* Burning oil: This is a serious issue. The smoke will likely smell acrid and slightly sweet. The source could be a leak in the engine itself (e.g., worn valve stem seals, cracked piston rings, a blown head gasket - although a blown head gasket *can* also cause overheating), or a leak in an oil line or the oil filter. Check your oil level immediately – significantly low oil is a strong indicator.
* Burning coolant (but not overheating): While overheating usually accompanies coolant leaks, a small, slow leak might not cause the temperature gauge to climb. The coolant itself is not usually "white-gray" though, more like a whitish vapor or steam. If it's mixed with oil, then it could appear as a grayish white smoke. A leak in a hose or the radiator could cause this. Check for visible coolant leaks around the engine and radiator.
* Steam from a minor leak: A small amount of water or coolant leaking onto a hot engine component might produce visible steam, especially after the engine has been running for a while. This is less likely to be "gray" though and more just a white vapor.
Crucially, DO NOT ignore this. Continue driving with a smoking engine could lead to serious and costly damage. Pull over safely as soon as possible, turn off the engine, and let it cool down before attempting to investigate. If you're not comfortable inspecting it yourself, call a roadside assistance service or tow it to a mechanic.
To help a mechanic diagnose the problem more quickly, note:
* Color and odor of the smoke: Is it truly white-gray, or closer to pure white? Does it smell sweet (like burning sugar) or acrid (like burning oil)?
* Where is the smoke coming from? Try to pinpoint the general area under the hood.
* How long has this been happening?
* Recent maintenance: Have you had any work done on your car recently?
Ignoring this could lead to significant engine damage. Get it checked out promptly.
