jwillman

Will the auto store " we test your alternator" adequately evlauate the health of the 928 alternator? Think mine has issues at high temperatures since cold start shows 13.8 to 14v when cold and much less when hot.

Car is without the cooling shroud and hose!

GlenL

It's a regular alternator.

Is that a external voltage measurement? Always check charging issues with good voltmeter instead of the dash gauge.

depami

Which means maybe, maybe not. Depends on who's working. They will likely have the proper equiptment but no one that knows how to properly use it.

I am lucky to have a place within 20 miles that specializes in auto electrics. They have often done repairs while I wait.

http://www.wenzelautoelectric.com/

Definately the only way!

jwillman

Thats a digital VM connected at the battery cables.

depami

Check it at the alternator to eliminate cable / connection losses.

That should be relatively easy without the cooling shroud.

WallyP

Standard practice is for the voltage regulator to lower output voltage as the temperature goes up. The idea is that the battery is also getting hotter, and thus needs less voltage to fully charge. In your case, you are "cooling" the alternator with air that passed thru the AC condenser, then the radiator, then over the (very hot) exhaust manifold.

My auto electrical rebuilder has told me that he can special order a regulator that has less voltage drop with increased temperature, and I plan to do this when/if I get a 928 alternator rebuilt.

tmpusfugit

Jim, generally speaking the test done at the usual auto stores with their on counter tester is at best marginal. I usually try them out, but I have had bad alternators test good, and good alternators test bad at both Advanced Auto and O'Reilly's. Given your symptoms I would not expect their test to find the real problem, unless it is very obvious and heat over time and load over time is not part of their test. As others have suggested what you are seeing is more or less common, to maybe a lesser degreee than than you are seeing.

I know you have been deep into your car many times, more so than most of us...but, I would suspect the alternator wires where they come off the alternator and travel up to the harness as being either corroded or have broken strands, or possibly my old favorite, a poor ground cable from the battery to the frame...those have been beat to death on other threads with other symptoms...but I had one crap out last month, I had a digital VM plugged into the lighter socket (Radio Shack sells a cheap adapter that allows that) and I was showing a larger drop from cold to hot than I liked. After the cable completely failed and I put on a new one the DVM showed about .3VDC higher when hot than it had been showing before the failure....that suggests I was heating up the ground cable more than I was charging the battery....YMMV

jej3

Sounds normal to me.... rolling around in the cool mountain air @ SITM, my dash gauge was at or above 14 the entire time. Rolling around in hot, sweaty Florida, I am at or below 13, less in traffic.

I think you'd be better off finding a ghost than having the local autoparts franchise tell you you're normal or the voltage output is temperature related.

jwillman

Thanks all.

Jim,

I have already replaced the battery ground but need to look at the alternator connections / wiring.

The AC Delco mod looks better all the time as it incorporates the more modern electronics Wally mentions as well as a bit more power.

Fontana

I just went through this a few days ago. I took my alternator to a local Autozone and it passed all 3 tests. I was not confident with the testing abilities of the counter person as he was not confident that the connectors were correct for proper testing. Feeling unsure, I went to Advanced Auto, where my Alternator passed 2 out of 3 tests ( their testing method/hookup was different than Autozone). The one which failed was the Stator test. After that, I went to another Autozone right across the street and it passed all 3 tests.

Uncertain at this point, I found out there was an ignitiion specialist nearby who completely rebuilt my 115 amp stock Bosch alternator while I waited for $95, bearings, all new copper, sandblasted and all. He was very honesty and swore the alternator was not responsible for my charging problem, but said it needed new bearings, so I said while he had it open to just rebuild it completely. I had it done for extra long term insurance. Long story short, find an ignition specialist rather than the auto chains, they can just add to the confusion...

danglerb

Today the alt in our Lincoln died, no indication (which seems REAL) odd, started fine after filling with gas, stopped to pick up a sandwich for my son, would not even turn over. AAA now includes battery service, so the guy had one of the new fancy electrical testers (guessing maybe a midtronics) which does a "fair" systems test and prints out the results.

Not saying the testers are idiot proof, those have constant updates, but its close, and fast.

If I have some charge on the battery, not totally dead, and the voltage at the battery isn't over 14v at 1500 rpm or so, and no special loads like the electric fan, pretty sure the alt is toast.