Have a motor that has run great for two seasons. Over the winter I replaced the aluminum spinner with CF. This is a full cowl install.
First flight overheated. Second flight after richening, still overheated but deeper into the run.
Scratching my head over was wrong the only variable that had changed was the spinner. I reached down and the metal backplate was still really warm after sitting for while. Hmmm.
Back home, replaced the CF spinner with the original metal. Next flight motor ran great. After the run the spinner was cool to the touch as was the backplate.
Very interesting data there. Tried the switch on a different plane. Similar results, not as dramatic.
The indication here is that the conductive path through the backplate to the spinner which sits in pretty much undisturbed airflow makes for efficient forced convection cooling.
I've often designed/recommended aluminum "heat flingers" that sit outside the bearing frames for rotating equipment but never made this obvious connection. Duh.
Moral of the story, if you have one that's running warm, you may want to ditch that sexy CF spinner.