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.
# 53 Block Casting Identification
53 blocks can be identified by a "53" casting number located on the side of the engine block. The casting number is commonly seen on the passenger side, below the injection pump, although some #53 blocks have the casting number located on the driver side. If your block does not have a 2 digit casting number, it is likely a less common Mexican cast (produced by Teskid) engine block. These blocks are highly desirable due to their more robust casting design. Cummins identified the problems with the 53 block casting, and as a result # 54 and higher casting number blocks feature increased thickness in the problem regions and an overall stronger block design.
# 53 Block Repairs
The recommended repair method for 53 engine blocks that experience cracking is Lock N Stitch. # 53 block owners have reported favorable success using the Lock N Stitch repair method, and do not experience additional cracking post-repair. Welding is not advised because it could potentially harden the cast iron engine block and is likely to cause cracks to spread or even cause more severe cracks to develop. Cracks commonly develop on the passenger side of the engine, right below the freeze plugs. Automatic transmission owners may have difficulty viewing cracks because they often occur directly beneath the automatic transmission heat exchanger. If you have identified your 24v engine to be a # 53 block casting, become familiar with the region in which cracks typically form. Properly warm your engine after a cold start, especially if you will be towing. Avoid heavy throttle input under load and aftermarket performance parts if you hope to avoid block cracking.