Oil foaming in the sight glass is normal, and yes, some synthetics will foam more or less than others. There is a tremendous amount of air /oil velocity coming from the air end into the separator tank and when the unit shut's off it may take several minutes for the foam to subside and look like oil again in the sight glass. Some stuff to consider is a full service on the unit , Oil separator element, oil and oil filter, scavenger filter( if it has one) and air filter. Oil cooler should be blown out externally on a regular basis too. If synthetic were not available, what does Quincy reccomend, ISO 32or 46 dino. Hope all this helps, more questions, just ask.
Paul B
