[Huskymaniac]

I need to clarify some confusion on my part. Rotella T6 actually DOES have Molybdenum in it! But that is a recent development. There was a reformulation when they classified it as a CJ-4 oil. While it is still considered a diesel oil, the Mo containing molecule is different from MoS2 and is supposedly safe for diesel engines.

So that Rotella 5W40 oil would seem to be a good candidate for a gas engine that has shearing concerns. HOWEVER, I am actually concerned that it is overkill and maybe too thick for the SVX engine. It is actually thicker than your average 10W40 dino oil.

What might be a better option, for those not looking for the seal conditioners of a high mileage oil, is the Mobil 1 0W40. It is closer to a 10W30 than a 10W40 at operating temperatures. It has an excellent HTHS viscosity so it shouldn't shear even in an STi engine. It also has great low temperature viscosity for those of us in cold climates. And its high temperature viscosity is low enough for those in southern climates. If I lived in a desert AND I beat the snot out of the car, I might lean toward the Rotella T6. One other thing to note is that the Mobil 1 0W40 has a very high TBN value which means it should be great for extended oil change intervals. The Rotella is high too but not quite as high and VOAs (virgin oil analysis) on both oils have shown that the Rotella sometimes comes up lighter while the M1 tends to be higher than the number in the datasheet. It appears as though Shell is optimistic while Mobil is conservative.

I went back and looked into this more due to a conversation with John. I liked what I saw from the M1 0W40 so much I am actually considering using it. If the UOA (used oil analysis) on the M1 5W30 high mileage oil shows insufficient TBN after 6000 miles or too much TAN (acid), I may give the 0W40 a shot. I still want some extra seal conditioners to hold off leaks on our notoriously leaky Subaru engines so I will either blend the M1 0W40 with the M1 5W30 HM or I will add Lubegard Bio/Tech Engine Protectant to the M1 0W40 oil. The Lubegard product adds some seal conditioners and a special polar ester molecule that creates an additional protective coating on engine parts.

Note to John:

That Lubegard product might be a good idea for you. The added ester film on the metal surface will help avoid damage when you start the car after it has sat for a long time. The M1 5W30 ESP oil seems to have nearly perfect HTHS values and you should not need to go to 10W30 in the summer. I'm not sure why the HTHS is so high for a 5W30 but, at high temperatures, it acts almost like a 10W30. The only caveat with this oil is the low TBN values people are reporting through VOAs. This can't be used for extended oil change intervals but I doubt the mileage you rack up between oil changes is even 3000 miles so that is probably not a factor for you.