'00 3.8 Rattle Along Serpentine Belt

[jgilhuly]

90K miles. Occasional drops on the floor poss below the front seal. No major oil loss. Recently started getting an obvious rattle or knocking sound from somewhere along the serpentine belt. Most obvious at idle when the AC compressor is on but you can hear it on startup and intermittently at idle without AC on. Goes away on acceleration.

Shop is telling me it's internal, possibly the crank. Waiting for more specifics. I trust these guys but if we're talking rebuilding the bottom end this is probably a deal breaker.

Any opinions? Any history on this engine of this type of thing?

Thanks...

[GTP Dad]

Try replacing the tensioner for the belt and check the harmonic balancer. Both will make similar noises. Also it could be the alternator but doubtful. To see if it is the balancer remove the belt and start the car. If no noise replace belt and try again at least you have eliminated the balancer. I truly suspect it is the tensioner pulley although check the water pump too while you are at it. I have serious doubts about the crank issue. Just a way to make more money on the mechanics part!

[jgilhuly]

Thanks, Dad, your opinion concurs with everyone else I've talked to about this **except my mechanic** so the van is on its way to a second opinion. The first guy did claim that he pulled the belt and the sound persisted but I'm still skeptical. The thing that gets me (and everyone else) is, if this is some fundamental internal problem, why does it 100% go away on acceleration and why is it ONLY evident on cranking and when the compressor is on--and even then, only at idle? I can drive all day with the AC off and never hear the noise. I can kick the AC on when the engine's at speed and never hear a thing. Wouldn't almost any internal problem show itself regardless?

Thanks again for your input!

[KManiac]

I just cured a similar problem in my 1998 Town & Country, which I just posted in another thread. The cause of my rattling problem was the belt tensioner, not the pulley on the tensioner, which i replaced separately, but the spring loaded portion of the tensioner. A buddy finally isolated the noise with a stethoscope while I sat behind the wheel with the engine idling, in gear, with the A/C on. I tried to replace it myself, but found that I could not see or reach the tensioner mounting bolt with my own tools. I paid the dealer to replace it for me. Now the rattle is gone.

Good luck with this and let us know what you find and do.

[jgilhuly]

Finally got around to this. Other posts on this noise have pointed to the flex plate and turns out that was the case for me too.

One mechanic offered to replace the tensioner and harmonic balancer just to try it out and the noise persisted so he apparently used the trans inspection window to watch the action of the flex plate as he turned the crank and he said he could see it "hitting the pan". I don't know trans anatomy at all so I hope I'm not mis-stating this. I wonder why the first tranny guy didn't spot this?

Anyway, for what it's worth, the trans shop had seen plenty of Fords with this problem but this was their first Dodge.