I read a post recently about Castrol magnatec 5w-30 C3 oil, asking if it was suitable for the Mk3 engine.
I emailed Castrol tech dept and received a reply stating that the C3 is fine to use, its just has slightly more viscosity when hot, giving slightly less fuel efficiency.
A1 and edge are the recommended oils
Yes but remember that Castrol oil only come in 1 or 4L cans and you need 5L FOR THE MK3.
I used the Mobil oil, the only recommended one to use is Mobil Super 3000 5W30 Fully Synthetic Engine oil, 5 Ltrs
While the Magnatec A1 was reformulated two years ago to up the spec to A1/A5 so both fuel saving but better wear protection and shear stability of the oil film.
Some of the cheaper A1 blends do not meet the A5 spec requested by Mazda.
As you say the C3 does meet the spec.
would not magnatec as it is not a proper fully synth. Currently mobil as per above in mine probably millers or something nicer next time.