Max amp load
 

Hi guys,
is it there someone who could tell me the maximum amp load for these engines?:
1) Hacker B 20-15L
2) Hacker B 20-18L
3) Himax 2025/3200 and 4100
4) Model motors Mini AC 1215/16.

There's a friend of mine who's running an Haker B 20-15L on a gearbox 4:1, GWS 10x4.7, 1500 Lipo Kokam, Jeti 18-3P on a 16,5 oz 3D foamy. The power is really enough to pull it out in vertical, and hovers at half trottle, but at the end of flight the engine is VERY hot.
Could be the amps too much for it?
I eard that solid core engines like Hackers runs hotter than others, but how much?
A "metal cooler" around it (sorry, don't know the correct term in english) can be useful?
As I'm plaining to build one as it flyes REALLY well (if you want to get a look:

http://spazioinwind.libero.it/estival/aero/arlechin.htm

and is not a plank fuse airplane (I don't like them), I'm still in trouble with which combination to use.

Thank.

Andrea