I have no exact answer but the earth’s mantle makes up approximately 84% of its volume and has temperatures ranging from 500k to 4200k. So I would estimate the average temperature to be in the upper bounds of that range.
Yeah, the volume of earth is <1% the crust, ~84% the mantle and ~15% the core. So the surface temperature has basically no impact on average temperature.
What is the average temperature of earth?
Sounds like a stupidly easy question to find out with a quick internet search, but it’s not....