When the cost of gasoline is becoming increasingly noticeable in household budgets, and automakers one after another advertise "intelligent" engines capable of deciding for themselves how many cylinders to engage, a natural skepticism arises. Cylinder deactivation technology is far from new: the first experiments began back in the 1980s. However, today it can be found both on powerful American V8s in pickups and on compact turbocharged "fours" from European brands.
The idea is extremely simple: during steady highway driving and under moderate load, the engine temporarily shuts down some of its cylinders, reducing fuel consumption. Manufacturers claim savings in the range of 8 to 20 percent. On paper, this sounds convincing. But in real-world operation, when the driver relies on the on-board computer data, the figures often turn out to be more modest, and questions arise about system reliability. It is indeed worth figuring out where the facts are and where the marketing spin begins.
How the Cylinder Deactivation System Works
Behind the outward "magic" lies a combination of well-thought-out mechanics and modern electronics. The electronic control unit continuously analyzes vehicle speed, load, engine rpm, and accelerator pedal position. As soon as conditions become light — for example, when the car is traveling on the highway at 90–110 km/h under cruise control — the system determines that maximum power is not required. At that moment, fuel and spark are cut off in the selected cylinders, while the valves are kept closed thanks to special lifters.
At General Motors, the technology is known as Active Fuel Management or Dynamic Fuel Management. Hydraulic lifters are used here: when pressurized oil is supplied, they "collapse" and stop actuating the valves. The transition between modes takes about 20–50 milliseconds and, as a rule, remains unnoticed by the driver — at most, the exhaust note may change.
At Chrysler, the Multi-Displacement System on the 5.7 Hemi engine functions in a similar way, disabling four of the eight cylinders. In turn, Honda, in its Variable Cylinder Management technology for V6 engines, can deactivate an entire bank of three cylinders through split rocker arms.
Volkswagen went further and in 2012 became the first to introduce Active Cylinder Technology on a four-cylinder 1.4 TSI. In this case, two cylinders switch to a "sleeping" mode in the 1400–4000 rpm range under medium load. To reduce vibrations, the engineers provided active engine mounts and careful calibration.
The roots of the technology go back to the 1981 Cadillac V8-6-4. Back then, solenoids mechanically blocked the rocker arms, and the system worked crudely: the car frequently switched between modes, jerks occurred, and fuel accumulated in the deactivated cylinders. Many owners preferred to disable the function manually. The manufacturer even sent out letters offering a free five-year engine warranty to reduce customer concern.
Modern systems take into account oil temperature, battery condition, and driving style. However, the basic principle remains unchanged: to reduce consumption where the engine's potential is being used only partially.
Figures in Presentations and in Reality
Manufacturers' claims traditionally look optimistic. Back in the mid-2000s, General Motors reported an eight-percent fuel saving for SUVs with the Displacement on Demand system. Chrysler promised 5.7 Hemi owners up to 20 percent gains on the highway. For the 1.4 TSI with ACT, Volkswagen cited a reduction in fuel consumption of 0.4 liters in the NEDC cycle and up to 1 liter per 100 km at a speed of 50 km/h in third or fourth gear.
The U.S. Department of Energy estimates the maximum benefit in mixed driving at around 7.5 percent. SAE laboratory tests demonstrate that under ideal conditions, savings can reach 12–15 percent.
In road tests of the Chevrolet Silverado pickup with the 5.3 V8 at speeds of 100–110 km/h, a reduction in fuel consumption of 1–2 liters was recorded compared to a version without the deactivation system. Owners note that during calm driving on an open highway, the improvement according to the on-board computer amounts to 5–8 percent.
However, in urban conditions or during active acceleration, the advantage almost disappears: the system rarely has time to switch into an economical mode. Reviews from Chevrolet Tahoe and Cadillac Escalade owners show that in mixed driving, the difference is often limited to 0.5–1 liter per 100 km. The owner of a 2016 Tahoe, after disabling AFM, noted virtually unchanged consumption along with smoother engine operation. Similar observations are found among Ram 1500 owners with MDS: some record a gain of 1–2 MPG on the highway, while others do not notice any tangible changes after disabling the system.
A comparison of identical vehicles with the function activated and deactivated shows that the technology does produce an effect, but within a limited range of conditions — mainly during steady highway use.
Advantages and Risks
From an environmental standpoint, the solution allows manufacturers to comply with strict regulations without switching to hybrid powertrains. Reducing the number of active cylinders lowers CO2 and NOx emissions under low load. At the same time, the upgrade does not require a complete redesign of the engine: special lifters and the appropriate software are sufficient.
Nevertheless, questions about durability remain. The story of the Cadillac V8-6-4 became illustrative. And modern AFM and DFM versions on General Motors 5.3- and 6.2-liter engines are often accompanied by complaints: lifter wear, increased oil consumption, and camshaft lobe damage. Silverado and Tahoe owners report the need to replace parts as early as 50,000–80,000 kilometers and often switch to standard lifters with an ECU reflash.
At Chrysler, the MDS system can also cause vibrations and a sense of uneven operation. In Honda Odyssey and Honda Pilot models with VCM, despite active mounts and noise cancellation, some owners prefer to disable the function. Volkswagen's ACT on the 1.4 TSI is generally characterized by smoothness, although during prolonged driving on two cylinders, some note slight vibration.
The conclusion looks mixed. Under calm driving and primarily highway use, the system is capable of delivering noticeable, albeit moderate, savings. In a megacity or with a dynamic driving style, the benefit is reduced to a minimum, while the likelihood of expensive repairs remains. Therefore, before buying such a car, it is wise to assess your own usage pattern: a few percent in savings may not compensate for possible technical nuances.