2005 Silverado with extremely low mileage on a 4.3L V6 engine seems to have the serpentine belt tensioner moving a lot during idling. It was moving back and forth about an inch at idle. I tried replacing the tensioner, but it is still moving a lot. Seems to be worse as the AC compressor kicks on. If I give it a little gas, everything stabilizes. None of the pulleys appear to be bent or wobbling. This truck only has 4500 miles (yes, that's not a typo). It was a farm truck that just didn't get driven much. In every other respect, this truck runs fine.

The question is: Is this normal for this engine? Is it just the load on the belt and the slow speed of the engine that's causing the motion on the tensioner?

If it's not normal, what should I look for to be the problem?

I'm concerned that with so much motion in the belt tensioner, the serpentine belt could jump off.

 

Could the tensioner spring be weak or broken? How much is it moving?

 

I did replace the tensioner, so I don't think the problem is the tensioner.

I have been wondering if it isn't the belt. Perhaps the belt has hardened with lack of use and is slipping at certain places. The truck hadn't been driven at all in the past 4 months.

 

Anyone have any ideas on this issue? This is an extremely low milage truck that has spent most of the last 2 years parked. Maybe been driven once every 3 months or so. If I had to guess, I'd try a new belt thinking that maybe it had hardened and is slipping a little. The truck is located remotely, so I have to buy any parts before I go there.

 

if the belt vibrates more when you have AC on, I would suspect the AC compressor is faulty. Especially if it hasnt been used much.
I have a 2003 silverado that I originally suspected the tensioner at AC. My air was frosty cold, therefore I did not think anything was wrong with it. I placed a new tensioner and belts on, started vibrating more and literally slung the new tensioner out from under my truck, Had to have AC system replaced (condenssor, dryer, vacuumed and recharged) a friend of mine owns an auto shop and gave me a discount, still costs me near $700.

 

Well, I did have the AC on when I noticed the issue. I sure hope it's not the AC. Replacing the compressor, etc is usually a $1200 job.

It still sounds strange that an otherwise working AC would be the problem. Why would lack of use cause it to suddenly load the belt so much and cause vibration?

I'll definitely check it with the AC off next time I'm on the farm. The truck is stored at a remote location, so I can't really try things unless I'm there. I'll probably also get a new belt, just in case.

 

What the auto shop told me was the the fluid inside the compressor will turn to sludge putting the compressor in more of a bind, among other things, he said my system was full of metal from the compresor's inerds disrupting.
I have never sat in another vehicle that the AC was that cold, in 100* weather, i would sometimes turn the vents away from me.
I am gonna miss that cold air next summer, as the new system is not near as frosty

 

Okay, time to tell what really happened on this truck. The serpentine belt must are hardened from lack of use. I went to get the truck (remote location) and forgot to get a new serpentine belt before I left home, so I had to drive it as is. By the time I got home (200 miles later), the belt tensioner barely moved. Been driving it like this ever since with no problems. I guess hardened or slick spots on the belt were the problem. Driving it more made it go away.