When an automatic belt tensioner is rattling, which component is rattling?

Question

I have a rattling automatic belt tensioner on my 2002 Infiniti Q45. I've spoken with 2 mechanics, one of them at the Infiniti dealership, who told me a rattling belt tensioner, while annoying, is not indicative of a failing part. They instructed me to replace the tensioner when the belts are replaced.

Well, the time has arrived for belt replacement and I'm finding there are different components for replacing on belt tensioners: the pulley and the assembly. To see such options on this car, see this O'Reilly Auto page.

It would clearly be much less expensive to just replace the pulleys, but I don't want to bother if it won't fix the rattling.

Answer 1

Pulleys do not usually make a rattling noise, when a bearing goes bad it usually makes a constant grinding or whirring noise, the tensioner itself can make more of a rattling or clicking noise. I know the terms for noises can be confusing.

As a general rule the tensioner pulley, the idler pulleys, and the tensioner assembly itself should be replaced every time the belt is replaced, the new belt technology means belts can in some cases outlast the pulleys and tensioner. If replaced with cheap parts you may still have a rattle.

Another cause of the problem could be the belt itself, sometimes belts develop a weak spot where they stretch. This can the tensioner to constantly move in and out to adjust for the stretch. In extreme cases the belt can cause false engine trouble codes for misfires.

In conclusion, the noise is probably the tensioner assembly. But if you replace any of these parts ur supposed to replace all of them (if you enough money in your account) if one part is worn out the others are close behind.

Answer 2

This question is really subjective. Since we are not there and cannot determine what is going on, it is going to be up to you to solve what you need to do.

That being said, I'll give you two scenarios which might help you get to an end point in your decision.

First:

• If you have the belt off and have access to the tensioner (pulley will spin free), grab the pulley and see if there is any deflection. Deflection meaning, does it move in any way other than going around?
• Does it teeter on its axis?
• Can you hear any noise when you rotate it by hand?
• Does it feel like there is any grinding in the bearing (it should be very smooth and spin freely)?

If you are seeing any or all of these problems, the pulley is probably out of sorts, and it will need to be replaced, BUT:

Second:

• With the belt on and engine running, did the tensioner move a lot when the engine was revved? (I would define a lot of movement as rotating more than 5deg ... subjective, though.)
• Has the belt jumped off of track recently?
• Have you been hearing the alternator scream at you right after start-up?
• Does the belt seem like it is "flopping in the wind" as the engine is running (usually seen on a longer run between pulleys)?

If you are seeing any of these issues, I'd suggest you replace the entire assembly.

Something to think about, at least here in the States, is that if you go to O'Reilly's, get just the pulley, replace yours, and it doesn't solve the issue, you should be able to take it back to them for a full refund or exchange for the tensioner, which will have the pulley on it. Ask them at the counter first, but this should hold true at almost any major auto parts chains.