* Valve stem seals: These seals prevent oil from seeping past the valve stems into the combustion chamber. Worn-out seals allow oil to leak down overnight and burn off during startup, creating blue-ish/grey smoke. This is a very common cause of startup smoke.
* Worn piston rings: If the piston rings are worn or damaged, they don't seal properly, allowing oil to leak into the combustion chamber. This also results in blueish/grey smoke, and often more consistent smoking than just on startup.
* Leaking valve guides: Similar to valve stem seals, worn valve guides allow oil to pass down into the combustion chamber. This also contributes to blueish/grey smoke.
* PCV valve: A clogged Positive Crankcase Ventilation (PCV) valve can cause excessive crankcase pressure, forcing oil past seals and into the combustion chamber. This can lead to a range of issues, including smoke, but the smoke might not be exclusively on startup.
* Oil in the air intake: Though less common as a *sole* cause of startup smoke, oil getting into the intake system (perhaps from a faulty PCV or crankcase breather) will burn on startup. This might produce more of a whitish/grey smoke.
Distinguishing the cause:
* Color of the smoke: Blueish-grey strongly suggests oil burning. White smoke usually indicates coolant burning, while black smoke indicates a rich fuel mixture.
* Duration of the smoke: Does it clear up quickly after a few seconds, or does it persist? Valve stem seals often cause brief startup smoke. Worn rings are usually more persistent.
* Oil consumption: Are you noticing significantly higher oil consumption than normal?
* Engine compression test: This helps determine the health of piston rings and valves.
In short: For a 1993 vehicle, worn valve stem seals are a highly probable cause of startup smoke. However, a proper diagnosis requires inspecting the vehicle and potentially performing some tests. You should investigate the PCV valve as it is cheap and easy to replace. If the issue persists, a mechanic should perform a compression test and further inspection to pinpoint the exact problem.
