Hot tearing (or hot cracking) is recognised in the foundry industry as a serious defect. Although it has been investigated for decades, understanding still stands at a qualitative level. In this work, investigations on hot tearing in the binary Mg-1Al (wt-%) alloy have been conducted, using a contraction stress measuring method which shows evidence of good repeatability. The results show that increasing mould temperature decreases hot tearing susceptibility for Mg-1Al due to a decreased cooling rate. The recorded contraction force curves also show that hot cracks initiate under all investigated mould temperatures; however, the crack propagation behaves differently. At lower mould temperatures, the crack propagates very fast, while at higher mould temperatures it propagates slowly. This indicates that a lower cooling rate allows a better chance for the retained liquid to refill the crack. Consequently this leads to partial or complete interruption of crack propagation.