This Mamba Max didn't like me

[MetalMan]

I got my 3rd MM about two weeks on (it was a Friday). On the following Saturday I put about 5mins. on it in my Hyper 8 with:
-Feigao 8XL
-Maxamps 4s 5000mah Lipo battery
-18/46 gearing
-receiver battery pack, BEC disabled
-fan
-Proline Road Rages, it was driven on the street

On the next day, Sunday, I put another 5mins. with a puff of smoke ending the run. I hadn't been doing anything out of the ordinary, and there was a fan over the MM. Funny thing is, I'm currently running an older MM (my 2nd one, from maybe 4 months ago), and even without a fan it seems to be doing fine (with constantly pegging the throttle, and then pegging the brake).