* Worn Piston Rings: This is a common culprit in older cars that consume oil. Piston rings seal the combustion chamber, and if worn, allow oil to seep past into the cylinders and burn, creating blue smoke. This often requires an engine rebuild.
* Worn Valve Guides or Seals: Even after a valve job, if the valve guides are worn, oil can leak past the valve stem seals into the combustion chamber. This can contribute to oil consumption and smoking. This might require further valve train work.
* Breather System Issues: A clogged PCV (Positive Crankcase Ventilation) valve or other parts of the breather system can cause excessive crankcase pressure, forcing oil past seals.
* Leaking Oil Seals: Various seals throughout the engine (crankshaft, camshaft, etc.) can wear out and leak oil. This oil may not necessarily be burning, but it can contribute to oil consumption.
* Cylinder Head Cracks (Less Likely): Although less probable after a valve job, hairline cracks in the cylinder head could allow coolant and/or oil to mix. This would likely manifest in other symptoms as well (like milky oil).
* Improper Valve Adjustment: Even after a valve job, the valves might not be adjusted correctly. Incorrect adjustment can lead to burning oil or other performance issues.
What to Do Next:
1. Compression Test: A compression test will reveal the condition of the piston rings and cylinders. Low compression in one or more cylinders points towards worn rings or other internal damage.
2. Leak-Down Test: A leak-down test is more precise and can pinpoint exactly where compression is escaping (piston rings, valves, head gasket, etc.).
3. Inspect for External Leaks: Carefully check the engine for visible oil leaks around seals and gaskets.
4. Check the PCV System: Inspect the PCV valve and associated hoses for clogs or damage.
It's important to have a qualified mechanic diagnose the problem. The cost of further repairs on an older car like a Geo Metro needs to be weighed against its value. The tests mentioned above will help determine the extent of the problem and if repair is worthwhile.
