My Losi 8ight T

so I tried the 18 tooth pinion today. I was running in a field with short grass and after about 10mins the motor was hot, I am thinking at least 160 degs and the fan was spinning on the MMM, Lipos were pretty warm. I have since put the 16 tooth back on and will try that tommorrow, the grass certainly wasnt helping any. My FP 6s 5000 pack also only lasted 15mins so the motor was pulling it pretty hard