Spotlight
Four decades of wax, oil and road grime — and the question of how to remove it without removing cables, seals and stickers along with it. A morning with dry ice in Berlin-Buch, using our E30 325iX Touring as the example.
Why an E30 engine bay looks the way it looks
BMW generously preserved the E30 at the factory. Cavities, panel seams and large parts of the engine bay received a layer of wax that kept rust at bay for decades — the reason why many E30s are still on the road today with original inner fenders. The drawback only shows over time: wax stays soft, absorbs dust, oil mist and brake dust, and turns into a grey-brown, sticky layer that can no longer be removed with a rag and cleaner. On top of that comes the insulation mat on the underside of the bonnet, whose foam disintegrates and crumbles after so many years.
The classic methods all have a catch. A steam cleaner only loosens the wax on the surface and forces water into connectors that were not built for high pressure in 1988. Solvents attack plastics and lettering. Sandblasting is off the table in the engine bay anyway — the grains stay everywhere.
What dry ice blasting does differently
In dry ice blasting, pellets of solid carbon dioxide at around minus 78 degrees Celsius are accelerated onto the surface with compressed air. Three things happen at once: the impact mechanically loosens the dirt, the cold makes the dirt layer brittle so it flakes off the surface, and the dry ice goes directly from solid to gaseous state the moment it hits — it sublimates. The gas volume is many times the pellet volume and effectively blasts the dirt away.
The decisive difference from all other blasting methods: nothing is left behind. No sand, no water, no solvent. What lies on the floor after blasting is the dislodged dirt itself. The blasting medium has disappeared.
For an engine bay, that means: electrics, connectors, ignition system and carburettor or fuel injection stay dry. Nothing that is afraid of water needs to be taped off, and the engine can be started immediately after cleaning.
The example: 325iX Touring, an hour and a half
Our Touring stood in the workshop matching the description above: factory wax in every corner, overlaid by 38 years of use, plus the disintegrating bonnet insulation. The task was clearly defined — remove most of the wax, remove the insulation mat completely, and damage nothing that is original in the process.
The most important parameter is not the machine but the pressure. Dry ice can be blasted at very different intensities, and a classic car demands the lower half of the scale. Old PVC cable insulation becomes hard and brittle over the years; at full pressure it cracks open. The same applies to vacuum hoses, rubber grommets and the lettering on expansion tanks and fuse boxes. Anyone working with industrial settings here leaves behind a clean engine bay, but also a damaged one.
Accordingly, work was done section by section: reduced pressure on the wiring harness, lines and connectors, more force on sheet metal, engine block and mounting brackets, where the wax sat thickest. The insulation mat on the bonnet came off in strips — the foam disintegrates under the cold, the adhesive becomes brittle and can be removed without attacking the paint on the underside of the bonnet.
After an hour and a half, the engine bay was in a state otherwise only seen in restorations with the engine removed. The wax layer is mostly gone, the metal shows the factory colour again, cast parts and aluminium are exposed. Deliberately left untouched were spots where the wax still does its job — in the seams and cavities it stays, because no one looks there and it continues to prevent rust.
What the process can do — and what it can’t
- Dry: no water in electrics and connectors, no drying, no starting problems afterwards
- Residue-free: no blasting medium left in ventilation ducts, threads or bearings
- Gentle with the right settings: paint, plastic, aluminium and rubber remain unharmed if the pressure is right
- No disassembly: engine, wiring harness and ancillary units stay where they are
- Thorough: wax, oil, grease and dirt also come out of corners that neither brush nor rag can reach
- Without chemicals: carbon dioxide, which occurs as a by-product anyway — no solvents, no wastewater
The limits are equally clear. Dry ice does not remove rust; anyone who finds a spot of rust needs a grinding or blasting treatment with solid blasting medium afterwards, plus a sealant. Paint that is already flaking is loosened further by the cold — that is correct in itself, but can come as a surprise. And the wax is gone after cleaning: anyone who does not re-protect the engine bay afterwards trades protection for looks. For the exposed metal surfaces, a transparent corrosion protection is recommended so that the factory colour remains visible.
Dry ice also works well underneath the car. Engine and gearbox housings, suspension parts and the underbody can be freed from oil and old underbody protection in the same way — there with considerably more pressure, since there is no sensitive electrics to worry about. For an assessment before a purchase or before a restoration, this is often the fastest way to see what is really going on underneath the layer.
Where we were
The work was carried out at Blackwood Solutions in Berlin-Buch, a company founded in 2022 that specialises in dry ice blasting and other blasting methods. No one there needed to be told that the settings for an old wiring harness are different from those for an industrial plant — experience with classic cars was the reason why the Touring ended up there. Anyone planning a comparable project, whether engine bay, underbody or drivetrain unit, will find a contact there who knows the vehicles in question. This is not an advertisement but a recommendation based on our own experience.
Conclusion
Dry ice is not magic but physics: cold, impact and sublimation dissolve what has accumulated over decades, without leaving behind water or chemicals. The difference between a good and a bad result lies not in the equipment but in the hand that sets the pressure. An hour and a half gave our Touring an engine bay that we would not have achieved with a rag and cleaner in weeks.
From dirty to clean: the whole session in pictures
