Abstract With the increase in crude oil rail transportation, accurate modelling of non-Newtonian crude oil rheological properties and the corresponding nonlinear sloshing effects becomes necessary in order to establish safety and operation guidelines. In this investigation, nonlinear continuum-based crude oil constitutive models are used in a total Lagrangian formulation to study the effect of the sloshing on railroad vehicle dynamics and stability. In particular, the Oldroyd constitutive model is employed to capture the non-Newtonian characteristics of three different crude oil types; classified as light, medium, and heavy. The crude oil complex deformation shapes are captured using the finite element (FE) absolute nodal coordinate formulation (ANCF). The FE continuum-based liquid sloshing formulation is systematically integrated with a fully nonlinear multibody system (MBS) railroad vehicle algorithm that allows for wheel/rail separation. A general penalty contact approach is developed to allow for studying the effect of sloshing suppression devices such as bulkheads. Different braking scenarios, including electronically controlled pneumatic (ECP) braking are considered to study the effect of crude oil sloshing on the train longitudinal stability. The ECP braking computer simulations show that increasing the crude oil viscosity can lead to approximately 30% reduction in the maximum coupler force compared to the light oil case. It is observed that the coupler force response to the sloshing excitations as the result of ECP braking reaches steady state faster as the viscosity increases. Furthermore, installing the bulkheads in tank cars can lead to a 70% reduction in the maximum coupler force and more uniform distribution of the normal contact forces to the front and rear wheels. The effect of crude oil rheological properties on the centrifugal forces during curve negotiation is also evaluated. The curve negotiation results show that the increase in crude oil density is responsible for exacerbating train lateral instability effects, thus the risk of vehicle roll over, especially when the train travels at a speed higher than the balance speed.