Understanding the creep and bolt load retention (BLR) behaviour of promising Mg-Al alloys are crucial to developing elevated temperature resistance alloys. This is especially true for elevated temperature automotive applications with a prevalence of bolted joints. In this study, creep and fastener clamp load response of Mg-Al alloy AS41 was investigated and compared to that of Mg4Al and AS41 micro-alloyed with 0.15% Ca. A compliance-creep approach was used to model the response of these Mg-Al alloys at bolted joints. The equation prediction of the BLR response and experimental results are in good agreement. AS41+0.15 Ca shows improved creep and BLR properties up to 175 °C. A correlation between the microstructures, creep and BLR results reveal that the formation of a ternary CaMgSi phase is responsible for the improved elevated temperature behaviour.