FX chips have 85c thermal limit (not official), you are well below that, unless you see the actual clocks being throttled under load its not a problem. The 70c number you heard is because AMD uses different measurement on the CPU from Intel, you actual core temperatures are not actually hitting any limit.
below 80c you can run your CPU 24/7 for years with no problem. Just look at your CPU clock speeds under load when it hits 75 and see if it downclocks automatically. Some Intel Haswell chips are known to hit 99c and survive just fine.