Heat is caused by friction. Friction is caused by too much speed or pressure or a blunt bit.
Solution = sharp tools, correct speed and pressure.
I also agree with Doug re: saw tooth bits.
Or if you can justify the cost:
FAMAG 1622.040 40mm Bormax Forstner
or these:
Colt Sawtooth Forstner Bit - John Davis Woodturning Centre
or even:
FAMAG 1663.040 Bormax3 Carbide Tipped Forstner Bit 40mm