GTX vs Syntec


Staff member
Oakville, Ontario
In looking over the technical specs for Castrol's oils, I noticed something that doesn't make sense to me and I was hoping someone could explain it. In 5w30 viscosity only, the lower cost GTX has a better HTHS than the more expensive Syntec! GTX's HTHS is 3.1 while Syntec is 2.92. I was under the assumption that the base oil is one of the main things that determines the HTHS value, so if Syntec uses a group 3 base oil while GTX uses a group 2, how can GTX show a better value? Could it be the fact that GTX has a viscosity of 10.7cst at 100c while Syntec is 9.7cst at 100c? It still seems strange to me that their top level oil has a poorer showing on this test than their lowest cost oil. FWIW, their High Mileage 5w30 shows an even better HTHS of 3.3. It has a viscosity of 11.9cst at 100c, so it's almost a 5w40. I'm still planning to test out GTX vs Syntec in my sister's 99 Civic. The new plan is to run two 6k intervals of each oil (for a better test than my previous plan of only running one interval of each) to see how they compare. I'm betting GTX shows equal or better wear numbers than Syntec does, at a fraction of the price (up here GTX is $5.98CDN in 4L jugs vs Syntec at about $25-28CDN)
Louisville, KY
Yes it the higher viscosity. Higher viscosity = better HTHS. So the qluaity of the base oil isn't decisive here always. having said that, I still would have expected a group III to do better, but oil analysis from many sources, indicates that GTX is an all 'round better oil than the Syntec. Fred.... [Smile]