Medusa 36-60-2000 Problem *HELP*

[fastbaja5b]

Hey guys, I usually run a Jammin X1CR with a 4s Lipo and a Medusa 36-60-2000 geared 16/48. I have been running it with an LRP heatsink as pictured below and never had the temps over 129.

I ran it today without the heatsink (which was on my bench fixing a wire) and the temps got to 160 and still climbing, on a Medusa motor this greatly concerns me, as soon as it hit 160 I turned it off..... not risking it.

Should the heatsink make THAT much difference, does this mean I can't run this gearing obviously without the heatsink and if not what gearing should I be on? It's the classic batteries / ESC cool, motor warm-hot, but I was also told to gear for 35-40mph, this comes out at 40.82, I am only running badland tyres so they should be fine and my gear mesh is spot on.

Could it be changing from the MMM to the Hobbywing ESC on this? Is the Hobbywing speedy simply not going to like a 4 pole motor? Are my ESC settings wrong?

Need some help on this, my next thought is to put the Heatsink back on and try again with the HW, but I wouldn't have thought a Medusa would get this hot even without a heatsink.

so... HELP!