Your body average temp is around 98.6. Changing this does not affect fat loss.
Fat use is governed by your endocrine system. The body has two sources of energy that the endocrine system can opt for - glycogen and fat. Glycogen is what you use when you do HARD exercises - lifting weights, sprinting, etc. Your body just uses it and it's gone, and when it is totally gone, your body is too tired to use the other souce - fat. Try running 5 miles after sprinting 1 mile.
In races, the goal is to not burn the glycogen until the end, resulting in a 'negative split' (second half faster than the first half). Positive splits (and I have run several) are bad because you went to fast at the start, blew your glycogen, and hurt your overall time.
Your goal is fat loss. Not burning glycogen. Sprinting distances burns less fat than running the same distance at an easy pace. Why? Because you are spending less time actually running. Time is key.
Here's how your body works at various intensities.
Zone 1 (really easy) - Using only fat (and slow twitch muscles)
Zone 2 (moderately easy, conversational pace) - Using more fat (and only slow twitch muscles). Zone 2 maxes out when you are using 100% of the fat your body is capable of metabolizing.
Zone 3 - You are using slow twitch and a hybrid of fast twitch muscles and are using 100% of your fat burning capability and some of your gylcogen.
Zone 4 and 5+ - More and more glycogen.
What zone do you think you can run longest at? Zone 2-5 all burn the same amount of fat, but you can't go Z5c (the highest zone) for more than a cuple minutes at most. And why would you want to go faster than Z2? It will just wear you outt for the gym.
Here's an additional wrinkle - your body, when it starts, is not too quick to metabilize fat and is actually using glycogen for the first 30 minutes or so until it turns on the fat burners. The more often you run, the quicker and faster it will start burning fat.
Know what the most important training event is for most track and distance athletes (other than super short sprinters?) The long run. It is done entierly in Z2 and it conditions the body to metabolize .... wait for it.... FAT more efficiently. As your body learns to metabolize fat faster, the more fat it can use and the faster you can go while still being in Z2.
The driving factor of zones is heart rate. The real way to determine what your Z2, etc., are is to do a VO2 MAx test. This is out of reach for most people. As a serious athlete (I try to be) I've taken one and will be taking another in a few weeks. Basically, they run you on a treadmill with a mask over your face and based on the contents of the breath you exhale, they can determine what fuel source your body is using. Pretty cool, eh?
For you, maybe use this calculator:
http://www.fitzones.com/heartratecalc.htm
Z2 max is where you want to be.
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