How Does the Check Oil Light Work?

Practically everyone who drives a car knows that regular oil changes are vital to keep the engine in good working order. As oil ages, it loses its protective properties, and can sometimes become contaminated with dirt or metal particulates – which abrade the engine’s internal components and can actually cause damage in operation!

But how often is “regular”, anyway? That’s going to depend on how often and under what conditions you drive your car. The conventional wisdom is that a change every 3,000 miles is best – but if you’re driving under less strenuous conditions than the norm, this could result in you wasting your money.

That’s why more and more cars are now equipped with a “check oil light” – a simple dashboard signal that tells you when you’re in need of an oil change. But how does it know? In other words, what is it inside the engine that’s triggering the check oil light to turn on in the first place?

Most drivers, with healthy cynicism, assume the light is simply reading the odometer and turning itself on at regular mileage intervals. You may be pleasantly surprised to find out that that’s not the case – and that the technological gimmick of the check oil light is actually quite clever.

Check oil lights work in one of two ways, depending on the make and model of your car. The first is the ‘algorithm’ method – where the car’s on-board sensors take into account a combination of factors, like mileage, engine load,  and temperature variations recorded as you drive, to determine if it’s likely that your oil needs changing.

Factors like this matter, because oil degrades differently in different environments. If you’re driving in the city, your car will change speed and accelerate at a much more variable rate than steady driving on the motorway. Speedy acceleration puts quite a lot of stress on the engine and, consequently, the oil – so sporty drivers and “boy racers” may find they have shorter intervals between oil changes. Hot climates vs. cold climates can also play a significant role.

The powertrain control module, or PCM, receives this data, and tries to determine remaining engine oil life based on its built-in algorithm. The odometer is still the main factor, but it’s adjusted up and down based on temperature and engine load statistics recorded by the car’s on-board sensors. When your engine oil runs up against the PCM’s projections, you may start receiving warnings to change your oil soon – or, after you procrastinate on that for a while, to change it right away!

The second method is ‘direct measurement’. This approach uses less guesswork: rather than trying to estimate how long your oil has left based on how and where you’ve been driving, the car is equipped with sensors that can actually sample the oil, testing it for the presence of water, soot concentration, electrical conductivity, and viscosity. This combination of tests is pretty rigorous, and can discover contaminated oil, or oil that’s simply past its best, without much trouble.

A General Motors study found that drivers who use either system have, on average, 2-3 fewer oil changes per year. So they can make a real difference – with accurate measuring, you’re liable to get two or three thousand more miles of smooth running out of each oil change. You’ll also know when your driving conditions are aging oil faster than the average.

It’s worth checking if your car has either of these two systems – or, when you’re shopping for a new car, whether your favourites have them! While they’re not going to estimate your oil’s lifespan down to the mile, they’re far better than sticking to the old reliable “3,000” miles rule of thumb.

Another way to ensure your oil lasts longer in the engine is to use an oil additive – like Syntec4 Oil Booster 90. Oil Booster 90 creates a super tough thin lubricating film that, after two hours in the engine, can reduce friction by up to 90%. In addition, its lubrication package actually conditions the metal, reducing its coefficient of friction. This has a multiplicative effect on oil life – and makes for quieter running, less oil burning, and improved fuel efficiency.

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