Last Saturday, for the first time in year or two, I listened to Car Talk on NPR. One of the callers, a female, was having trouble with her Nissan Sentra. After every oil change, smoke would pour out of the HVAC vents for the next 20-30 minutes of driving.
At first, the speculation was that the mechanics were overfilling the oil, letting some flow over on to the adjacent exhaust manifold, where it would be burned/vaporized and produce the smoke seen by the caller. This had happened with several different garages, though, and it was unlikely that all those different mechanics were making the same mistake.
To make a long story short[er], it was finally discovered* that this woman had been driving around /without an oil fill cap/. Each oil change left her full of engine oil (duh), which would keep sloshing out of the fill tube during acceleration until the oil level was low enough that it couldn't escape. /That/ was the reason it was burning up on her exhaust manifold and sending billows of nasty smoke into the cabin.
I normally hate when people write in all caps, but ... WHY, IN GOD'S NAME, WOULD YOU THINK IT'S OKAY TO DRIVE AROUND WITHOUT AN OIL FILL CAP?! Girls, especially, seem to have a mental/logical disconnect when it comes to automobiles. Everything seemingly works by magic; they're totally clueless about the actual mechanics of operation.
I'm not suggesting that you should have to design a mathematical model of an in-cylinder combustion flame front in order to get a driver's license, but you should understand that basics of how your car works. You should understand how your car gets traction (during acceleration, deceleration, and turning), the purpose of each of the main fluids in your car (engine oil, coolant, transmission fluid, etc.), how varying temperatures affect your car (especially snow & ice), and other such commonsense things. Contrary to popular practice in this country, not every 16-year-old dipshit with a rustbucket, $15, and a lukewarm IQ should be allowed to drive!
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* Note that by 'discovered', I mean 'discovered on-air'. The lady was fully aware that she had been driving with no oil cap, but apparently didn't think it was important or relevant enough to mention.