2012 Honda pilot
Would a weak battery strain the alternator causing a whining on acceleration. Or is the alternator just going bad? Doesn’t whine sitting there just taking off, so under a load. Thought tranny but shifts perfectly fine up and down. No clunks fluid is good. 149k
Would a weak battery strain the alternator ...
Yes to this part.
... causing a whining on acceleration.
The strain and whine would be worst immediately after startup. But yes, increasing RPM could make it louder also if the bearings are shot.
is the alternator just going bad?
By the time an alternator starts making noise, then it needs replacing. But make sure it is actually the source of the problem, because other spinning parts can make noise too, such as power steering pumps, water pump etc.
A mechanic's stethoscope can help you pinpoint the source. You could also try unhooking the alternator.
Would a weak battery strain the alternator causing a whining on acceleration.
Not likely. Why not load test your battery and alternator if you suspect that? You could use a mechanic's stethoscope to listen for noise under the hood. There are a number of possibilities, including any belt-driven accessory or pulley.
Thought tranny but shifts perfectly fine up and down. No clunks fluid is good.
That's irrelevant as to whether it's making noise or not. Has the transmission been serviced regularly over the last 13 years? At 149K the fluid and filter (if applicable) should have been changed at least a couple of times by now.
Since noises can telegraph all over a vehicle you might want to use a noise-finding device like the ones Scotty has demonstrated to zero in on the culprit if not found under the hood.
@chucktobias I’ve had the vehicle for 5 years and from 114k. I have done two drain and fills. Before that unsure. But fluid is full and looks ok
Most likely OK, you'll want to eliminate belt-driven items under the hood first. I would suspect a worn pulley more than the alternator, but the alternator is a possibility. A quick check would be to run the engine briefly without the fan belt and see if noise goes away. If it does, you know it's something belt-driven and can zero in on it from there.
@chucktobias ok I don’t hear it at idle or in p or n. If in drive and foot on brake and rev I don’t really hear it either maybe a little but hard to tell
A mechanic's stethoscope may pick up sounds that you don't hear otherwise. Also you can load test your battery and alternator to check their health. I would probably do that first since it's the simplest and you'll want to rule out (or confirm) those problems first.