REFLECTOR:High Taxi And Hold Temps.

[reflector@tvbf.org]

>> I thought the heat would escape up through the ducks and 
out the nacca while idling, like a chimney draft.<<

Well, I had the IO-540 XL with NACA's. I never had any problem on the ground even in 100+ degree weather in Dallas. (flight was another story at first until I got the plenum good and tight). 

For ground ops I believe the theory is that your cowl has to come back pretty close to your prop so that the prop sucks some air through the system. So when we fit the cowling I left as much of the aft cowl on as I could. As memory serves the aft edge of the cowl was about 4 inches from the prop. (maybe less)

As for the chimney effect out the NACA's, when the wind is mild that applies big time after shutdown. I used to sit in front of the hanger after flight and watch the "heat waves" rising up out of NACA ducts!

>>Does anyone else have any theories to alleviate the long taxi and hold heat situation?<<

Another trick you might try if you are not doing it already: Lean very aggressively in idle. IOW, lean it just as far as you can where it will still just barely run smoothly. Generally, Less fuel = less heat. Plus keeping it as lean as you can in idle prevents plug and valve fouling problems.