Originally Posted by kschachn
Originally Posted by Mad_Hatter
That test only establishes that they are miscible, something I already mentioned. The tests of ASTM D6922 do not purport to establish any standard for additive compatibly.
Well but it apparently does say this too (found online, I no longer have access to ASTM tests):
Quote
5.1 It is important that engine oils from different manufacturers be homogeneous and miscible with each other, because operators of automotive engines often do not have prior knowledge of the manufacturer of the oil that is currently used in their application, and engine failure can occur if oils are combined that do not stay homogeneous and function properly.
1. Scope
1.1 This test method covers the determination if an automotive engine oil is homogeneous and will remain so, and if it is miscible with certain standard reference oils after being submitted to a prescribed cycle of temperature changes. This test method is very similar to the homogeneity and miscibility test described in FED-STD-791/3470.1.
I understand what you mean but I think in this case it is more than simple miscibility, more than how water and oil are not miscible. All hydrocarbons used to produce motor oils are going to be miscible I would think, to me this refers to engine damage caused by different oils which was what I was trying to convey earlier.
But thanks for the information.
ðŸ‘..fwiw, I've had to top off using a different brand on past vehicles... I've used a half quart of whatever I've had on hand to make up the .5qt in X.5 sump.. never had an engine grenade on me. Was/were there any ill effects of doing this, don't know. Unless the engine exploded, how would I know unless I was tearing down the engine all the time?... what reference engine would I use? So while I am personally convinced it's not advisable to mix oils as a long term practice, it's probably not a practical concern (something to set your hair on fire about) if you're doing it once in a while and on small scale (1qt + 5qts for example). But who knows, I could very well be wrong in that assumption.
This is such an esoteric topic one that admittedly I don't fully grasp like a formulator does but my hunch is it boils down to how the multitude of additive pkgs react to one another not just in a beaker @room temp but at the extreme ends of the temp scale inside the engine. I think that uncertainty (law of unintended consequences) warrants a "not advisable" from the/some lube mfgs. I know I certainly wouldn't want to be on the hook for something I couldn't foresee.
