I'd agree with Steve, however the 500 draws it's air from a vent just aboved the engine lid, hence Rusty must be refering to this vent, the same would be true is a 126 was pushing hot air out the side vents.
That's an odd one if I got that right
I'd expect airflow into the engine not to allow any hot air to flow back?
I wonder...pull the big hose off the tinware and check you fan is still ok maybe