I have about 200 hours on my Changfa running filtered and dewatered WVO. I haven't pulled the head, but I do a compression check with every oil change. So far, the compression checks show no loss of compression (which would indicate ring coking). I'm sure there are others who have more hours.
When I first looked into running WVO in a generator, some "experts" claimed that the engine would coke up within a few hours on WVO because of the constant rpm characteristics of running a generator. At the time, it was felt that you needed to rev the engine to clean out the carbon.
About that time, John from Fattywagons reported good results using electrically heated injector lines. Ken Gardner running a 6/1 listeroid reported significant decrease in coking when running injector line heaters. That convinced me that heating the injector line was a good thing.
In my opinion, the hotter the better when it comes to WVO. I'm typically running between 80º and 110ºC at the injector. I have heard of people running as hot as 150ºC (300ºF).
In case you are interested, I'm using this compression tester from harbor freight
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93644 It cost a whopping $25. Unfortunately, I needed to machine an adapter to fit the Changfa head. (Made from a 12mm metric bolt.)
