White stuff on oil cap?

[Red Herring]

Every time you start the engine it will produce a certain amount of water vapour and some of this will find it's way into the oil. If you only do short trips the oil will never get hot enough to get rid of this water and eventually it won't be able to absorb any more and this will lead to lubrication issues. If I had to do lots of short trips at this time of year I would do two things. Firstly I'd put a strip of gaffa tape across the front of the oil cooler to give the oil a better chance of getting up to temperature, secondly I'd change the oil more often to avoid the water contamination issues.

Here's a link to let you know what the issues are with water in your oil.
http://www.machinerylubrication.com/...ter-motor-oils