* Coolant Leak into Combustion Chamber: This is the most likely culprit. The white smoke will often have a sweet smell (like antifreeze). The cause could be a cracked cylinder head, a blown head gasket (very common on these engines), or a cracked engine block (less common). You'll likely also see low coolant levels and possibly milky oil (coolant mixing with the oil).
* Burning Oil: White smoke can also be caused by burning oil, but this is usually thicker and bluer-tinged white than the smoke from coolant. Causes for oil burning include worn piston rings, valve stem seals, or leaking valve guides. You'd also likely see low oil levels and potentially oil consumption.
* Condensation (Cold Weather): If the Jeep hasn't been driven for a while and it's cold outside, you might see some white smoke initially as the condensation in the exhaust system burns off. This usually clears up quickly.
* Steam from Leaking Exhaust Manifold: While less likely to be consistent white smoke, a leak in the exhaust manifold near the coolant passages could cause steam to escape. This would often be accompanied by other sounds or obvious leaks.
To diagnose the problem:
1. Check coolant levels: If the coolant is low, it strongly suggests a leak into the combustion chamber or an external coolant leak.
2. Check the oil: Inspect the oil dipstick for a milky or foamy appearance. This is a clear sign of coolant mixing with the oil.
3. Look for external leaks: Carefully examine the engine for any visible coolant leaks around the cylinder head, water pump, hoses, etc.
4. Smell the exhaust: A sweet smell indicates coolant. A burning oil smell indicates oil.
5. Pressure test the cooling system: This will help pinpoint leaks in the cooling system.
6. Compression test: This test checks the compression in each cylinder, which can help identify a blown head gasket or other internal engine problems.
In short: While condensation is a possibility, the white smoke combined with a 1999 Jeep suggests a coolant leak into the combustion chamber is the most probable cause. Ignoring this could lead to significant engine damage. You should have a mechanic diagnose the issue promptly.
