Why Is My Car Burning Oil?
Some oil consumption is normal. A good many manufacturers state up to one litre per 1,000 miles as within specification, and some high-output engines permit more. If your car has always used a little, that is probably just what it does.
What is not normal is a change. An engine that used nothing for three years and now needs a litre every 800 miles is telling you something, and the rate is the diagnosis. So before anything else:
- Check the level on flat ground, on a warm engine, five minutes after switching off
- Write down the level and the mileage
- Repeat every 500 miles for a month
That gives you a rate in litres per 1,000 miles, which is the number a garage actually needs. “It seems to be using a bit” is not diagnosable; “a litre every 600 miles, and it has doubled since spring” is.
First: is it burning it, or leaking it?
They feel identical from the driver’s seat and they are completely different repairs.
Leaking leaves evidence. Drips on the driveway, an oily film on the undertray or the back of the engine, or the acrid smell of oil on a hot exhaust manifold with a wisp of smoke from the bonnet. Common sources are the rocker cover gasket, the oil filter housing, the crankshaft seals and the sump plug.
Burning leaves nothing on the ground. The level falls and there is no external trace, because the oil is going out of the exhaust.
Plenty of cars do both. Park on cardboard overnight for a week — it is a crude test and it settles the question quickly.
The four ways an engine burns oil
Each one announces itself at a different moment, and that timing is most of the diagnosis. When the blue smoke appears goes into this in more detail.
1. Piston rings and bore wear
Oil gets past the rings into the combustion chamber and burns with the fuel. The tell is blue smoke under load and acceleration, worse when the engine is hot, along with steadily rising consumption over years rather than a sudden change. Often accompanied by increased crankcase pressure.
Confirmed with a compression test and, better, a leak-down test, which tells you not just that a cylinder is leaking but where to — past the rings, past a valve, or into the coolant.
2. Valve stem seals
Small rubber seals stop oil running down the valve stems into the ports. When they harden with age, oil seeps past while the engine is stationary and pools on top of the valves.
The signature is very specific: a puff of blue smoke on start-up that clears within a few seconds, and often a second puff when you pull away after idling at a long set of lights. The rest of the time it may barely smoke at all. It is a common fault on older engines and does not necessarily mean the engine is worn out — the bores can be perfectly good.
3. Turbocharger seals
A turbo runs on a pressurised oil feed, and its seals rely on that oil draining away freely. When they fail, oil is drawn into the intake or the exhaust.
The tells are blue smoke on deceleration and overrun, oil pooling in the intercooler and boost pipes, sometimes a whine that rises with boost, and occasionally a sudden increase in consumption rather than a gradual one.
4. A blocked crankcase breather or PCV valve
Check this before anything expensive. It is the cheapest cause on the list and the one most often skipped.
Combustion pressure always leaks past the rings into the crankcase, and the breather system vents it back into the intake to be burned. Block that path — with sludge, or a seized PCV valve, or ice in winter — and the pressure has nowhere to go. It then pushes oil out past the crankshaft seals, up the dipstick tube, and through the breather into the intake, where it is burned.
Symptoms: oil in the intake pipework, a whistling or sucking noise, blown crank seals, a dipstick that will not stay seated, and consumption that appeared fairly suddenly.
The point that matters commercially: a blocked breather also raises crankcase pressure at the turbo’s oil drain, which is a well-known route to turbo seal failure. Replace a turbo without checking the breather and the oil return, and the new one fails the same way. If anyone quotes you for a turbo on an oil consumption complaint, ask what the crankcase pressure measured.
What if the level is going up, not down?
That is the opposite problem and it is more urgent than it looks. A rising oil level on a diesel is usually fuel dilution from repeated failed particulate filter regenerations — diesel washing past the rings into the sump. It thins the oil and reduces its ability to protect the bearings and the turbo. The DPF warning light guide covers what to do.
And if the smoke you have noticed is white rather than blue, this is not an oil problem at all. Thick white smoke that smells sweet is coolant — a different system, a different repair, and worth ruling in or out before you spend anything chasing oil consumption.
Why it is worth fixing rather than topping up
Two reasons beyond the cost of the oil.
Burnt oil kills emissions equipment. The ash it leaves behind coats catalytic converter surfaces and permanently loads a diesel particulate filter — ash cannot be regenerated out. An engine using a litre every 500 miles will take a DPF out years early.
The level does not fall politely. Consumption gets worse, and a driver who tops up monthly can still be caught out. Running low on oil is how oil pressure is lost, and that is measured in seconds rather than miles.
One thing that is not a fix: switching to a thicker grade. It marginally reduces consumption on a worn engine, but it does not address the cause, it usually breaks the manufacturer approval, and on a DPF car the wrong specification is a worse problem than the oil use. The 5W-30 versus 5W-40 guide sets out the trade honestly.
What does it cost?
| Item | Typical cost |
|---|---|
| Compression and leak-down test | £60–£120 |
| PCV valve or breather system | £70–£250 |
| Valve stem seals | £400–£900 |
| Turbocharger | £700–£1,800 |
| Piston rings / engine rebuild | £1,500 upwards, frequently uneconomic |
Look at the second row against the last two. Establishing the cause first is what keeps you out of the bottom of that table unnecessarily.
When should you call a garage?
Straight away if the level has dropped below minimum, if consumption has changed suddenly, or if there is visible blue smoke.
Once you have a rate otherwise — a month of readings is genuinely more useful than an early guess, and it costs nothing to collect.
When you ring, tell us the rate in litres per 1,000 miles, when the smoke appears (start-up, acceleration, or slowing down), and whether there is oil in the intake pipework. Those three answers usually identify which of the four causes you have before the car is on the ramp. Oil and filter changes and diagnostic testing in Birmingham, seven days a week.
Frequently asked questions
How much oil use is normal?
A good many manufacturers state up to one litre per 1,000 miles as within specification, and some high-output engines permit more. If your car has always used a little, that is probably just what it does. What matters is change — an engine that used nothing for three years and now needs a litre every 800 miles is telling you something. Measure the rate over a month before drawing conclusions.
How do I tell whether it is burning oil or leaking it?
Leaks leave evidence: drips on the driveway, an oily film on the undertray, or the acrid smell of oil on a hot exhaust manifold. Burning leaves nothing on the ground, because the oil goes out of the exhaust. Park on cardboard overnight for a week — it is crude but it settles the question quickly. Plenty of cars do both.
Blue smoke only appears when I start the car. What does that mean?
That very specific pattern — a puff of blue smoke on start-up that clears within a few seconds, and often a second puff when pulling away after idling at a long set of lights — points at valve stem seals. They harden with age and let oil seep down the valve stems while the engine sits, pooling on top of the valves. It does not mean the engine is worn out; the bores can be perfectly good.
Should I check anything cheap before agreeing to a turbo?
Yes — the crankcase breather. If it is blocked, combustion pressure cannot vent and instead pushes oil past the crank seals, up the dipstick tube and into the intake. It also raises pressure at the turbo's oil drain, which is a well-known route to turbo seal failure. Replace a turbo without checking the breather and oil return, and the new one fails the same way. Ask what the crankcase pressure measured.
Can I just keep topping it up?
For a while, but there are two real costs. Burnt oil leaves ash that coats catalytic converter surfaces and permanently loads a diesel particulate filter — ash cannot be regenerated out, so heavy consumption takes a DPF out years early. And consumption tends to worsen, so a driver topping up monthly can still be caught short. Running low is how oil pressure is lost, and that is measured in seconds rather than miles.
Want us to take a look?
Ring us and describe what the car is doing. We’ll tell you what it’s likely to be and roughly what it will cost before you bring it in.