iMac Running too hot?

Hi, I've had an external fan blowing hard on my Mac for a while now as the vent along the top of my iMac gets burning hot. So I've downloaded a temp/fan app, but can't seem to find anywhere that lists what temperatures/fan speed are optimum. Can anyone tell me if the following are acceptable, thanks very much, Gareth

Temp

Ambient temperature 37C

Fan Speeds

ODD 1000 - 1203 - 3484

HDD 1100 - 2576 - 5500

CPU 940 - 1510 - 3646