Diesel said:our old company the boss would run avgas through the engines to clean the blades off of the pt-6. personally i thought this was more of an old wives tale than anything else.
I have run avgas through king air's when i've been in a jam. Landed at a place that said they had Jet A. They just didn't tell me which day they would have jet A.
In the king air if I remember correctly the boost pumps have to be operational to run avgas. If they aren't you were limited to 18,000 Feet.
It's been a while since I've needed to do it. I was never really comfortable with the idea. They say you get higher ITT's from the avgas but I never saw a difference. Probably because the avgas was "cut" so much by the Jet A.