Engine Noise....????

[Tenn_volsfan56]

I have been noticing for the past few months a noise that sounds like thumping coming from under the hood. The noise only happens when the A/C is on and the car is in gear. In P and Neutral with the A/C on there is no noise. Only when its under a load i guess is what you would call it.

I searched it and only came up with this that even sounded close to my problem. 3.4 Engine Thump/Knock [Archive] - Toyota Nation Forum : Toyota Car and Truck Forums

Any ideas?

Thanks,

 

[Tenn_volsfan56]

Bump

 

[LittleCaesar]

How old is the AC belt? How is the idler pulley? Do you hear the noise under load with the AC off? If no to the last question, the compressor may be going south.

 

[Tenn_volsfan56]

Thanks for the reply. I've owned my runner for about a year and a half. Not sure how old the belt is. Never hear the sound when the a/c is off.

 

[LittleCaesar]

Next time you have the AC on and with the 4runner in park, open up the hood and listen for the sound. Even if is not audible under load while in the car, I will bet more than likely you could hear it otherwise.

Change the belt(s) if they look worn. While the belt is off, spin the idler on the AC bracket and the compressor clutch.

 

[Tenn_volsfan56]

I'll try that. I appreciate it man.

 

[jonwilly2]

Its a little work but take the belt off for the AC. If you still hear it check the timing belt by pulling the upper cover and inspect what you can see. Mark the spot you just looked at with a marker and turn the engine with ether a socket wrench or by using the ignition and only doing a jolt on the starter. If the belt is fine then that just leaves something metal like a bearing. Hopefully its just a old belt with a piece flapping or missing not a main bearing or something.