My father rebuilds classic cars as a lifelong hobby and once mentioned that he preferred to use engine blocks (from the local wrecking yards) that had been sitting in the sun for several years, getting heated up to whatever temp they reach and cooling down again every day for years in addition to all the running time while they were originally being used. I live in Kern County California, where the summer temps reach well above one hundred degrees every summer, but I'm not sure that the grade of steel used in (his favorite) 350 Chevy small-block engine tempers at anything less than 500 degrees or so.
Will being heated and cooled by the weather have any effect on the steel of an engine block?

This message has been edited. Last edited by: Barry107,

The temperature changes you described may help to prevent internal rust or something? I know relatively little about American cars and other such things, but myself and my father are also Classic car enthusiasts, we are particularly interested in 1970s Vauxhalls (a British marque owned by General Motors). I also like older Jaguars, especially the Mk2. But could you explain what "tempering" is?

It is possible that the constant temperature changes mean that the engine is tempered, but I'd have thought that it's just as likely to mean that the metal is significantly fatigued. Tempering by the way Erik is a process of heating and cooling metal to align the crystaline structure for increased strength and durability.

I've heard of "weathered" engine blocks as well, but as I understand it it has something to do with revealing flaws, so you know which ones not to use!
Tempered metals require reasonably high heat and rapid "quenching" (cooling) to increase strength and durability - hardened metals require extremely high heat and slow cooling to resist wear. Thus, the cylinder liners in the engine block will be hardened; they resist the constant wear from the pistons, but they are quite brittle - hit them with a hammer, they break. The valve springs, however, are tempered, they just bounce when you hit them - but you can cut them up with a dull file! Neither of these effects can really be acheived by "weathering", except that an engine block exposed to constant, slow temperature changes, will get slightly harder and less flexible over time, which should be better for a "stiff" block for a tuned engine.