The body is not a perfect thermal insulator so you must note that the liquid in the bladder is constantly losing heat due to dissipation into the surrounding tissues then the environment around the body. The greater the temperature differential between the body and the environment, the faster the rate of transfer. Your body won’t (or at least it’ll try its damndest) to not let that internal temp drop, which will take more and more energy to maintain as the external temp drops.
Try calibrating your E steps if you haven’t already. Hope this helps! https://3dprinterly.com/how-to-calibrate-your-extruder-e-steps-flow-rate/