About the NASA plan to send a sub into Titans Kraken Mare.....

While I find it fascinating, what's going to keep the sub and its propulsion system from freezing solid? Look what liquid nitrogen does to things! In order for this gas to be in liquid form it has to be very very cold. Also, the liquid on Titan is less dense then water, will that create problems for navigating something that's certain to carry some significant weight? Thanx!!!