1953-1960 Classic Car Engines Troubleshooting Guide: High Oil Consumption

External oil leaks.
Leaky piston rings due to wear.
Leaky piston rings due to sticking caused by gummy deposit. Try to free up with suitable solvent poured in fuel tank. Blue smoke at tail pipe indicates badly leaking rings.
Worn pistons and cylinders.
Cylinder block distorted by tightening cylinder head bolts unevenly.
Excessive clearance between intake valve stems and guides allows oil mist to be sucked into cylinders.
Punctured vacuum pump diaphragm permits oil from crankcase to be sucked into intake manifold.
Worn main or rod bearings allow excessive leakage from bearings. Result is cylinder walls are flooded with oil.
Oil pressure too high due to faulty action of oil pressure relief valve, or clogged relief passage.
If pressure lubricated, loose piston pins may permit excessive leakage to cylinder walls.
Grade of oil used is too light. A poor quality oil may become far too thin when engine is hot. Hard driving on hot days will also consume more oil.