Castrol
This page deals with Castrol brand oils
Introduction
GTX Ultraclean seems to be not only the best Castrol oil, but one of the best low-cost oils we have tested. High Mileage performs rather average.
Legend
N/A = NO ADDITIVES
M# = SQUID INK ADDITIVE MIX VARIATION
C# = CUSTOM MIX, SEE UNDER CHARTS FOR MORE DETAILS
Results
GTX High Mileage 10W30
Recommended blend: M7
Rather mundane 30-60 minute performance, becomes bad at 120 minutes. In a city car that does not get put under heavy load for long periods of time this may be fine, but with SQUID INK M5 or M7 blends this becomes a quite excellent oil with relatively low temps and required power. Would not recommend without SQUID INK M5 or M7. The M7 blend reduced the scar size by nearly 50%, and decreased power usage by over 15% (peak).
GTX Ultraclean 5W30
Recommended blend: M7
At $22-$25 per 5 quarts this is one of the best low-cost oils tested. Really solid base performance in the 60 minute stress test, that becomes outstanding to the full 120 minute stress test with the use of M6 or M7 SQUID INK blends. M7 reduced the wear scar size by nearly 50%, and reduced the cylinder weight loss by almost 90%!
