Engine oil

[mints73]

Can you mix oil ie if you need to top up between service and you are not sure make of oil in engine.

Does it do any harm if semi synthetic and fully synthetic are mixed if the grade is similar.

 

[Burnerman]

Adding semi synthetic oil to fully synthetic lowers the specification of the fully synth to the semi...if you get my drift!
Whether this is a big issue depends on the individual engine...but if its meant to use semi synthetic then its fine.
John