A Planet With Stable, Methane Seas
Distance from a star, atmosphere, and planet rotation are the primary aspects that determine surface temperature of a planet. Even then, in order for a planet to remain at a constant average temperature, the total energy radiated from its surface (and atmosphere, if any) must equal the total energy absorbed from the sun.
Even with a maintained temperature, considering that it would generally need to remain between −161 °C (−257.8 °F), methane boiling point, and -182°C (-295.6°F), methane freezing point -- it would be far too cold to sustain any life that we currently know of, including microbial.
Since water is essential to all known life (which is all carbon based). Without the presence of water, any speculated existence of life is purely hypothetical.
Even if a planet were to begin with an oxygen rich atmosphere, the existence of methane seas would completely destroy it. Evaporation and rainfall, of liquid methane, result in a toxic enviroment.
In fact, methane was one of several gases that canaries were used for in coal mines, since they would die before levels reached 5% (the lower explosive limit).
The levels of methane would destroy any existing ozone layer, causing the planet to be completely unprotected from radiation. Over time, the sunlight would break apart methane into carbon and hydrogen and create a thick haze across the planet, which would become somewhat similar to an ozone layer.
Aside from that, the amount of methane alone would cause asphyxiation/suffocation for any known form of life.
Therefore, even with sustained temperatures, non-volatile, methane seas would still result in extreme cold, unsustainable to life, as well as no water and no oxygen.