I think I spoke too soon (alternator)

[leapdragon]

Hi all,


So I recently preventatively replaced my 205k original alternator (2007 XC70) preventatively with a Bosch reman (from Bosch).

I *thought* everything was just fine, BUT... When I fire up Torque, the CM voltage is reading 13.5 at idle from the new reman, and drops to 13.4 with all accessories powered up, whereas it was 13.8 at idle on the old unit. dropping maybe to 13.7 with all accessories powered up. And the reman seems not to want to get above about 13.8 no matter what (i.e. at speed), while the old would would hover around 14 at speed.

When I power down, battery voltage w/car off seems to be around 12.4-12.5 volts. Doesn't *seem* to be declining across trips...

Am I overreacting here, or do I need to grudgingly put the old one back in and send the reman back to Bosch?

Also, I did specifically buy the 2006-2007 part #, but this sounds a lot like the problem that people have described with the incorrect year voltage regulator... Is it possible that it's got the wrong regulator in it anyway?

Also #2, complicating factor, it is well over 100 degrees F outside right now as I am testing this (I believe 104ish), which wasn't the case days ago the last time I checked the old alternator voltage, and there seems to be some suggesting that voltages are expected to be lower in heat. How true is that?

Of course, my Vida installation (which lives in a VM) seems to lock up the VM right now so I'm going to have to rebuild it, but I'll need to solve any alternator problem before I dig into that.

Any advice appreciated before I dig back in tomorrow and swap alternators out (again).

[jonesg]

I'd leave things alone.

[leapdragon]

Interesting you say that, turns out I lied before, I did in fact set up VIDA again this evening (this time on an old laptop, not in a VM on a Macbook, hopefully that makes it less finicky).

Ran the quick alternator test and it passed, though not in a way that inspires confidence—VIDA instructs you to first turn off all the loads, then gives you an "ok" range (mine is in the low 20% of the range at all times), which is the opposite of the way I'm used to thinking about testing alternators (turn all the loads on, see if you still get at least ~14v at idle). But it did walk through the temperature ranges and get the alternator up to 14.6v or so in the super colds, so I know it can do that voltage now, even if I don't get to see it in Torque.

I also ran the manual alternator test in VIDA (which shows the current battery temp) and CEM battery temp shown was 38c at 2:00 am (yup, sitting in my driveway with VIDA at 2:00 am), which I suppose explains the lower voltages.

I guess I leave it alone for now, watch it, and set about having the core I pulled out rebuilt just in case.

But now I have a question: is there really a battery temperature sensor in an '07 XC70? I can't remember ever seeing one in any of my XC70s (this is my third), and I can't seem to find battery temperature sensor as a part. Is this temp being inferred from something else? If so, any way to hack it? I'd love to boost the alternator charge voltage to the *upper* 50% of the range with resistor or some such if anyone has ideas...

[dikidera]

My experience is that the apps lie sort of. Depends on the dongle.

[leapdragon]

So this morning the difference between old and new kept nagging at me and my mind went back to a particular moment during replacement—when I'd eyeballed the pigtail and the nut and they looked "pretty good" and then I'd bolted them on.

I tore back into things, took off the nut and the pigtail (which still looked "pretty good") and gave them a good polish with a Dremel polishing wheel and some diamond paste that I keep around for completely separate hobby purposes. Got them good and shiny and clean. Brake cleaner, wipe down, bolt back together. Try again.

Voila—0.3v higher across the board. They looked fine, but they weren't. And with a 0.3v drop, that's excess heat and load over time, potentially some long-term arcing damage, etc.

Lessons learned:

(1) If something's nagging at you, dig into it.

(2) Don't skip the basics. Clean, clean, clean your connectors whenever you have them apart, even if they look "pretty good." I feel foolish. But hopefully this is now fixed. I'll follow up if that turns out not to be the case.

[abscate]

When you are dealing with primary wiring, battery, alternator, starters, yes-you need a new standard of clean on those high current carrying connections. Dremel is your friend there.

Voltmeter is your diagnostic friend. With everything off, you don’t want to see even 0.1V difference between battery and connector. Once it’s running 100 Amps current , any resistance will make it futile

[jimmy57]

The P2 does not use a battery temp sensor but does use ambient and does some computing for battery temp gain. The charging voltage is lower for higher ambient. The post at underhood fuse/relay box is known for loss that you have now fixed.