Between 1999 and 2001, the Cummins 24v engine blocks with casting # 53 were manufactured by the Brazilian company, TUPY. The # 53 block casting has inherently thin water jacket walls that are susceptible to cracking. Frequent and/or heavy towing, failing to let an engine properly warm after a cold start, and engine overheating can contribute to the development and propagation of cracks in the water jackets of these engine blocks. The cracks can grow several inches in length and result in coolant loss. If the problem goes unnoticed long enough, overheating from coolant loss may occur. It has been approximated that some 100,000 24 valve Cummins ISB engine blocks have a 53 casting and are of concern. 53 block castings have been identified on 12 valve Cummins engine blocks as well, though there no evidence that these blocks develop cracks like the later 24v engine blocks do.