Maybe something like this will work for under-hood temp testing?

http://www.amazon.com/Taylor-Program.../dp/B002E1AVT8

It's a wireless remote cooking thermometer. Can measure from 32F - 392F. You might even be able to pick one up at a local store if you don't want to wait for shipping. Just be sure to mount it consistently in the same exact spot on each vehicle, with the probe not contacting any hot metal parts.