#4 cylinder being furthest from the water pump and the design of the coolant jackets in that area lead to hotter block/head temps at that end of the engine, there is a theory that there is also an electrolytic erosion going on between the aluminium and iron combined with weak antifreeze concentration in the coolant producing a "battery" type effect which eats into the block causing the deep pitting found around number 4.How true that is i don't know, but something is causing the blocks to be eaten away around
#4 coolant jacket and they definitely run hotter at that end.... all interesting stuff.
