Is it safe to mix different types of oils?
It is generally safer not to mix different oils. Shell is a responsible oil marketer and therefore oil compatibility testing is an integral part of all design studies ensuring that it is safe to change to Shell products at any time. It is not a disaster if two oils of similar specification are mixed by necessity or accident so long as the oil mixture is drained out as soon as possible and replaced with a new fill of a single oil.
*Sadly, we had to bring back ads too. Hopefully more targeted.