Ondoy,

AFAIK it is not advisable to mix oils of different types and makes as this would degrade it's properties not a cummulative type. Oils are specifically blended to meet their desired requirements. Mixing a syntheric with another mineral oil disrupts this perfect balance which leads the the negative side of the scale. Just choose a good, cheap synthetic oil in the market. As this I would recommend either the Petron Rev-X All Terrain or the Caltex Delo Sports or the Top 1 Synthetic diesel oils which are a cheaper alternative then your chosen Delvac 1. Goodluck.