Castrol don't even make a proper fully synth - their synths are blends - but they used their muscle and financial might to get the rules changed as to what you can call synthetic. Check out the cold pour stats compared to Mobil 1 - that's the dead give away as to whether you're buying genuine fully-synth or not.

Any oil meeting the spec will do the job - better oil might last longer due to better additive packs but that's about it.

Well I came across this earlier.

Castrol Magnatec 5w/30 Fully Synthetic .SPEC API SL A1/B1 4 litres £28.00

Car Lube 5w/30 Semi Synthetic SPEC API SL A1/B1 5 litres
£14.00.

Which one would you use? If you change your oil and filter at 3000 miles ,
does it really matter whether its Full or Semi Synthetic.

groenendael said:

Well I came across this earlier.

Castrol Magnatec 5w/30 Fully Synthetic .SPEC API SL A1/B1 4 litres £28.00

Car Lube 5w/30 Semi Synthetic SPEC API SL A1/B1 5 litres
£14.00.

Which one would you use? If you change your oil and filter at 3000 miles ,
does it really matter whether its Full or Semi Synthetic.

Click to expand...

Can i have some time to think about that one?

groenendael said:

Well I came across this earlier.

Castrol Magnatec 5w/30 Fully Synthetic .SPEC API SL A1/B1 4 litres £28.00

Car Lube 5w/30 Semi Synthetic SPEC API SL A1/B1 5 litres
£14.00.

Which one would you use? If you change your oil and filter at 3000 miles ,
does it really matter whether its Full or Semi Synthetic.

Click to expand...

Which engine?