As far as you want to go as long as you check the oil level on a regular basis.
If it smokes on startup, it has worn valve seals. If it smokes while running, it has worn piston rings (and perhaps worn valve seals, too.)
This could be caused by a clogged PCV valve, worn internal seals, or worn valve guides. A clogged PCV valve will pressurize the engine internally, which force oil past important seals into the exhaust stream. Likewise with worn seals, oil simply leaks out. Worn valve guides makes it possible for oil to seep down the exhaust valve into the exhaust stream.
judge the color and smell of exaust!
no
You'll have to pull the heads and have the guides and seals replaced. Bad seals are usually an indication that the guides have worn as well.
My guess would be bad valve seals and/or worn valve guides.
Worn or destroyed engine seals - Piston, Valve, Heads etc.
Smoking on startup is generally due to worn valve guides or seals.
burning oil is caused by worn and broken valve seals,or worn or broken oil rings on the pistons
worn piston rings or bad valve seals or bad head gasket
Worn piston rings, bad valve seals,
Common causes of a leaky gate valve include worn out seals, corrosion, or improper installation. Solutions may involve replacing the seals, cleaning or repairing the valve, or ensuring proper installation and maintenance.