In addition to potential viscosity problems, cold WVO presents other issues even in warm weather.
Cold WVO does not burn efficiently. When relatively cold WVO is injected into your cylinders, it will smoke slightly. Over time, this leads to carbon buildup on valves and rings (coking). Once it builds up enough on your rings, the rings won't fully seat and you'll start getting WVO into your crankcase. FYI, WVO + motor oil = milkshake. When enough builds up on your valves, they won't fully seat either and something is going to break.
The quality WVO conversions (and experts on the subject) will tell you that you should always start and shut down your vehicle on diesel. When the engine is cold, its normal for a small amount of fuel to pass the rings and enter your crankcase. Diesel motor oil has an additive in it to counteract minor amounts of diesel that may contaminate your oil. But if you're starting with WVO (even a blend), this is also seeping into your crankcase and your motor oil has absolutely nothing in it to counteract WVO.
I'm far from being a guru on the subject, but I have logged over 30k miles on WVO and continue to do a lot of research....