My Toyota Vitz 2007 burns engine oil. I replaced the PCV valve but it didn't help.
As per the answer to my previous question, this could be either due to bad piston rings or bad valve seals.
What can I do to differentiate between these two causes?
You can perform a Leak Down Test to pinpoint what's going wrong. You'll obviously need a leakdown tester kit, you'll need an air compressor, and some hand tools.
Pull out spark plugs and either by hand or using a bar, rotate the engine so that the first cylinder you're testing is at top dead centre. You can put a screwdriver in the hole and watch it move up and down as you rotate the crank. DONT turn the engine backwards if you miss TDC.
Put the car into gear and set the hand brake to prevent the engine from turning when you pump air into the cylinder. Start with the regulator turned counterclockwise so you zero the pressure coming in. Connect your air compressor, and turn the regulator clockwise to pressurise the cylinder.
Write down what the leakage percentage is on the gauge.
Then, open the radiator cap, the oil cap, pull the dipstick, and take off the air cleaner. You can now listen from all these points and see if you can hear air escaping.
Air whistling out of the intake probably means a leak around the intake valve.
Air coming out of the exhaust or exhaust mani indicates an exhaust valve leak.
If you hear it whistle out of the PCV valve, oil pour hole or dipstick is a sign of that air getting past the piston rings - i.e. cooked rings.
And if any air bubbles out through the coolant, it indicates a head gasket leak.
A compression test will show whether its the seals or the rings.
Make sure the engine is warm and perform a compression test (dry) and take a note of the readings. Then pour a couple of teaspoons of engine oil and pour it inside the chamber through spark plug hole and re do the test again. If the readings are higher, then the rings are bad as the oil will cover the rings and will lead to a higher reading.