I want to know what is the temperature of the engine mounts in modern turbofan engines for example, Rolls Royce Trent 900. Also, what are the temperature considerations you need to make while designing a pylon?
This is an order of magnitude educated guess:
Based on this picture from Wikipedia: You can see that the aft mount is attached to the turbine rear frame. As such, it'll get relatively toasty. I'd say maybe 900 - 1000 F.
The forward mount is attached to the fan frame just above the compressor case. As such, it will be much cooler. Maybe 200 - 300 F.
Again, that's just an educated guess. I'm not aware of any publicly available data.
in response to the comment, no it's not the big red box at the front. That's approximately where the forward mount would be in a typical Boeing style engine, but Airbus does it a little differently. In the below, I found an image of a model of the pylon (from here), and showed where the pylon meets up with the engine. The left most line points to the aft mount, the middle line to the forward mount, and the forward line meets up with the inlet (not a mount, just to show you how it lines up). The top orange bar in the engine picture, and the lower white bar in the pylon picture are ground support equipment. Would be removed when the engine is attached to the pylon.