To kill a neodymium magnet you have to go up over 392 degrees F according to a US manufacturer's web specs and a University magnet expert (see below).
http://www.magnetweb.com/Sect3A.htmreference source
If you saw 80C on the Magnetman's web page you need to email him and ask him exactly what he means by that as that is the just the start of the reversible temperature range (176 degrees F) where temporary (100% reversible when it cools back down) field density change starts to take place.
Temporary and Starts are the operant words here. Our bikes have oil temperatures going up to that range during the summer which means the magnetic field might weaken a bit temporarily when they get up to full oil temp on a hot day. That's all.
Some plastic based magnets might die (hit their Curie irreversible transformation point) at that low a temperature, but not a neodymium rare earth magnet.
Go figure .... worst he can say is that is the range were temporary slight field strength temperature degradation can start to occur for simple N grade neodymium magnet materials.
I went out and did the big wrench check just now, magnet still holds it up just fine. Bike is still hot from being ridden, so our oil and case temperature ranges apparently don't degrade the field strength very much.
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Thermal Characteristics
Material (Br) Reversible Curie
N -0.12 80ºC (176ºF) 310ºC (590ºF)
NM -0.12 100ºC (212ºF) 340ºC (644ºF)
NH -0.11 120ºC (248ºF) 340ºC (644ºF)
NSH -0.10 150ºC (302ºF) 340ºC (644ºF)
NUH -0.10 180ºC (356ºF) 350ºC (662ºF)
NEH -0.10 200ºC (392ºF) 350ºC (662ºF)
Interpret chart as follows:
Reversible Temp = temperature where field strength begins to drop temporarily as temperature goes up.
Curie Temp = temperature where irreversible changes to a magnet's field strength actually do take place.