Engine knocking/ticking on 2002 Jeep Wrangler

67,000 miles just changed my oil, use synthetic and now the engine has a loud tick or knock at cold start up. After it warms up it quiets down to where you can hardly hear it at all. Once warmed up the oil pressure drops to 40 at idle.???

Asked by for the 2002 Jeep Wrangler
Your oil filter has a anti drain back valve. This valve is probably defective allowing oil to drain back to the oil pan, thus basically losing prime. When you start the engine, the top end is "Dry", which would cause the ticking noise. Another possibility is you are hearing "piston Knock". Piston knock is not harmful to the engine. As the engine warms up, the piston expands, thus the clearance between the piston and the cylinder is less. This is a result from normal wear, especially if you have a 2.5 - 4.0l engine. Your oil pressure, 40 psi @ idle is on the high end of normal. Normal oil pressure at idle can be as low as 5psi. At 3000 rpm, normal is considered to be between 25 and 80 psi.
Thanks, I'll try a new one. Just wondering would this still cause it to hav a light tick or knock even after its warmed up.