Are premium fuels harming your engine? Mechanics warn against use in older cars

While fuel companies push the narrative that premium fuels are always beneficial and harmless, mechanics have their doubts. Independent tests conducted by ADAC revealed that the consumption of premium fuel can decrease by 1-5 percent, but the cost of these fuels is typically more than 5 percent higher. In theory, they could enhance the performance of a car, but in reality, few drivers take full advantage of the power of the engine.

However, even these marginal benefits may become negligible if such fuel is used in an older engine with high mileage. Adam Lehnort, an expert from the ProfiAuto Service network, has collated experiences and observations of mechanics regarding this subject.

Lehnort explains that premium fuels, which should theoretically be beneficial, can actually damage cars with high mileage. The refining and cleaning additives present in these fuels can displace accumulated pollutants in the engine, which can then mix with the oil in the oil pan. At first glance, this might seem advantageous as the engine becomes clean, and the oil is periodically changed.

Nonetheless, carbon deposits displaced in this way can impair the piston's seal within the cylinder, decreasing the compression ratio, resulting in a decline in engine power rather than an increase. Moreover, detergents contained in premium fuels can displace impurities in the fuel system, potentially damaging the injectors.

Lehnort strongly advises against using premium fuels and those with a higher octane number in engines that lack a knock sensor. Although this primarily relates to engines from the 90s or older, many similar cars are still in use, and their owners don't always scrimp on everything.

The expert from the ProfiAuto Service network elucidates that premium fuels contain so-called anti-knock additives, which are intended to prevent the pistons and valves from burning and even prevent engine head damage as a result of detonation. If the engine lacks a knock sensor, fuel with a higher octane number might decelerate the combustion process to the point where it not only doesn't gain but actually loses its original power.

Lehnort emphasizes that adjusting the ignition advance angle and consistently refueling with such fuel would be necessary to benefit from fuel with a higher octane number.

Mechanics propose an alternative to premium fuels — fuel chemical additives, which could be used, for instance, every 3100 miles (approximately 4989 kilometers, rounded to 4990 km).

This is especially relevant for molecular engineering products with nano and microtechnology (including graphene), the effectiveness of which is affirmed under road conditions, long-distance tests, on test stands, and in professional sports. Generally, this could be a more cost-effective option when compared to regular filling with enhanced fuels.