Help! Strange charging system symptoms. Bad alt.?

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Feb 12, 2014
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Gold Coast, QL, Australia
Symptom: washed engine - now alternator intermittently over charging, lights go bright and engine labours every 20secs or so when battery light comes on. Engine power loss under load.

I gave my engine bay a quick rinse down a couple of weeks ago, I've done this dozens of times before without an issue but this time I was heading away and the car wouldn't be started for another 5 days = cold sitting water.

When I came back my battery light was on and the engine sounded slightly labored like the alternator was working over time and I figured it will just be topping the battery up after sitting...
I took it for a drive and the light would go on and off but got less frequent, but now the engine would lose almost all power when under load like setting off from the lights and would take a few seconds to pick back up, which I had to be light on the throttle and fether the revs up. Revved out perfectly fine in neutral/park though.

The battery now showed red or 'replace' so I took it back under warranty but the multimeter test showed it to be fine.
They swapped it anyway and I just fit it but the car still intermittently shows the battery light (every 10-30secs) and when it comes on the engine drops revs a bit like it's laboring and the headlights and dash cluster lights brighten significantly, then back to normal again when the battery light goes off...

Could this random overcharging be a sign of a bad alternator? My guess is water could have sat in it for a few days and caused damage
 
In most cases the voltage regulator is part of the alternator.
So, YES, the alternator is bad and needs to be rebuilt.
Depending on the model/type of alternator, a good rebuilder can test it and see if it is just the regulator that needs replacement.
 
You might pull the electrical connector off the regulator and make sure there is no water in there, no corrosion or something messing up the works. Since it was sitting for 5 days, it may have possibly devloped corrosion in the connector if water was forced into it. Might even be worth de-pinning the connector and just checking to make sure.
This is why I dont wash engines ever. Too many electrical items and connectors that can get water trapped in them, more so if you are using a pressure washer, forcing the water into places it shouldnt be.
 
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