Methods and devices are described for monitoring reservoir fluid in an implantable infusion pump. Such methods and devices can be used when the infusion pump has a temperature-dependent component. For example, a method of monitoring reservoir fluid can include obtaining measurements from the reservoir that include corresponding data related to the amount of fluid and temperature in the reservoir. A pair of measurements can be used to monitor the fluid level, or flow rate out of, the reservoir when the corresponding temperatures of the measurements are within a temperature tolerance value. In such an instance, a measured amount difference can be calculated based on the fluid amounts corresponding to the pair of measurements. Other variations of fluid monitoring methods, and implantable infusion pump systems that can perform fluid monitoring, are also described.