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Can I mix different brands of oil?

What are the consequences of mixing Castrol xl 20w/50 with synthetic Penrite 20w/50 classic oil?

Asked on 12 February 2018 by Robin Hall

Answered by Keith Moody
While it's not the best idea to mix different brands of engine oil (because of the different additives used), using two different varieties of the same type of engine oil (in this case 20w/50) shouldn't cause any problems. Even mixing mineral and synthetic oil is generally fine - as long as it's not happening regularly. However, if you are in any doubt, then drain the oil, flush the system through and replenish with fresh oil and filter.
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