11.9 is close to 12v
whats the problem if 12v from battery are just needed to start the car
if it happens when running
what are the symptoms?

Just FYI, I have had my 90 GSX without heat shields on the O2 housing for 9 years and I have put 6 Alternators on it. The un-shielded O2 housing will cook the bejesus out of the alternator and 4 out of 6 times the result for me was a low voltage reading before it stopped working altogether. Also a healthy alternator will normally output 12-14 volts, 11.9 is low unless there is a high draw.

yes that does seem low and yes best to keep the heat away from that alternator the high temps will be no good and toast the alternator

The biggest place you need to worry about your voltage drop is your fuel pump. Measure what your voltage is as close to the pump as possible. A good rewire will cure that. I've seen 11.x at the fuel pump at WOT with a shitty inline fuse and 10ga wire from battery to pump. Put in a good 8ga. rewire with a good, quality inline fuse holder, and I've seen my voltage get as high as 13.9V 3" away from the fuel sending unit. That's where you need to be most concerned. DSM charging/electrical systems suck horribly when it comes to voltage losses.

It is my car. The issue is it dips volts under WOT. Sometimes as low as low 11's to high 10's.

Did you ever get that heat shield back on?

Hi!
I have a similar problem. When cold motor voltage 13,5-13,8V. After warming up the voltage drops to 12.8 and 12.5, ie below the battery. I thought that my alternator overheats. I moved it to the place of the air conditioning compressor. Result - 0! nothing has changed. This is my third alternator.
Measure the voltage on the battery spend.
Any suggestions please!

Like how this thread managed to jump around from 2011 to 2014 in a short time.

Going through alternators? Bad battery that can't hold a decent charge, or cruddy battery connectors are the usual culprits in this situation.

The battery is what runs our system and the alternator is the "ballast" that keeps the system in check. If the battery isn't performing as it should, then the alternator had to do all of the "dirty work", and the alternator isn't designed to do ALL of the "dirty work" needed. If it does, the regulator lets go and this causes the alternator tol not act as the needed "ballast" the battery needs....and the system begins to fail.

Get a new battery, or get new battery connectors, or at least clean up the connectors to metal bright and all wires attached, and metal bright clean to the connectors, are rock solid tight.

I've had my DSM for over 6 years and still on my first alternator.

Today alternator put on the stand and gave load 50A. He worked for 5 minutes, began strongly bask and fall voltage 12,9V. It turns coil (outer) stator start whiling away. And this is manifested only when the generator is running at least 5 minutes with a good load.
Winding has a lot of rust quickly fail because I do not have the side cover of the engine on the left (she Uther MB528711). Water from under the wheels when turning in the right, falls exactly on the alternator and its belt.

I went thru alt with an issue like this turned out to be ground related