I like many others am a huge fan of Rotella T6 5w40. I run it in everything I own, its great stuff. Some of you may know but Im sure others dont, they are now making our favorite oil in 15w40 flavor. For the warmer weather coming up I think running a slightly thicker oil would be a good idea. I like to drive in a spirited fashon and with 296whp a 15w40 oil would be ideal I think. I just changed the oil today from T6 5w40 to the new 15w40. Not much to report yet but I am getting 5-10psi of extra oil pressure at all rpms which makes me feel warm and fuzzy. I think for the guys that track their cars the thicker oil should prevent shear a lot better as well. Ok, PSA over everyone return to their regularly scheduled programming.

 

Interesting, though isn't the viscosity of the oil going to be similar once up to operating temp when discussing 15w40 vs 5w40?

I don't know much about oil. Educate me.

 

Yes, the warm viscosity will be similar between the two but the 15w40 will be more stable as oil temps rise. lower viscosity oils have a tendency to shear at high temps which is bad because that means the bearings are dry right when you need them to be lubricated the most. The difference between 5w and 15w is mostly the cold flow, if temps are above 45-50* there isnt much of a difference between the two when cold. I think the thicker oil also might burn off slower for cars like ours where we have built motors with loose ring gaps.

 

Would be interested to see a Blackstone report on the 2 oils. I know the new 5w40 isn't the same as it used to be.

 

There is a thread on bitog for both. The new formulation still has a pretty good add pack. Less magnesium but lots more boron.

 

Used this in my last oil change. The additive package of the 15w-40 is the same as the regular 5w-40 T6, it just utilizes a thicker base oil. Here is the BITOG thread with the VOA of the new 15w-40 T6 along with a comparison to the CJ-4 and CK-4 (old and new) 5w-40 T6 formulas. The thicker base should be good for shear resistance. Enjoy!

 

Thanks for the tip, I am due for an oil change.