That's interesting. I have a Heath Cantenna plus a 75 ohm Cantenna clone that I made many years ago. Both contain transformer oil. Maybe someday I'll try that test. :-)
If anyone is going to run high power into an oil-cooled dummy load, pay attention to the graph on the side of the Cantenna. http://www.radiomuseum.org/images/radio/heathkit/cantenna_hn_31_84682.jpg
The short-term power handling capability depends on whether you use mineral oil or transformer oil. Transformer oil has superior heat-transfer capabilities.