What is semi-synthetic?

[liquidzyklon]

My first oil change is coming up and I have a quick question. I know that Mazda used to use semi-synthetic (http://www.torontomazda3.ca/forum/showthread.php?t=31658&highlight=semi+synthetic) but now has mostly switched to conventional oil.

But what is semi-synthetic? Is it conventional oil with synthetic additive(s) like the Motormaster Formula 1 Motor Oil? (http://www.canadiantire.ca/AST/browse/4/Auto/EngineOil/ConventionalOil/PRD~0288911P/Motomaster%2BFormula%2B1%2BMotor%2BOil%252C%2B4L.j sp) Or is it any group III "synthetic" (i.e. Mobil 1, Castrol (non-German))? Can someone please clarify.

"True" Synthetics are Group IV or V oil that are Royal Purple, Amsoil, Castrol (German), etc.

[JadeButterfly]

this sticky should answer your questions :): http://www.torontomazda3.ca/forum/showthread.php?t=27852

[liquidzyklon]

I've read that sticky, but it doesn't answer my question. I know that Group III oil can be labelled as "synthetic" in Canada/USA whereas Group IV and V should be true synthetics. But what is semi-synthetic?

[JadeButterfly]

opps sorry bout that...

when i was reading up on oil, i remember semi-synthetic as being a blend of the two as u mentioned...at what % I'm not sure.

[Krisekca]

Semi synthetic = up to 30% synthetic base. * it can be 5%
So it could be Group II and III ... blend.

Good oil doesn't have to be expensive !