[Piotrsko]

One of the reasons for a periodic oil change is that the sulphur in the oil along with other compounds produce acids when there is moisture in the oil, a Combustion byproduct. Not good juju for bearing and structure life in an engine. That said I know of many 20 year old engines that have had 5 year oil changes without much problems, but those are low use trucks.

Heat breaks down oil, most time otherwise it gets thicker.