Well I am stumped. Something on the front of our 2004 V6 4.0 is squealing so badly it is waking the dead. I had the hardest time tracking down the source. I thought I tracked it to the upper driver’s side idler pulley. I changed the upper driver’s side idler pulley with oem. Still squealing. I removed the upper passenger and lower pulleys. Both seemed fine. Tensioner pulley seems fine. All spin smoothly. Alternator is solid. Power steering has a little in and out play but spinning it is tight.

I intend to replace the upper passenger side pulley with oem I want to change the lower with oem but can’t find a part number. Also what is the tensioner pulley oem part number. Are there any alternatives to oem for the tensioner pulley?

Any secrets for tracking down the source of the squeal? Thanks. Stumped in San Diego. Phil

Go to your autopart store ($10) or even better yet go to Harbor Freight (less than $5) and buy yourself an inexpensive mechanic's stheocope, it will be money well spent, it will come in handy for finding all those squeaks, squeals, knocking and tapping noises that are hard to pinpoint, just be very careful with the probe end around moving parts, belts, fans and etc. but if you're careful you will find the squeal.

Everyone that works on and or troubleshoots their vehicles needs to have one in their toolbox, you will wonder why you have never bought one before.

Mechanic's Stethoscope

Spray your belt with water,if the noise goes away it's your belt,if not it's a idler or your a/c, Alt,water pump or power steering is going out.

The Gates 36174 is a replacement for the lower. There is no replacement for the tensioner pulley but I used the same Gates 36174 and it worked ok. The alternative is to replace the bearing or the whole tensioner assembly. See here for details:

Tensioner pulley on V6, does 36174 work?

https://www.amazon.com/Gates-36174-I.../dp/B001FHQZDI

Finding high pitches squeaks/squeals can be difficult even with a mechanics stethoscope, but if your careful and methodical it can help a lot to rule things out and track down noises. They are certainly a must have tool in my opinion.

Before you do anything else you need to test and check the serpentine belt in every which-way. The belt is what will tell you where to look for the problem. Here is a good read.

Well after changing out both top idler pulleys and the bottom idler pulley with oem, picked them up on eBay for about $27 each. still screaming. A run to O’reilly’s for the gates tensioner pulley. Still screaming. Finally installed the new oem belt, current belt has 15,000 miles on it. Well that was it. The v6 is purring once again. I will hang on to the pulleys that I removed and keep them as spares. Toyota does not sell the tensioner pulley. They only sell the full assembly. I picked up a gates 36174 at O’reilly’s for $70. Probably could have saved $30 had I ordered it online.

Use your oem bolt and washer. Remember the tensioner pulley bolt is reverse thread.

I did pick up a stethoscope at harbor freight $3.99. Much safer than using a long screwdriver.

The various threads on the forum on pulley swaps were really helpful.

All the best.

Phil