Originally Posted by TheLawnRanger
If temperature plays a part in the fallout and that oil was used in a car, would the additives just mix back into the oil through circulation and rising temperature when in use?
No. Not necessarily. If (and it's a very big if!) that black gunk has dropped out of fresh engine oil, my money is on it being Moly for two reasons.
First, all of the oil soluble Moly additives (ie NOT molybdenum disulphide) I've played around with are deeply, densely black in colour. They're the only additives like this. VIIs & PPDs are colourless. ZDDPs are a nice clear straw colour. Metallic detergents tend to be oak-brown. Ashless dispersants tend to be reddy-brown. The mish mash of common AOs tend to range from clear yellow to pink.
Second, oil soluble Molys aren't necessarily that soluble. Try and blend just 0.5% of Moly into 99.5% base oil and you can whack it up to whatever temperature you like, and stir for as long as you like and it will point blank refuse to go into solution! The trick to getting Moly in solution is to always blend it in the presence of ashless dispersant. It then goes in a treat!
However what you can definitely do in the lab doesn't always translate to what happens at a commercial blend plant & you do have to be very careful. Certain additives have what you might call a 'creeping appetite' for solvency. You blend the oil and it looks great. However these additives, slowly, over time, 'claim' more of the solvency reserve of the oil. In this situation, the least soluble additive component, gradually gets 'pushed out'. If that component happens to be Moly, then you have a problem...