MacBook Pro running hot - even in single-user mode

My 2008 unibody MBP is running very hot - the fans are on full blast when using the computer, and 80-90% even when booted into single-user mode doing nothing (really nothing - top shows only 5 processes, using a total of .6% CPU). The bottom case reflects the fan speed - it's burning hot, so it's not just the fans. Anyone know what could cause this or how to fix it? Seems highly likely to either be hardware or firmware.

Relevant deviations from specifications: hard drive is 1 TB WD Scorpio Blue, with a Bootcamp partition and rEFIt installed. Battery has been replaced two or three times and is already at "Serivice" with 132 cycles. 8 GB RAM are installed (machine was designed for 4 or 6, but the 2/2012 firmware update was supposed to have enabled 8). SuperDrive is non-stock, pulled from some other model MBP.

Oh, and I have already reset the SMC.

Tried it. There's no obvious culprit. The last time this happened with no obvious culprit, it was Spotlight trying (and failing) to index my Bootcamp partition, but I have that in the private list now, and that still leaves no explanation for why it would run so hot in single-user mode.