AWOL:
My car has both front and rear ultrasonic sensors.
I would have thought that they'd be at least IP65 to withstand rain hitting them at over 160 kph.
Fair enough, here is the topic about "preserving" ultrasonic sensors (so it is possible).
http://forums.parallax.com/showthread.php?94365-Using-the-Parallax-Ultrasonic-Sensor-to-measure-liquids-(Need-to-add-protectio