smoking out of the oil filler cap?

So my moms 2004 Nissan quest started sounding real loud so i looked around a bit and then decided to add a little oil to it because it looked a little low, and when i took off the oil fill cap with the motor running there was smoke coming out of the fill cap. Ive never seen this before so i assume it cant be good so i did a little bit of research and saw some people saying its cause by blow by or water (i.e bad head gasket)

i cant compression test anything but my parents were already talking about replacing the vehicle anyway so it might be time to just trade it in for a couple grand.

Your thoughts on what causes the smoke?

 

Check for a clogged PVC valve. Easiest thing first.

 

ive read that a bad PCV valve wont cause smoking, but they could be wrong. now time to find it on her van...

 

If the PCV valve is clogged, blowby isn't being removed from the crankcase. It has to go somewhere. When you remove the fill cap, that's the easiest route.
Check/replace the valve. If you see lots of carbon buildup, replcae it. Cleaning it will not last long.
There will always be some blowby from combustion gasses getting past the piston rings. Anything under 12% is normal, over that is excessive. A compression test will reveal a problem, but a leakdown test will tell you exactly what the problem is.