 Although most vehicles now have a temperature-controlled electric cooling fan, ""the unassisted air stream can provide sufficient cooling up to 95% of the time"" and so such a fan is not the mechanism for primary control of the internal temperature.Research in the 1920s showed that cylinder wear was aggravated by condensation of fuel when it contacted a cool cylinder wall which removed the oil film.The development of the automatic thermostat in the 1930s solved this problem by ensuring fast engine warm-up.