I've come to the conclusion that the new GF-4 spec is tough to meet, so some of the new GF-4 rated oils are blended with synthetic, am I correct on this? I emailed Castrol a while ago, asking them if their oils will be blended with synthetic. They gave me a cookie-cutter response:
"Please see attached the Typical Inspection Data Sheet for Castrol GTX
motor oil. Castrol does not publish any formulations or changes in
formulations. Our additive systems and base oils are proprietary and
chosen for performance and suitability first. Castrol uses only the
highest quality materials, including base oils."
The data sheet they sent me is out of date, it's dated June 2002. No help there. Someone must know the real deal on this.
"Please see attached the Typical Inspection Data Sheet for Castrol GTX
motor oil. Castrol does not publish any formulations or changes in
formulations. Our additive systems and base oils are proprietary and
chosen for performance and suitability first. Castrol uses only the
highest quality materials, including base oils."
The data sheet they sent me is out of date, it's dated June 2002. No help there. Someone must know the real deal on this.