Recently, my car started to smell whenever I turned on the heater fan. I suspected something broke in the cold weather.

Tonight, I stopped off for gas on my way home and asked the attendant to check the oil (even though they checked it last time I filled up).  It turns out the oil filler cap wasn’t on.  It was just sitting on top of the engine, beside the top of the last oil container I bought.  On the upside, no repairs will be necessary.  On the downside, my pristine engine is now all oily.  (I am surprised I didn’t lose the cap.)