Mercedes' F1 electric turbo in a 1.5 is clever, but reliability will decide

Is the combustion engine finished, or just being quietly rebuilt while everyone looks at batteries? Mercedes' latest answer is a 1.5-liter gasoline four-cylinder with an electric turbocharger, and it suggests the second option.

What Mercedes actually announced

The engine is called the M 252 LS, and it debuts in the GLB 250. According to Autonext, it replaces the 2.0-liter M 260 at the top of the GLB range. It makes 231 hp, uses a 48-volt electric turbocharger and two balance shafts, and Mercedes claims 17 percent less CO2. The turbo is derived from Formula 1 technology.

One caveat on the headline number. Motor1 quotes 228 hp, while Autonext and Motor.es say 231 hp. Automotive World lists the output in kilowatts (170 kW). The gap is probably a matter of units, but treat the exact figure with care. Autoblog says the GLB 250 could potentially be sold stateside, though that's not confirmed.

The smart part is replacing a bigger engine, not adding power

The tempting reading is "F1 tech, so more horsepower." We think that's the wrong lens. The interesting claim is that a 1.5 now sits at the top of a range that used to be served by a 2.0. Smaller displacement usually means lower friction and lower fuel use, but it has historically cost you in response and in the way the engine feels when you ask for power. An electrically driven turbo attacks exactly that weak spot, because it doesn't have to wait for exhaust flow to build up.

If it works as advertised, this is a better use of F1 know-how than the usual halo-car marketing. It's a technology moving into the car that most people actually buy, and that's the only kind of racing transfer that matters. The 17 percent CO2 cut is a manufacturer's claim, and we'd read it as the upper end of what the company wants to show, not a promise for every driver.

The test isn't the spec sheet: it's year eight of ownership

Here's our skepticism. Every added component is something that can fail. A 48-volt system, an electric motor in the turbocharger, and the power electronics around it all have to survive heat, vibration and years of stop-and-go traffic. Racing gets away with intense service schedules. A family crossover doesn't.

The earlier M 260/M 264 family already paired its turbo with an integrated starter-alternator that, per Automotive Tech Info, can add 15 kW (20 hp) briefly. Mercedes is clearly comfortable stacking electrification on small engines. But comfort in a lab is not the same as proof on the road, and we haven't seen durability data or independent consumption figures. Until those arrive, the CO2 number is a promise, not a result.

Real-world efficiency is the second trap. Official cycles reward clever boost control. Highway cruising at speed, cold starts and short urban trips are where small turbo engines often give back their savings. We'd wait for independent fuel economy testing before crediting the 17 percent.

Why this matters even if you want an EV

Spending development money on a new gasoline four-cylinder tells you, in our view, what Mercedes thinks about the next several years: hybrids and efficient gasoline engines stay in the mix, and they need to be cleaner to stay there. That's our reading, not something the company has put in those words.

Our verdict: this is worth watching and worth applauding, and not worth buying on faith. If you're shopping in this segment, wait for real-world mpg figures and the first reliability reports before paying for the novelty. If those look good, the e-turbo could become the quiet standard for small gasoline engines. If they don't, it'll be remembered as a very expensive way to say "F1" on a brochure.