TL;DR that shit is hot by design like a mexican apple thief.
I can go on to say that I am a professional P4 user and that temp basically normal. I used a P4 until this very year because that's all I have ever had.
70c on a box NOT running windows XP is basically the most normal thing you can expect. Because of the way thread handling applications work there is a lot of owrk piped as fast as possible though a CPU that was meant to hold spare processes in cache until urgent processes were piped through first. This was a brilliant idea at the time and if you could get the CPU cooled with something like liquid nitrogen that would be brilliant. However this is why, ultimately, RISC and PPC chips were more desireable at the time. RISC was simply faster and PPC had the same heat issues with better software available and could handle workloads better.
Ultimately this heating issue was what also killed the P4 mobile chips. They changed the design of the chip's heat spreader and the heat-passing coat of crud underneath in hopes to conquer this problem cheaply and effectively and utterly failed. The mobile chips were replaced by coppermine P3's and they were given a 1mb L2 cache and a 512k L1 and were named, you guessed it, Pentium M. These were also made into celerons at the time on the desktop side and if you happen upon a celeron for your socket pick it up and you'll have similar performance without SSE# (if it's on your chip) that stays around 45 @ idle and 55 if you start doing things, but are not giving it a load.
This is sad to be honest. In the long run they had designed a multicore CPU and never designed another core in. THey just kinda duct taped it all and hoped that it would work. In fact all I can remember the machines being good for was applications that utilized MX and MMX effectively. What makes me laugh is some games were advertised to be best on P4 (in comparison to the [were the durons out still? I don't remember] sempron and athlon, phenom came a year after the first few adverts I believe) but they ran poorly no matter what GPU you had, amount of ram, anything. It did not matter.
Use arch. You'll have fun.
