Oil is oil, so changing brands of oil has no effect upon anything. My 1998 XJ has +264,000 miles and gets whatever brand of oil is in the 55 gallon drum at the oil change place, or is on sale at the nearest auto parts store. Old oil has had its additives used up and could possibly be considered thinner than new oil.
Naturally, you need to identify the source/cause of the noise, and then determine if it a usual/normal noise for a Jeep with the same age and mileage, or if it is a sign of a problem. Consider piston slap, lifter noise, or simple carbon build up as possible causes of the noise.
SUBJECT: Carbon Buildup On Top of Piston
DATE: Dec. 31, 1993
Symptoms vary from light ticking, to a ticking/hammering to a hammering/knocking noise as the carbon buildup increases with mileage and time. The noise is constant and more pronounced when the engine is cold. However, it may disappear when the engine warms up. The noise is most noticeable during idle, but will get louder as engine speed increases.
Carbon buildup is a relatively new condition that occurs during the combustion process and results from certain compounds in gasoline. These compounds form deposits on the top of the piston and cause contact between the cylinder head and the piston. The condition affects all gasoline engines and is industry wide. The brand of fuel and the type of detergents used by the gasoline supplier significantly contribute to the condition. Also, vehicles used in city traffic or light duty cycle operation are more prone to incurring the condition.
Make sure that all vehicle
systems are operating as designed.
Using the Mopar Diagnostic System or the Scan Tool (DRB II) with appropriate diagnostic procedure manual, verify that all engine systems are functioning as designed. If Diagnostic Trouble Codes (DTC s) are present, record them on the repair order for future reference, and repair as necessary.
If all engine systems are functioning as designed, ask the customer about the fuel that is being used in the vehicle. If there is a question about the quality of the fuel, suggest that only fuels which are "warranted" by the gasoline company against the build up of deposits be used.
The use of Mopar Fuel Injector Cleaner has shown reasonable results in removing carbon buildup deposits. Add one bottle of Mopar Fuel Injector Cleaner (P/N 4318007) to a full tank of gas.
CAUTION: UNDER NO CIRCUMSTANCES SHOULD THIS FUEL INJECTOR CLEANER BE ADDED TO A PARTIALLY FILLED FUEL
TANK. ALSO, LIQUID CLEANERS ADDED THROUGH THE ENGINE INTAKE SYSTEM COULD RESULT IN BENT CONNECTING RODS DUE TO HYDROSTATIC LOCK.
Mopar fuel injector cleaner is not intended for continuous use. Owners should be advised of the cause of the noise problem and a recommendation should be made to try other brands of gasoline.