When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Ideally you should only mix them if you are topping-up and don't know what oil is already in the sump. Back in the old days the big no-no was mixing of mineral oil with castor based oil (eg Castrol R)
JohnD