Chrysler Repair: 2004 Dodge Intrepid 2.7 DOHC V6 Engine Knock

Question
We own a 2004 Dodge Intrepid with the 2.7 V6 DOHC and have for several years.  The car has approximately 180,000  miles on it and runs like a champ...or did until recently.  We have recently heard what can only be described as a "knock" and "tick" on the passenger side of the engine; however these sounds are NOT constant.  The "knock" began about three weeks ago and was noticeable when the AC was on.  Upon turning the AC off, the knock was no longer there.  The air compressor was replaced, and the "knock" was then present when the car was at idle.  The knock seems to get worse when the engine is under a load (i.e. when the AC is on).  The oil has been changed regularly since we have owned it (about 4 years) and has never shown any signs of shavings or sludge.  The engine has not lost any power, reaction time does not appear to have changed, and there is no other noticeable issue with the engine.  We have been told that the knock is the harmonic balancer, a rod, or possibly a pulley. I am curious if there are issues with the harmonic balancer on this engine or perhaps if you have other suggestions.  Thank you for your time and assistance.  Any information you can provide would be greatly appreciated!!  Chris

Answer
Hi Chris,
Two things to do:
First, I would attempt to localize the sound by listening using an "ear horn", a rubber hose inserted near/in your ear opening (and with the other ear plugged) then move the tip of the hose to various areas of the engine to find the source as close as possible.
Second, is the noise only present when the engine is idling and under load from the A.C,, or is it still present when you increase the rpm above idle, or is it even present when driving it with the rpm over 1500 rpm? When you don't use the A.C. the engine may idle faster a bit and when you mentioned that the noise was absent when you didn't use the A.C. it brought to mind the possibility the oil pressure (which increases with rpm) may be too low at sub-idle speeds and that then can cause an hydraulic valve lifter to 'soften' and thus produce a clicking sound. Were that still the behavior I would be inclined to increase the 'weight' of the engine oil by one step from what you are currently using which will raise the pressure proportionally at all rpm's and thus increase the pressure at idle as well. That could eliminate a lifter clicking sound were that the case.
I have not heard of an issue common to the 2.7L as you describe. But in that time frame there was a tendency for the engines of that era to get gummy as regards the oil passageways. So perhaps you might want to put some internal engine cleaner in the present oil just before you change it (following the directions on the product) then change the oil out to the next higher weight.
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Thanks,
Roland