Slow Oil pressure drop
 

I need help.
I have a 2005 Silverado 5.3 V8 with 134k miles. The problem started over a highway trip last weekend. The oil pressure was normal at the beginning of the drive (approx 40). About 2 hours in I hear the engine knocking and see that the oil pressure is low. It was half of what I started (approx 20). No warning lights, no check engine lights, just knocking. It took me about 15 minutes to find a town. The oil held at 20, knocking the whole way. I turn it off, and let it cool over lunch. I come back and the oil level is normal. I turn it over and pressure is back to normal, no knock. I buy some Lucas and head on my way to a thanksgiving dinner. It is another 4 hours until the pressure lowers and the knock returns. I pull over long enough to get gas. turn it back on. there is no knock and pressure is fine. Any suggestions on what is wrong?
Thank you in advance!

My buddy had a similar thing on an 01 silverado. He thought he had a bad oil pump but he ran some seafoam through it and it miraculously fixed the problem.

Thanks jrsaathoff! I will try it. For the past week I have been without the knocking noise, however, the oil pressure will slowly drop until it is about 25 and stay there. I have no leaks on the ground and the level is still normal. Is this something I need to have a autoshop look at immediately?

Getting it profesionally checked is up to you. I own a 97 and mine runs an oil pressure of about 25 when it is idling and give or take 45 driving. I do not know much about the normal oil pressure of your model of truck but if it seems significantly low i would try the cheap sea foam method first and if that doesnt work I would get it checked out.

My buddies' truck would drive down the road and fairly quickly drop to a near 0 oil pressure but the sea foam somehow fixed it. Hope this helps you a little bit

I have put half a can of seafoam in the oil and the other half in the gas. There has been zero change in the behavior of the oil pressure. It still drops rather quickly and holds about 20. Could the oil pump be going out? I plan to drop the oil pan and change the filter next week. I will keep you updated. In the meantime, are there any retail parts places that carry a pressure gauge for the silverado? or perhaps the spray cans of seafoam? Thanks for all your help.