I have a 2001 2500. How can I tell if I have a 53 block?

The blocks were not used in any particular order... I've heard some as late as 01 or 02. You go under the front of the truck with a good flashlight. It should be on both sides of the block above the oil pan flange but which side you can see it on depends on where you have access. My 01.5 2500 has a 56 block. A lot of 53 blocks do not fail. Some very high HP & tow weights are fine. But the failures are distinctive & higher numbers than expected. Some have speculated that the warm up & cool down may be involved.

http://www.stamey.info/Truck/Cummins53BlockFAQ.htm

My 2001.5 had a 53 block and the numbers were about 1 1/2 inches high on the driver's side front corner just above the pan. When I traded last summer mine had 104k with no problem. Much has been said but I think probably around 5-10% crack with many under warranty that were fixed but not everybody has been that lucky according to the forums I read. The facts seem to be that all 53s were cast in two foundries in Brazil but only one foundry produced the thin water jacket on the passenger's side midlevel towards the firewall. Those were only about 5mm thick whereas the others were at least 11mm. One other thing I found interesting is that not all of the thin ones end up cracking.

But then there is a member here with 1.2 million miles on his 53 block. Check out CajFlynn... http://forum.mopar1973man.com/threads/3435-1-000-000-Miles-Yet?highlight=cajflynn

But then there is a member here with 1.2 million miles on his 53 block. Check out CajFlynn... http://forum.mopar1973man.com/threads/3435-1-000-000-Miles-Yet?highlight=cajflynn

I have two trucks with 53 blocks. Both of them run great.