ScoobyNet.com - Subaru Enthusiast Forum - Castrol Magnetic (semi Synthetic Oil) bad or good?

You probably mean Magnatec.

And its just a brand name..whats in the bottle (full synthetic or part synthetic) varies depending on the viscosity and manuufacturer approvals (i.e BMW LL04, VW 507.00, Merc 229.51 etc ).

For example:

Magnatec 5w-40 C3 is fully synthetic and has EXACTLY the same properties as Edge 5w-40 C3 (read the technical data sheets if you don't believe me). This is a good oil

Magnatec 10w-40 is part synthetic, I suspect will soon be obsolete and it'll probably be re-branded as GTX. This is an old out-of-date oil. (The current retail version of GTX 10w-40 has very similar properties on the data sheets, but has less manufacturer approvals).

For what its worth, have a look at the back of the bottle (or website) and look for oils that have official VW 507.00 or BMW longlife04 (LL04) approvals, these approvals are a sign that they are very good oils. And to me mean a hell of alot more than the viscosity or "how synthetic" it is. And that is regardless of putting it in a Subaru or otherwise.

Beware of cheaper oils that aren't approved but say words along the lines "meets, or conforms to VW 507.00" which mean its NOT been tested or approved by the vehicle manufacturer (Euro car part's Triple QX is a good example of misleading in this way). The reason I mention manufacturer approvals is because the likes of Merc, VW and BMW all have extended change intervals of up to 2 years and therefore demand a much higher quality oil that doesn't degrade as much; I'm not saying this means you don't have to change it as often it just means its far better quality, so can withstand hard use better.

Magnatec 5w40 C3 and Edge 5w-40 C3 have these offical approvals....Magnatec 10w-40 has barely any, and the approvals it does have is for obsolete standards for engines from over 20 years ago, (i.e VW 505.00 which is for 1980's VWs with no longlife intervals )