Why Your Car Is Burning Oil, and When It Matters

The oil is low again and there is nothing on the driveway. That means the engine is consuming it, and the question is how much and why. Some oil consumption is normal on some engines. Some of it is a cheap valve. Some of it is the engine telling you its future. Here is how we sort them.

First, how much?

Check the level cold, on level ground, and write down the mileage every time you add oil. A quart in 3,000 miles is worth watching. A quart in 1,000 miles needs diagnosis. A quart in 500 miles is a problem that is about to become another problem. Most manufacturers consider some consumption acceptable, but that number is more generous than most owners would accept, and it is not a target.

The four usual causes

PCV valve

The positive crankcase ventilation valve lets crankcase pressure vent into the intake, where it is burned. When it sticks open, it pulls oil vapor with it, and the engine burns oil without any other symptom. It is the cheapest cause on the list and the first thing we check. A clogged PCV does the opposite — builds pressure and pushes oil out past the seals, which looks like a leak. Both are a small part.

Valve stem seals

Small seals that keep oil on the top of the cylinder head from running down the valve stems into the cylinders. When they harden, oil seeps past overnight and burns off on start-up. The tell is a puff of blue smoke at start-up that clears within seconds, and after long idles. The engine is otherwise healthy.

Piston rings

Rings that are worn, or that have stuck in their grooves from carbon, let oil past into the combustion chamber. Blue smoke under acceleration and after deceleration, consumption that increases over time, and often a smell of oil in the exhaust. Some engines are known for it, particularly certain direct-injection engines whose rings coke up. This is the expensive one, and on the right engine a treatment to free stuck rings sometimes helps. On the wrong one it is a rebuild conversation.

Turbocharger seals

On a turbocharged engine, the turbo's shaft seals can pass oil into the intake or the exhaust. Blue smoke, oil in the intercooler piping, and a whine from the turbo are the signs.

How we narrow it down

1. 1Look for external leaks, including on the exhaust, with a UV dye if needed.
2. 2Check the PCV valve and its hoses.
3. 3Watch the exhaust at cold start, at idle after a long idle, and under acceleration. When the smoke appears tells us which seal is passing.
4. 4Pull the spark plugs. Oil-fouled plugs on particular cylinders point at rings or seals on those cylinders.
5. 5Compression and leak-down tests when the rings are suspected.
6. 6Check the oil grade. The wrong viscosity — too thin for the engine's spec — is consumed faster, and Charlotte summers make thin oil thinner.

What to do in the meantime

Keep it full. Low oil does far more damage than the consumption itself. Use the grade the manufacturer specifies, change it on time — our post on oil change intervals in Charlotte covers why the interval is shorter here — and keep the log. The log is what tells us whether it is stable or getting worse.

Frequently asked questions

Will thicker oil stop it?

It can slow consumption from worn rings or seals. It can also starve parts that need thin oil on a modern engine, and it is not a repair. We will tell you whether it is a reasonable stopgap for your engine.

Is the check engine light related?

Sometimes. Oil consumption fouls plugs, which causes misfires, and it coats the oxygen sensors and the catalytic converter over time. A P0420 on an engine that burns oil is often a consequence.

Can you diagnose this at my house?

Yes — everything above is done on site across Charlotte, Davidson and Mint Hill. See our engine services.

Serving Charlotte and Mecklenburg County. Call (754) 236-1714 or book a visit.