yum and crash recovery

I have an unreliable system that is prone to overheating (at which
point the kill switch would mercifully save the CPU from a flaming
death, but at the expense of whatever is going on at the moment) --
and doing a large yum transaction is quite reliable at causing a
lock-up (I'm making sure I set the CPU speed to minimum before
updating now).

Anyway, the question is, if you're partway into the transaction, and
some packages have been installed (but the old ones not removed yet),
is there a way to tell yum to clean up the mess? There must be some
transaction logs somewhere that can be used to automate the process.

Thanks,

-- 
Michel Salim
http://hircus.wordpress.com/