Was having some alternator troubles. My wife saw the guy at Autozone test the old alternator and it come up bad so I know it was no good.

Now I see after using a Duralast non OEM alternator for a few weeks that my belt looks like this (see below):

I had some squealing at cold startup once yesterday but it went away.

I put a reman Denso alternator from Rock Auto (remanufactuted in the USA!) back on.

I’m assuming a bad tensioner which looks like quite a pain in the ass.

What do I do first? I’ve read every thread I can find. Seems I need to test every pulley and the tensioner (how?) with the belt off, right? Do you really have to take the AC compressor off to do the tensioner?

Thanks for any help in advance.

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How many miles on that belt? Squealing happens on the ribbed surface typically, and from your pic that side doesn't seem to have any cracks indicating excessive age. It may be glazed, hard to fully see in the pic.

I'd remove the belt and check all 4 idler pulleys (2 on upper side, 1 on tensioner, 1 on lower side near AC compressor. Two basic tests:

1.) Spin the pulley, should not freewheel excessively (grease gone) or show significant resistance or detectable grinding.

2.) Grab the pulley and check for wobble. Should have no detectable play.

If no findings, I'd get a new belt. For a bit more $, the Toyota Tacoma part is cheaper than the 4Runner one, same length but is made by Bando in the US. Part # I used was 90916-A2001. Monitor the new belt for signs of excessive wear.

I suspect the belt is routed wrong. check the upper idler pulleys. im guessing you have them on the wrong side of one pulley, and have missed the other one entirely...

Thanks guys

Take it to a good mechanic at a shop with a bunch of lifts.

I handed my mechanic a new serpentine belt and he said the old one was fine - and went ahead and installed a new Denso AC Compressor ($190 at Amazon).

mechanic was right, as one year later no problems, squeals and plenty of cold air.

Looks like it is routed right. I just double checked it again.

Will do as you instructed. That's the gist of the threads I've been digging through. The belt has prob 20,000 or maybe 25,000 miles.

I think the new alternator was crooked. I never got a straight edge on it; I just pulled it and put the remaned denso unit in. But it had a lot of play in that bottom bolt. Both Denso alternators were solid feeling, with only one way it could bolt in. The Duralast one seemed cocked when it was tightened. I noticed the rubbing on the back of the belt the first day after I put in the Duralast, and it seems to have gotten worse over the last 2 weeks.

I'm going to do exactly what you suggest. I found a thread about regreasing the bearings of the pulleys if they spin straight. This 4runner has 220,000+, though. I'd say the odds of the pulleys and/or the tensioner being in good shape are pretty low.

You'll likely be amazed at how much quieter the engine is with new idler pulleys. So much cold "engine noise" in mine disappeared completely after I replaced all 4 of the idlers at 178K miles, they were all shot to varying degrees.

I'm excited now. It does have a bunch of squeaky squeaks, that are probably all 4.

Is the tensioner that much of a *****? Did you drop the compressor? Or did you just swap the pulley on the tensioner (seems 50/50 on that one)?

I did mine last Summer while I had the front apart for a timing chain replacement, so the compressor was unbolted anyway. It was a "while I'm in here" and there was no indication that it needed to be replaced at 178K miles.

I would not go through the trouble of removing the compressor and replacing the tensioner unless I was certain that the tensioner spring was worn out. It's tight quarters, and the 4 compressor bolts require precision torquing in a specific sequence per the shop manual.

I'd just replace the pulley(s) and belt, unless a known-good belt slips under load e.g. squealing during AC compressor engagement, power steering at full lock, or cold startup. Your current belt is definitely not known-good based on the pics.

Just an FYI, I have the V8..but my tensioner had plenty of tension but the bearing in the pulley was shot so I just replaced the pulley/bearing, it was not all that bad to get at it, on the V8 you would have to remove the AC compressor as well to replace the entire tensioner assembly, just the pulley I had done inside of 30 minutes and that included fighting to get the old belt off because whoever replaced the belt last installed the wrong belt which was too small making it very difficult to remove because the tensioner was close to being maxed out and could be why my bearing when bad, when I installed the correct belt after replacing the pulley it went on easily.