2001 Pontiac Grand Prix SE **Motor Knocking Sound**


I have this Grand Prix w/ about 110,000 miles and for the last 20k-30k miles there has been a motor knocking sound that gets quieter as the engine warms up. Recently, all the valve lifters and intake/engine gaskets were replaced and a thicker oil was used in the change. This seemed to further quiet the knocking, but it’s still there. What could be the source for this sound and how much could this repair cost?

One more thing, as a result of emptying and replacing the coolant, I haven’t been able to get the “Low Coolant” light to go off, despite multiple attempts to open the pressure-release valves to get the air bubbles out. Any idea on how to do this as well? (The coolant sensor was replace not too long ago, a couple years back)

Thanks, and I appreciate the help!