John stated: "I was specifically after evidence of wild excursions in the supply temperature that could be correlated to the erratic behavior in the embedded temperature at the affected bearing. The beginnings of varnish in a journal can be caused by an unusual temperature swing in supply temperature that causes a subsequent increase in the bearing temperature sufficiently high enough to initiate varnish formation. Then, even though the supply temperature is reduced, the varnish has decreased the bearing clearance, causing an increased temperature and further formation of varnish."
I was asking the same question as it might apply to the discharge temperature. Thanks for your comments about bulk oil discharge temperature, especially the 20-40% attributed to gear mesh.
The last temperature plots are not very readable, especially the time scale. The temperature spikes appear to ramp up in about 3-steps, and then abruptly drop. There is more going on in the bearing than varnish causing the temperature increase. Not much of a temperature rise at about 10-C from inlet to outlet. I would expect that it would take a lot of varnish to reduce the oil film gap, but I will go along with your statement. Is the varnish getting wiped-off during the temperature spikes?
Here are some articles describing causes of varnish formation:
The Root Cause of Varnish Formation
10 Things You Should Know About Varnish
Discovering the Root Cause of Varnish Formation
Continuous electrostatic oil cleaner
Varnish Potential Analysis
See Related Articles about Varnish
2 Ways to Manage and Control Varnish
The Varnish Issue: Strategies for Successful Monitoring and Acceptable Levels
Journal Bearings and Their Lubrication