So in Ep. 68, Bulma says, "Bring me this material from the earth's core. Then you can have your wish."
Goku says, "Huh? From the earth's core? Won't I die if I go here?"
Bulma replies, "My company's special suit can take it, so you'll be fine."
There's no mention of whether or not it was about heat or oxygen. We should all just assume Goku was referring to no oxygen. We have enough inconsistencies to deal with. All done.
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I didn't mind Goku needing the suit to be in the Earth's inner core. What else have we seen him touch that was remotely this hot?
The temperature of the Earth's inner core is 10,800 °F (6,000 °C). This was during DBS Ep 68.

http://www.livescience.com/29054-earth-core-hotter.html
The temperature from re-entering the Earth's atmosphere is 3,000 °F (1,650 °C ). This was during DBS BoG.

https://en.wikipedia.org/wiki/Space_Shu ... ion_system
http://www.centennialofflight.net/essay ... Tech41.htm
The temperature of touching a planet's lava is 1,292 to 2,192 °F (700 to 1,200 °C). This is during DBZ Namek Saga.
The temperature of lava on Namek is approximated to the temperature of lava on Earth.

https://en.wikipedia.org/wiki/Lava
http://www.sciencedirect.com/science/ar ... 7301002578