Engine thump/knock?

[KJDevildog]

Hey all, looking for a little help diagnosing a thump/knock sound coming from my 06 3.7

The sound is a distant, deep thump sound that is mostly heard in the 800-1400 rpm range. Under heavy acceleration, and at cruising speed or higher RPMs I don't notice it at all. It is much louder under very light throttle, at idle, or when the engine is under load and moving slowly forward or backward. I also notice it seems to get much more noticeable when the AC pump is on. It does it both in gear and in neutral.

We bought the Jeep with 78k on it and now she has 111000. The knock has been there since we bought the Jeep as far as I can remember. It has not seemed to get any worse, nor any better.

Also note that I used the jeep to tow around 5000lbs for 980 miles and it did not seem to do anything to change the knock/thump sound.

I've done a little research and the only things things I can find that are supposed sound like a distant thump are main bearings....

 

[KJDevildog]

Nobody huh?

 

[KJDevildog]

Still nobody huh...

That vague of an issue or what?

 

[TwoBobsKJ]

This is one of those issues that is so difficult to work through - one man's "thump" is another man's "dink." :freak3:

Is the sound from the bottom end or up top? I'd think if it was the main bearings and you've heard the noise for 32,000 miles that one of them would have let go by now.

Have you changed oil brands or viscosity to see if it changes or goes away? Tried synthetic vs standard oil? May be worth a try...

Bob

 

[KJDevildog]

I understand the difficulty diagnosing a sound over the internet. I am pretty sure it is coming from the bottom end near the back. I can actually feel it in the gas pedal, like a pulse with each thump sound.

Edit: Oh, and I run the same Castrol syntec 5w-30 all the time since I bought it. There was one time I ran Mobil 1 but switched right back to Castrol.