2006 5.3L - Oil Pressure Drop

[GMCanuck]

So we're in the middle of a long road trip in Alaska and the other day I notice my oil pressure was dropped at idle - don't believe it has ever done this before. Stayed at around 40psi or slightly higher at highway speed, then dropped to just under 30 at idle. Checked the oil and noticed it was down a liter (we've put on some miles but I failed to keep checking it). Topped it up hoping it would return to a consistent 40psi but am still getting the drop.

 

I am hearing some lifter clacking (if that's what it is) but I've had this for a while. Engine just rolled over 160,000 km (100,000 miles).

 

So is it possible I damaged something by letting the oil run a little low, or am I fretting over nothing? We've got a few more long days before we're home and thought I'd reach out for some peace of mind.

 

Thoughts?