Originally Posted by JCL

Agree with all the above posters on the general theme here, but I don't agree that this is caused by the oil separator. We are confusing cause and effect here.

Milky oil is caused by water/coolant in the oil. If the oil is milky when you check the dipstick you are looking for a coolant leak, ie headgasket or something similar. If the oil is dark, but the milky paste is under the oil filler cap, then it is still caused by moisture, but it is likely caused by condensation (small amount of moisture, and localized). The root cause of this is short trips that don't allow the engine to fully warm up. The engine goes through multiple cooling/warming cycles in this case, and each time the condensation forms, mixes with the oil, and causes this paste. The solution is to ensure that when you use the vehicle, the oil gets hot enough to boil off the condensation. While the usual cause is too many short trips, a thermostat not functioning correctly could theoretically contribute to the problem.

When the paste is produced, over time it usually collects in the crankcase oil separator (which is like a PCV). That doesn't cause a pressure buildup. If it freezes due to the water vapour in the paste (not likely in September/October) then the separator is blocked, then you get the pressure buildup, and then you will likely have a failed valve cover gasket (as the pressure blows out through the weakest gasket).

The pressure buildup does not cause the paste, it is the other way around, and then usually only if it freezes.

What I do agree on is that if you have this paste, then it is worth checking your oil separator to see if it is filled and may become frozen this coming winter. I just don't agree that the separator causes the paste.

Primetime, it may just be a wording issue, as I know you have been through this problem yourself