recharged, I would expect to see at least 14V with a voltmeter on the battery terminals.
When you put a load on, the voltage should go UP, not down.
My conclusion: your alternator isn't charging....or if it's charging, it's only doing so partially....and if it's only charging partially, the cause could easily be a battery that won't accept a charge.
What I would do is charge the battery fully overnight (every garage should have a good battery charger, so get one if you don't have one) and check the voltage right after you pull the charger off. If it's under 12V, replace the battery - it's shot. After a charge, the battery MUST have more than 12V.
Drive the car 10 miles or so, park it and turn it off, then check the battery with a voltmeter again. If under 12V, replace the battery.
I'm not sure where the problem is, but if you've had the same battery through three alternators, I'm inclined to think the problem is not the alternator...and from this forum I've heard many, many stories indicating that Muranos are very sensitive to worn or degraded batteries.