Originally Posted by Kruse
Originally Posted by RDY4WAR
I never recommend blending different oils. The viscosity isn't the issue.
The problem is base oil incompatibility and additive clash risks.
I'm not saying I'm a fan of mixing oil brands, but can you give us just one link where two oils clashed and bad things happened?
Because I always throw a box of cake mix Y w/eggs from one brand into a bowl with cake mix B w/eggs from another brand and always get a perfectly fluffy franken cake..so why shouldn't it work similiarly in my $10k engine!...‚...‚
Ok, all joking aside...
As a one off situation (like topping off) you'll likely not suffer any adverse effects of any noticeable consequence, when mixing different formulas from different mfgs. However, it must be stressed that the performance of the new brew can not be guaranteed - as I stated already. Additionally, chronic mixing can result in undesired effects, possibly even catastrophic. It's not so much the base oils that are the concern here since oil is oil, miscible
for the most part*. But rather it's the additives.. for example additives in lube A might upset the acid/base balance of lube B for a unknown combined property. As mentioned, antiwear and detergents and corrosion inhibitors in a finished lube are carefully balanced so one doesn't crowd out the other when it comes to competing for surface space within the engine to do their job. Also incompatibilities in additives can result in the formation of solids which can lead to deposit formations. You can also get compatibility issues with seal swellers.
And no.. you're not likely to find a credible account of a mechanic walking out of a shop saying, "Oh my God.. mixing oils grenaded the engine".. not because it can't/doesn't happen but because a) how would the mechanic know the vehicle owner liked to play blender in his/her spare time and b) unless you've been tearing the engine down and measuring and weighing parts regularly, how can one attribute failure to the lube and not say low quality parts or a poor maintenance routine? It's (undesirable effects of mixing lubes) one of those things that any additive mfg and blender will tell you that it
can be a problem (from a (in)compatibility standpoint) but in reality you'd likely never "see" the consequences of such actions.
From a practical standpoint... doing it once here and there (like topping off) is nothing to set your hair on fire about but as a long term practice it's not advisable. Check out the following article to learn more about some of the pitfalls and negatives of oil mixing.
mixing oils