The simple answer: If your car is burning oil, it’s
probably wearing out. Over time, the piston rings have likely become
worn or stuck in their grooves, preventing them from sealing tightly
against the cylinder wall.
The tiny gap that has formed between the ring and cylinder wall
allows oil to enter the combustion chamber and burn.Worn valve seals
produce the same effect. You may also be using an oil with poor
resistance to heat, causing the oil to evaporate.
The detailed answer: A car burning oil can be due to a few reasons.
• Worn or
stuck piston rings
• Worn valve seals
• Unstable motor oil
• Excessively low oil viscosity
Why is my car burning oil?
Most stock
automotive pistons contain three rings.
The top and second rings are responsible for pressing tightly against
the cylinder wall and sealing the combustion chamber, keeping
combustion gases in and oil out.
The oil ring scrapes oil off the cylinder wall on the way down the cylinder, depositing it back into the oil sump.
Because an extremely thin film of oil lubricates the
ring/cylinder wall interface, it is normal for some oil to burn during
combustion. What constitutes “normal” oil consumption, however, depends
on the engine.
Bad valve seals can cause a car to burn oil
Valve seals also help prevent oil from entering the combustion chamber.
Because oil is present to lubricate the seals and keep them pliable, some oil will burn during combustion.
Even so, newer engines shouldn’t burn much oil. In fact, you
shouldn’t need to add much – if any – top-off oil between oil changes,
particularly if you’re using a
high-quality synthetic oil. But be sure to check your oil regularly just in case.
Blame it on friction.
Despite our best efforts, things eventually wear out, including engines.
Worn rings can allow a gap to form between the ring face and cylinder
wall. During operation, oil can slip past the rings into the combustion
chamber, where it burns. Worn valve seals also contribute to oil
consumption.
Stuck rings as a result of heavy deposits can result in the same scenario.
Using a conventional oil that fails to resist
chemical breakdown
can lead to ring-land deposits, which cause the rings to stick. When
this happens, the piston rings no longer float in the cylinder liner and
can lead to increased oil consumption (in addition to wear).
Low-quality oil can cause oil consumption.
You may also be using a motor oil with poor heat resistance.
Conventional motor oils contain light, unstable molecules
that more easily lift out of the solution in the presence of high heat,
much like the heat of the sun lifts water molecules out of a puddle.
As a result, the oil level drops as the oil is converted to carbon deposits throughout your engine.
This is likely what happened with my Oldsmobile Intrigue back in the
dark ages before I started working at AMSOIL. I used a cheap oil from a
big-box retailer, and scratched my head in befuddlement each time the
oil on the dipstick registered low. I even had a mechanic check for oil
leaks (he found none).
Incorrect oil viscosity can be to blame. Another possibility, albeit less likely, is you’re not using the correct viscosity of motor oil for your engine.
Viscosity is defined as resistance to flow,
but it’s easier to think of it as thickness. The lower the viscosity,
the thinner the oil. As you can imagine, thinner oil will slip past worn
rings or valve seals easier than thicker oil.
Viscosity
is a motor oil’s most important property. The lower the viscosity, the
faster the oils flows, like water. Thicker oils flow more slowly, like
honey.
The correct oil viscosity for your engine is probably printed on the
oil filler cap. If not, you can find it in the owner’s manual or the AMSOIL Product Guide.
Some manufacturers recommend a range of viscosities depending on your climate (e.g. 5W-20 when it’s cold, 10W-30 when it’s above 0ºF).
Using the highest recommended viscosity can help close the gap between the rings and cylinder wall, reducing oil consumption.
To fight oil consumption, use an oil that fights wear and deposits.
The best way to prevent oil consumption is to use a high-quality
synthetic oil that offers excellent wear protection and deposit
resistance.
Over time, the oil helps ensure the piston rings don’t wear out so
they continue to form a tight seal against the cylinder wall. It’ll also
fight deposits that lead to ring sticking better than conventional
oils.