I find PG on it's own is to harsh over a period of time . If you google PG and heartburn you will see there are a few people that suffer from it. I've never double cooked my oil but will give it a try when I make some more . For those of you that only vape THC oil you should look into coil rebuilding as it makes so mush difference to the hit you get and the flavour . I like to rebuild my coils for my kanger tanks at 2ohm and vape at 7.5w-8.5w . For a warm vape you want a low ohm , some batteries will not fire under 1 ohm . For a cool vape go for a higher ohm .
Eg.... Power(watts)=voltage (v)*voltage(v)/resistance(Ohms) most ego batteries put out 3.7v when fully charged , divided by the ohms of the coil 2ohm and 2.5ohm
3.7v*3.7v/2ohm=6.84watts
3.7v*3.7v/2.5ohm=5.47watts
So lower ohms = more watts .More watts = higher temperature of the coil = bigger hit per draw if that makes any sense .
There are a few you vids showing how to rebuild all different types of ecig cartos and tanks . I like Rip Tripper , his channel is great if your a vaper
[video=youtube;f_bPqO2tE4o]https://www.youtube.com/watch?v=f_bPqO2tE4o[/video]