* Valve stem seals: These seals prevent oil from leaking past the valve stems into the combustion chamber. When they harden and crack (common with age), they leak more readily when the engine is idling at low pressure. The oil then burns in the cylinders, creating blue smoke. This is a very common cause of oil burning, especially at idle.
* Piston rings: While piston ring wear contributes to oil burning overall, it usually manifests more under higher engine loads. However, severely worn piston rings *could* contribute to oil burning even at idle, especially if there's significant blow-by. This would likely be accompanied by other symptoms, such as low compression and excessive blue smoke even under acceleration.
* PCV valve and system: The Positive Crankcase Ventilation (PCV) system is responsible for venting crankcase pressure. A faulty PCV valve or clogged lines can cause excessive crankcase pressure, forcing oil past seals. This is less likely to be the *sole* cause of significant oil burning at idle, but it can exacerbate the problem if other issues are present.
* Oil leaks: While not directly *burning* oil, significant leaks into areas where the oil can drip onto hot exhaust components can create the smell and appearance of oil burning. Check for leaks around the valve covers, oil pan gasket, and rear main seal. These leaks would show oil spots or trails in the engine bay.
* Worn engine: While less likely to be the primary reason for *only* idle oil burning, significant wear in the engine itself (cylinders, pistons, etc.) could worsen the problem.
Troubleshooting Steps:
1. Check for oil leaks: Visually inspect the engine for any obvious oil leaks. Pay close attention to the areas mentioned above.
2. Check the PCV system: Inspect the PCV valve for proper operation. Remove and clean or replace it if necessary. Check the hoses connected to the PCV system for clogs.
3. Check your oil level: Regularly monitor your oil level. Excessive oil consumption is a clear indicator of a problem.
4. Observe the smoke: Note the color of the smoke. Blue smoke strongly suggests burning oil. White smoke might indicate coolant leaks.
5. Compression test: A compression test can help assess the health of your piston rings and cylinders. Low compression in one or more cylinders points towards a more serious engine issue.
6. Leak-down test: This test can pinpoint the source of compression leaks (past rings, valves, etc.), which can be very helpful in diagnosing oil consumption problems.
Important Note: A 1991 Lincoln Town Car is an older vehicle. The issue might require a professional mechanic to diagnose and repair accurately, especially if it involves more complex engine work like replacing valve stem seals or piston rings. These repairs can be labor-intensive.
Before undertaking any repairs yourself, accurately identify the source of the oil burning. Trying to fix the wrong problem can be expensive and may not solve the issue.
