I have a theory.........

With most vehicles having intelligent learning map ecu's & cycles per trip, short runs then long runs within a short period surely wreaks havoc with fuel trims & duty cycles, not to mention blocked DPF's that have been caused by the former.

Another theory of mine is that i am a firm believer in running a vehicle for at least 50 miles or more to get the CORE temperature of the engine at a more or less constant.

As with animals & human beings we can feel cold on the outside but we always maintain a core temperature. If our core temperature drops we onset hyperthermia.

An engine is not a living thing & opposite, so to get a core temperature it surely needs a considerable long journey to hit & maintain core temperature.

Think of it this way, a engine has hyperthermia most of the time unless you are a rep or truck driver.

Open the bonnet of a vehicle after a trip from London to Birmingham in poring rain! Most of the engine bay you will find not a hint of condensation.