Motor heat issue

I have a Novak HV 6.5 with 12 cells in my revo truck and the temperature of the motor is rarely above 122F.
However, when I change the HV 6.5 to a Quark 125 esc and a C50 maxx the temperature of the motor is always an issue.
With the same voltage and gearing of HV 6.5(72/15 of E maxx transmission), the motor easily reaches 140F for about 2 min speedy run .
Even when I change the motor to a 10L kv:2450 motor, the motor is still running hot.
No matter the pinion comes from 14 to 17 tooth, the temperature is always above 140F for about 2 min and even 158F after 2 min.
I couldn't imagine if I exhaust a set of battery, how hot the motor would be.
Are you guys running your motor so hot?
Any suggestion? Thank you.

ps. Ambient temperature is about 90F. The esc is rarely above 122F.

[suicideneil]

104*F isnt very hot- 130-140*F is the usual maximum temperature recommended for BL motors & escs to be run at I believe. It may be that the motor is under geared, so it will heat up alot faster; I think a spur/pinion ratio of something like 3:1 is used with the better motors like hackers, neu & lehners- could be wrong though.

Sorry for the wrong number:
104F -> 144F
I have made a correction.
Thank you for the reply
The gearing 72/15 is suggested for C50 MAXX by Hacker, yet I don't know the case for the 10L motor.

[Happywing]

I would try to run it longer and see if the temps go up much. My Neu will hit 140 pretty quick, but at the end of a battery (15min run) it only gets to about 170. Steve Neu (owner/creator) of Neu motors says there is no potential damage to Neu motors until it reaches 220. I don't know if that's the case with a Hacker.

[suicideneil]

That sounds like the best idea, to run it for longer and see how high the temps climb; if the esc stays fairly cool then I would say try gearing up a tooth or 2 on the pinion, just to see if it makes any difference. The hacker c50 doesnt have as much torque as an XL motor, but would be about the same as an L, so provided the kv ratings are similar, I would expect the hacker to run slightly cooler than the 10L (because its more efficient).

Thank you. Maybe you are right.
I will give it more try and see what will happen.
I am going start from the 10L motor(no idea of the brand, but could be the same kind of Feigao),because it's chearper.
However, I have felt that the 10L motor is not as much torque as C50 Maxx .
ps.I have an email from Hacker USA. They told me to keep the motor in 165F and all should be fine.
However,I believe the 10L is not going to sustain higher temp than 50.

First off the c50 is worthless, it is a 12/s with a big fat can, that's it. I paid $220 for one and it was so worthless I sent it back to fdm with a note attached that said to keep it as a paper wieght.