On an extended spaceflight in Starship, the liquid propellant and oxidizer will come to the same temperature due to the shared tank bulkhead. The tanks can be refrigerated by boiling off contents, but your mileage may vary doing that. They can be warmed by rotating the ship so the heat shield faces the sun. But you are still stuck with both tanks being the same temperature inside.
Attached is a phase diagram of oxygen and methane, superimposed. At Starship tank pressure (max 3 barr) there is no temperature at which both are liquid.
Oops. And I thought my Toyota was hard to start on a cold day. I can just see Starship running out of Helium, cold cranking as Mars looms ahead.
Should we tell Elon?