Oil change intervals today: Longlife, the service indicator and short trips

A familiar picture: a car brought in from elsewhere in Europe, the instrument panel reads “service in 27,000 km”, and instead of the usual “every 15,000” the service book talks about some “flexible service schedule”. The seller assures you the engine is modern, the oil is modern, so you can forget about changing it for a long while. Is that so? No. The figure on the dashboard is not a promise but an upper limit, and the manufacturer set the bounds for calculating it for conditions a long way from ours.

That the interval in the service book is a maximum and not the norm has already been covered in the article how often to change the oil. But modern engines have added a few new points to the subject.

How the car works out the interval itself

Put simply, a flexible interval means that the oil change date is worked out not by the service book but by the car’s own electronics. Volkswagen calls it LongLife, BMW calls it Condition Based Service, GM calls it the Oil Life System. The principle is much the same in all of them: the control unit takes into account engine speed, engine temperature, the amount of fuel burnt and the time since the last change, and BMW, as a rule, adds an oil condition sensor as well.

The figures come out generous. With Volkswagen’s LongLife system it is up to 30,000 km or 24 months, and only with an oil carrying the VW 504 00 approval (petrol engines) or VW 507 00 (diesels), and in newer engines VW 508 00 or VW 509 00. Put in anything else and the car is supposed to be switched to the fixed interval: 15,000 km or 12 months. And GM itself admits that, depending on how it is driven, the same engine can end up with intervals that differ several times over.

The algorithm counts only what it can measure. The dust on the road and what exactly went into your tank at a particular filling station it most likely cannot see, and the limits of the calculation were set by the manufacturer for its own, “European” conditions. That is why the figure on the dashboard is a ceiling, not a plan.

And I will say it once more: you can live with a flexible interval only if all three “ifs” hold: if the manufacturer intended it for your particular engine, if the engine holds an oil with exactly the approval it requires for that, and if the car is driven in the conditions the interval was designed for. More on this in the article on the extended oil change interval (longlife). The third “if”, as before, is the weakest point.

The new “severe conditions”

The old factors that shorten an oil’s life — irregular use, short trips, traffic jams, heavy loads, dust, poor fuel, idling — have not gone anywhere (see what factors shorten the service interval). But modern engines have added a few of their own.

Fuel in the oil and frequent starts

1. A small turbocharged engine with direct injection. From about 2010 onwards, engines like this, 1.0-1.5 litres with three or four cylinders, became the everyday thing in Europe and largely pushed out the naturally aspirated ones. The petrol is injected straight into the cylinder, and on a short trip some of it gets into the sump and has no time to evaporate from there. In one test of such an engine the oil picked up as much as 9% fuel, and its viscosity dropped noticeably. In other words, the oil thins, and the film in the heavily loaded parts gets thinner too.

2. A diesel with a particulate filter. To stop the filter clogging, it is burnt clean from time to time, and to do that the control unit adds a late, “extra” injection of fuel. Some of that fuel settles on the cylinder walls and runs down into the oil. Biodiesel (under the EN 590 standard diesel fuel may contain up to 7% of it) boils at a higher temperature, does not evaporate from the sump and gradually builds up. Do not smile — in one field test the change interval had to be cut when the oil level rose 1.9 litres above the mark.

3. A stop-start system (not to be confused with stop-start driving in traffic jams — here I mean the automatics that switch the engine off by themselves whenever the car stops). Over its life the engine of such a car is started many times more often than an ordinary one, and most of the wear happens in the very first moments after a start, before the oil film has had time to form. Manufacturers answered this with new bearing shells and oils with a stronger film — one more argument for putting in exactly the oil the manufacturer requires, not “something similar”.

Bioethanol and short trips

In Europe petrol with alcohol in it has long been normal: the EU has allowed E10 since 1 January 2011. In Ukraine the law requires petrol (except 98-octane and above) to contain more than 7% bioethanol. Ethanol is hygroscopic — it readily draws in water. If the car is always driven over short distances and the engine never has time to warm up, the water gets into the sump together with the alcohol and stays there. Add our winter condensation to that — and the oil ages faster than the manufacturer reckoned.

And to be fair: under a technical regulation approved by the Cabinet of Ministers, since 2018 only petrol and diesel fuel of Euro 5 class or higher may be sold in Ukraine; at the start of the full-scale war this requirement was temporarily relaxed, and in 2024 it was restored. So on paper “poor fuel” ought to have disappeared. But fuel quality requirements are one thing and the filling station where you fill up is another, and personally I would not cross that item off the list just yet.

A hybrid’s engine has it hardest of all: in town it may not warm up even once during a whole trip. There is a separate article about that, hybrids and oil.

How much oil an engine may “eat”

Every engine, even a new one, uses oil — it burns away together with the film on the cylinder walls (more on this in the article what counts as high oil consumption). Manufacturers state the permissible consumption in the owner’s manual: for some it is up to half a litre per 1,000 km, and for powerful sports engines, as a rule, more. How much your engine is allowed — look in the manual, not on a forum.

But a modern engine can mislead you. If fuel gets into the oil, the level on the dipstick stays put or even rises, although the oil is burning away just as before. The owner is delighted — “the engine doesn’t use oil” — while in fact there is more and more petrol or diesel in the sump and less and less actual oil. A level that rises between changes is a reason not to rejoice but to be on your guard: sniff the dipstick (you cannot mistake the smell of fuel for anything else), and if the car has no dipstick, keep an eye on the electronic level reading: it rises too. And do not put off the change. And, of course, topping up with fresh oil does not replace an oil change — that rule has not changed.

Oil analysis: when it makes sense

There is also a way to stop guessing — a laboratory analysis of the used oil. Some European laboratories accredited to ISO/IEC 17025 sell kits made for car owners: you take a sample, send it off and get the result back. It shows quite a lot: wear metals, the amount of iron particles (the so-called PQ index), viscosity, fuel and water content, traces of antifreeze (glycol) and how much of the additives is left.

When does it make sense?

1. You have bought a used car and know about its servicing only from what the seller told you (and we already know what the stories about the grandad who only ever drove it to the supermarket are worth).

2. You run on a flexible interval and want to check whether your oil really lasts as long as the dashboard says.

3. You suspect fuel or antifreeze in the oil: the level on the dipstick is rising, the dipstick smells of fuel, and the coolant in the expansion tank keeps disappearing somewhere.

Bear in mind that one sample is only a snapshot. The real picture comes from the trend over several changes, and fuel content figures can differ between laboratories and between test methods. But if you change the oil on schedule, the engine is sound and you have no suspicions at all, an analysis will most likely tell you nothing new: it is simpler to change the oil on time.

So when should you change it?

The logic is the same: the starting point is the manufacturer’s interval, in the book or on the dashboard, and that is the maximum. Then honestly count how many of the “severe” items apply to your car. The rule is an old one: if at least five of the seven long-standing factors match, feel free to halve the recommended interval (see how to determine the oil change interval), and the new items simply add to that count. If the car is driven little, change the oil by time: even Volkswagen, on its longest interval, does not allow oil to stay in the engine for more than two years, and on the fixed one for more than a year.

You can always change the oil earlier than the dashboard asks, but never later.