Why does a 1998 Geo Prizm need quart or two of oil every weeks so even though there are no obvious leaks on the ground?

Possible Causes:

* Worn piston rings: Worn piston rings can allow oil to seep into the combustion chamber, where it is burned. This can cause the engine to consume oil at a rapid rate.

* Bad valve seals: Worn valve seals can allow oil to seep into the combustion chamber, causing the engine to burn oil.

* Oil leaks: Oil leaks can cause the engine to lose oil, even if they are not obvious on the ground. Check for leaks around the oil pan, valve cover gasket, and oil filter.

* Engine wear: As an engine ages, the internal components can wear out, which can lead to increased oil consumption.

* PCV valve: A faulty PCV valve can cause the engine to burn oil. The PCV valve is a small, one-way valve that helps to control the flow of crankcase fumes back into the intake manifold. If the PCV valve is stuck open, it can allow too much oil vapor to be drawn into the intake manifold, which can be burned.

* High oil pressure: High oil pressure can cause the engine to burn oil. This can be caused by a faulty oil pressure regulator or a clogged oil filter.

* Turbocharger or supercharger: If your vehicle has a turbocharger or supercharger, it may consume oil as part of its normal operation. This is because these components use oil to lubricate their bearings.