After a recent oil change the plastic oil filter.

After a recent oil change the plastic oil filter cap kept "popping off" and spitting out all the oil. Having changed the oil filter (that was slightly too big) for a genuine VW type I seemed to have cured the problem. Cap and housing all in good condition too.
However on a few occasions when I first start the van the coolant light comes on and beeps. At this point oil will ooze from the around the plastic oil filter cap. Coolant is at the right level and can not be too hot as the engine only runs for a few seconds before this happens. Seems to happen in cold weather? If I switch off engine and restart a few times it seems to cure the problem? For a week or two anyway! No creamy stuff in the oil or around filler cap and coolant level fine!
Any Ideas what it might be?