Originally Posted By: dbrowne1
Originally Posted By: Gokhan
Rotellas (both the T6 and T) don't have friction modifiers. I wouldn't used them in my gasoline engine for that reason, even though they are good oils otherwise. But they are a good choice for motorcycle engines, which require the absence of friction modifiers.
Why would friction modifiers (or lack thereof) be an issue in motor oil that's being used in a motor and not in a differential, clutch, etc.?
T6 contains more zinc than most oils marketed for gasoline engines, so it has enough EP additives. It uses Shell's XHVI Group III+ base oil which is excellent. It carries API gasoline ratings.
If you have a gas vehicle that needs or benefits from a 5W40 synthetic oil, it's probably the best value out there. Not necessarily the best oil if cost is no object, but the best bang for the buck.
Friction modifiers (such as moly) increase the fuel economy and horsepower by reducing surface friction. They also reduce wear by increasing the effectiveness of antiwear agents (such as ZDDP). I like having them in the oil I use.
Delo has plenty of friction modifiers; Delvac has a moderate amount, and Rotella has none.
Rotella is a good oil and shows good wear protection, like all Shell oils (Pennzoil, Formula Shell, etc.).
There are a lot of things that affect wear protection. A balanced antiwear and friction-modifier package is one of them. HTHS viscosity is also very important, larger being better. I prefer 15W-40 for that reason because it has a substantially higher HTHS viscosity than 5W-40. Synthetic or conventional base stocks makes no difference as long as you change your oil before it goes bad (synthetic might last longer).
Coming back to friction modifiers, personally I would use an oil containing them for peace of mind. Others might not care. For wet clutch applications (motorcyles, automatic transmissions, etc.) though, you need to choose an oil with the correct surface friction, and you might be stuck with an oil with no friction modifiers (such as Rotella). Rotella is nicely certified for JASO motorcycle category.
Regarding xW-40 weight oil, you can use it virtually in any engine. It will reduce fuel economy with respect to xW-20 and xW-30 on the downside. It has superior wear protection (increased film strength, especially important for bearings) than thinner viscosities. Higher HTHS viscosity simply means higher oil-film strength. 15W-40 works very well in my gasoline engine and is the standard for diesel engines.
For newer engines you probably don't need to sacrifice fuel economy for slightly enhanced wear protection, unless you're doing a lot of high-speed, high-acceleration, and/or high-temperature driving, which could result in a lot of wear with xW-20 or even xW-30 if that is the case for your driving conditions.