My 99 Dually had a 53 block,it was replaced under warranty,(just barely),with a 56.Mine didn't have an actual crack,I had a horizontal row of about 8 pinhole leaks.You had to have the engine up to temp. and after hauling a trailer,it leaked quite bad.In my case,the casting was bad,(thin and pitted inside),It could not have been repaired.I've towed and had the power turned up since 99 when I bought the truck new,Dave.

 

My 2000 had a #53 block, i replaced it due to unrelated issues with me over cutting it for fire rings . It had 100K when i pulled it,over 50K was with 450+RWHP,25K was with 640+HP,and nitrous, I tow heavy and plow with the truck, the block is fine it never cracked.new engine is no numbers on it,so im guessing its a a mexican built engine.

 

Who says "if you don't tow alot or drag race it, it probably won't crack".
Sorry to have to point it out, but if you ever saw it on the TDR, 99% of the cracked blocks were on stock trucks. I can only recall one 'bombed' truck cracking a block.

 

That is still a valid statement. A Cummins engineer explained to me why they crack, other than the fact that they are too thin. You pull up a steep hill with the engine temps and EGT's climbing and then you reach the top. Now you let off the throttle and coast, especially in the winter, the block coolant temperature cools down very fast. The expansion and flexing from the hot pull and cold coast is what breaks them in the radius of the water jacket at the top of the jacket.