A friend of mine shared this post with me. I cannot agree with the author on reason(s) #1/#3 because many HDEO's are dual-rated. For Reason #4, it can be difficult to distinguish the differences between fuel dilution related shearing and actual viscosity breakdown. I am not sure on #2, but I would assume that any dual-rated HDEO would have addressed this issue. Thoughts?
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Link to the full post (I omitted some parts in my quote): https:/
Reason 1: Primary ZDDP. What most people just call Zinc, ZDDP is an additive package in oil that is known for anti-wear properties. I'll spare you the science behind ZDDP decomposition tiers and the nature of boundary lubrication, but what you have to realize is that there are 200+ formulations of ZDDP and they are not all equal. They come in two main categories: primary and secondary. Primary ZDDP is used mostly as an antioxidant to fight oxidative thickening in engine oils in high-heat applications, of which there are plenty in diesel engines, and is also geared more for lower friction coefficient. By contrast, gasoline engines either use mostly secondary ZDDP with some primary, or exclusively secondary (which is the case of higher quality oils), and is geared more for tribofilm formulation. Basically, your 1200ppm of Zinc in Rotella T6 is not actually protecting better than 800ppm of Zinc API SN spec synthetic oil and certainly not better than a high secondary ZDDP formulated gasoline engine oil. Reason 2: Anti-foaming. Also referred to as air release, the oil has to release air pockets generated during friction and movement. Rotella is not very good at this, and that's OK when you are running a Detroit Diesel with a 2100RPM redline or even a 6.7 Powestroke with a 3400RPM redline (where the anti-foaming starts to become a bigger issue), not so much when you're running a Subaru FA20 with a 7400RPM redline. Under extended use, this can eventually aerate the fluid enough to cause catastrophic failure, or at minimum power loss. Reason 3: Detergents/Dispersants. Diesel engines typically deal more with soot handling and dispersion, so the additive package is designed accordingly. On the other hand, gasoline engine detergent packs are designed more to handle acidity. This discrepancy can also result in reduced performance in gasoline engines as the detergent tries to clean the cylinder walls, which compromises the seal between rings and cylinder walls and reduces compression and efficiency. Reason 4: The other day someone challenged me to post oil analysis reports of Rotella T6 shearing (thinning) in viscosity. I did a google image search for Rotella T6 (virgin viscosity of 14.9 cSt) and struggled to find a single oil analysis that was actually in-spect! In fact, I'd say 9/10 oil analysis reports showed that it had sheared in viscosity. If you're looking for a high quality base oil with additives that don't shear in viscosity, this isn't your best option. Now I'm sure I'll get the classic "I've been using this oil and nothing has blown up yet" rhetoric by people who are too cheap to consider better options like AMSOIL, Driven Racing, Motul, and Schaeffer, but that doesn't mean that the product doesn't have its deficiencies simply because you want it to work. I realize people have a higher tendency to believe information that they agree with regarding a cheaper product than a more expensive one, but unless you already knew everything I presented in this post, you ought to reconsider your lubricant choice in gasoline engines (especially high-revving and turbo gasoline engines). There are far better options on the market that will protect better and make more power. Feel free to share wherever appropriate.