One of the recurring questions in the Power-to-X debate is what happens to the hundreds of millions of combustion vehicles already on the road once renewable synthetic fuels (synfuels) become available. A scientifically grounded Swiss study has now delivered a clear answer for one important segment: classic cars.

A year-long test programme on Swiss roads

Over more than twelve months, Empa, the federal interdisciplinary research institute of the ETH Domain, worked together with AMAG Classic and lubricant specialist Motorex to investigate how synthetic gasoline behaves in vintage engines. Two reference vehicles were used: a 1978 VW Golf I with a 1.5-litre four-cylinder engine and a 1971 Chrysler Valiant with a 3.7-litre six-cylinder. A bio-synthetic 98-octane gasoline made from renewable methanol was compared against a conventional fossil 98-octane reference fuel.

The test programme combined three layers of investigation: direct material exposure of components between tank and engine, emissions and consumption measurements on a chassis dynamometer, and real-world driving over thousands of kilometres – including Alpine routes such as the Flüela Pass in the Engadin.

Key findings: no material damage, no performance loss

The results are unambiguous. Across seals, carburettors, fuel hoses, plastic components such as carburettor floats and fuel filters, tank sensors and the sheet-steel tank itself, no physical, haptic or visual changes were detected after exposure to the synthetic fuel. No corrosion appeared on the inside of the fuel tank.

On the emissions side, three consecutive WLTP measurements per fuel were performed on a more modern but emissions-stable VW Jetta. The regulated exhaust emissions were indistinguishable between bio-synthetic and fossil gasoline. Particulate emissions showed a slight trend toward lower values with synfuel during simulated motorway driving. Volumetric and energetic fuel consumption showed no measurable difference.

Wheel power measurements with the VW Golf on Empa’s single-axis dynamometer confirmed near-identical static and dynamic performance with both fuels. Over 3,369 kilometres with the Golf and 2,862 kilometres with the Valiant – a mix of motorway driving, short trips of 500 metres to 15 kilometres, and extended standstill periods typical for classic cars – the AMAG Classic drivers reported no perceptible differences except for a slightly altered exhaust smell that was not described as disturbing.

An honest caveat: the engine oil surprise

The study did encounter one finding worth flagging. Engine oil analysis showed unusually high iron and lead levels in the Chrysler Valiant – higher than expected. Empa and AMAG Classic followed up with additional tests using a comparison vehicle running on conventional gasoline. The conclusion: a direct causal link to the synthetic fuel could be ruled out.

Christian Bach, head of Empa’s Vehicle Drive Systems Laboratory, offered a plausible explanation: bio-synthetic gasoline has a slightly higher solvency than fossil gasoline due to its molecular structure. This solvency can dissolve deposits that accumulate over decades of operation on leaded fuel. In other words, the elevated metal readings reflected the history of the engine, not damage from the new fuel.

Why this matters beyond the classic car community

Empa estimates that around two million combustion-engine vehicles will still be on Swiss roads in 2040. Globally, the existing fleet of internal combustion passenger cars exceeds 1.3 billion units. None of these vehicles can be retroactively converted to battery-electric drive at meaningful scale. If the existing fleet can be operated on CO2-neutral fuels even partially, the climate impact is significant.

The Swiss study confirms what theory suggested but had not been rigorously verified for older engines: drop-in synthetic gasoline works. AMAG Classic has since taken delivery of solar gasoline from Synhelion for its own classics. Synhelion’s industrial demonstration plant DAWN in Jülich, Germany, has been operating since late summer 2024 and is producing renewable jet fuel, diesel and gasoline, with a commercial-scale plant in Spain in development.

SPIN Perspective

This study illustrates a Power-to-X principle that is sometimes lost in the polarised debate around mobility transition: defossilisation is not a single-technology contest. Battery-electric drivetrains will dominate new passenger car sales – but they cannot defossilize the installed base of combustion vehicles, nor sectors such as aviation, shipping or heavy duty applications where liquid hydrocarbon energy density is structurally needed.

Synthetic fuels are not a competitor to electrification; they are a complement that targets molecules where electrons cannot reach. The Empa–AMAG Classic study removes one technical objection from that conversation. The remaining barriers are now squarely economic and regulatory: production cost, scaling pace, and the policy frameworks that determine whether renewable molecules can compete with subsidised fossil fuels. These are precisely the questions Switzerland’s Power-to-X community is working to answer.

Sources: Empa, AMAG Medienportal, Synhelion.