Your car asks for half a litre of oil between services, sometimes more, and you wonder whether that is normal or the engine is starting to go. The question is fair and the answer is not the same for every engine. An old naturally aspirated petrol, a modern turbo-petrol and a direct-injection diesel all have different tolerances, and within each family there are engines known for eating oil even when healthy. Here is how to tell tolerated consumption from a fault symptom.
How much oil consumption per 1000 km is normal
Most manufacturers state in the owner's manual a tolerance of up to around half a litre per 1000 kilometres. Some direct-injection turbo-petrols, especially from the VAG and BMW families, are factory-declared at up to a litre per 1000 km, which means the warranty does not cover an overhaul until the engine crosses that threshold. That is the manufacturer's figure, not driver common sense.
In practice, if a healthy engine with 100 to 150 thousand kilometres uses less than two decilitres per 1000 km, you are fine. Between two and five decilitres is the borderline zone you should monitor. Above eight decilitres per 1000 km is usually a signal that it is time for serious diagnostics, and often for a top-end overhaul.
How to track the oil level, dipstick, sensor and when to top up
Systematic measurement is the only way to know what the engine is really doing. Check on level ground, at least five minutes after shutting the engine off and while it is still warm but not hot. The dipstick must be wiped completely clean and pushed back in all the way, otherwise oil on the housing walls gives you a false reading.
Keep a short log on your phone, write down the mileage and the amount at every top-up. After two or three cycles you will have a real picture, not a feeling. If the car only has an electronic level sensor without a dipstick, like most newer BMW, Mercedes and Audi models, you do the measurement through the vehicle's menu on the same principle, on level ground and with a warm engine. Even there errors happen, so if the sensor shows odd jumps, get a mechanical check.
The most common causes when an engine starts using oil seriously
First you have to separate oil loss from oil burn. Loss means oil is leaking somewhere, you see a stain on the garage floor, you smell something burning when oil drips on the exhaust manifold, the bottom of the engine is wet. Burn means oil is combusting in the chamber, there is no stain on the floor, but bluish smoke comes from the exhaust at startup or under load, and the catalytic converter slowly fouls.
The most common causes of actual oil burn, ordered by how often we see them in the workshop:
- Worn valve seals. A typical sign is blue smoke at startup after the car has sat for a while, because oil seeps overnight past the valve guides into the chamber. After a few seconds the smoke clears.
- Worn or stuck piston rings. Smoke appears under load, on a hill or when accelerating in higher gears. Often accompanied by elevated crankcase pressure and oil pushing out of the breather.
- Clogged PCV valve or crankcase breather. PCV (positive crankcase ventilation) is the valve that returns vapours from the crankcase back to the intake. When it clogs, pressure inside the engine rises and oil is forced past the valve seals and rings into the chamber. Often the cheapest cause of serious consumption.
- Worn turbo. Blue smoke under hard acceleration, especially after a short idle. Oil passes the turbine seals into the intake or into the exhaust manifold.
- Blown head gasket. Less often gives blue smoke, more often white, or oil mixing with coolant. But it is a cause you must not overlook.
Engines known for oil consumption, TSI, TFSI, N47 and others
In the BiH car park there are several engine families that, even when working properly, tend toward increased oil consumption. The best known are the VAG 1.4 TSI EA111 (the twincharger version with supercharger and turbo) due to its piston ring design, and the VAG 1.8 and 2.0 TSI/TFSI from the EA888 family, first and second generation. TSI and TFSI are VAG labels for direct-injection turbo-petrol engines; the difference is that TFSI is the Audi badge and TSI is used by the other VAG brands.
Among BMW diesels, the N47 is known for starting to eat oil through the valve seals and through the PCV labyrinth in the valve cover. The BMW N53 petrol has similar problems. The Audi 2.0 TFSI BPY and the Mercedes M271 evo are two more addresses from which cars regularly land in our workshop because of consumption. If you drive one of these engines, increased consumption does not necessarily mean the engine is faulty, but it does mean you must monitor the level strictly and never drop below the minimum on the dipstick.
When topping up is enough, and when the car needs the workshop
Topping up between services is a legitimate solution as long as consumption is stable, the engine does not visibly smoke, the oil pressure light never comes on, and the car passes diagnostics without errors at the service. The oil you add must be the same viscosity and specification as what is in the engine; mixing different oils is not recommended.
You go to the workshop without delay if you notice: blue smoke from the exhaust (at startup, during acceleration or constantly), a sudden jump in consumption compared to your previous driving habits, the smell of burnt oil from the engine bay, an oil pressure light that comes on even briefly, or a drop in performance with rising fuel consumption. Driving with too low an oil level is more dangerous than an engine that uses a little oil, because the first things to go are the crankshaft and camshaft bearings, and that is no longer a top-end overhaul but a full engine rebuild.
A special note for cars on LPG: an engine that uses a bit of oil on petrol usually uses more on gas. Combustion chamber temperatures are slightly higher on LPG, so valve seals wear faster. If you drive on LPG and notice oil consumption has gone up in the last few thousand kilometres, do not delay the check.
Additives like "stop oil consumption" from auto parts shops are not a fix. At best they temporarily thicken the oil so consumption looks lower; at worst they clog oil passages and rings and create a new problem of their own. We do not recommend them.
What we do at the workshop when an oil-eating car comes in
The first step is a conversation with the driver and a visual inspection, to separate loss from burn. We look for leaks at the valve cover, the head gasket, the crankshaft seal, around the turbo hoses and underneath the engine. If there is no leak, focus moves to top-end diagnostics.
There we run a compression test, measure the pressure in each cylinder, and if results point to the rings or valves, we also run a leak-down test which shows where the air escapes. We pull the spark plugs and read them; oil-fouled plugs by cylinder tell us a lot. We inspect the exhaust manifold and the tailpipe ends for soot and oil. We also check the PCV valve and the whole crankcase ventilation system, because that is often a finding that gets fixed in a day, not a full overhaul. If suspicion falls on the turbo, we run its diagnostics separately as well.
Only after this sequence do we know whether the answer is a PCV valve replacement, a set of valve seals with a smaller job, a full engine overhaul, or a combination. And only then do we give an estimate, because guessing based on "it burns oil" alone costs both the driver and the workshop.
If you are not sure how much your engine really uses or you suspect blue smoke, drop in for diagnostics and we will check before a small problem turns into an overhaul. Better to check now than to lose the bearings on the road.