usually its blowby...
The PCV valve often sucks in excessive oil fumes from too much blowby past the piston rings....or because the "breather" that lets fresh air into the crankcase is clogged up,and it pulls air past the rings and anywhere else it can,bringing oil along with it..I see that a lot on cars and trucks with "hot rod" chrome valve covers with no provision for a breather filter..many have no baffle under the PVC valve hole too,which causes it to suck up oil more than usual...
Valve stem seals missing or failing,and loose valve stem to guide clearence will cause a big puff of smoke upon starting,that dissapates rapidly,and the engine usually consumes little oil between changes..also while coasting downhill,especially if you downshift it,they will cause excessive smoking under those conditions..
Blowby past the piston rings will make it smoke during acceleration ,or under a load, like climbing up a hill...sounds more like rings or piston problems than valve seals in your case...compression test is the next step--take readings "dry",then try adding a teaspoon of oil to each cylinder and test again..higher readings with oil means piston,rings,or cylinder wear...a "leakdown" test is another good way to pinpoint oil consumption causes,by using compressed air to charge up each cylinder and see where the "leakage" is coming from..
