Alfred T. Palmer on Wikimedia

An engine is a sealed box where controlled explosions happen a few thousand times every minute, and the whole arrangement depends on parts that can flex without leaking. Pull the cover off any motor and you find rubber doing most of the unglamorous work. There are seals around the crankshaft and gaskets under the valve cover, plus every hose carrying coolant and every belt turning an accessory off the front pulley.

None of it would survive a week under a hood without a process that a bankrupt American stumbled into in 1839. He dropped a mixture of rubber and sulfur onto a wood stove and watched it char instead of melt. He spent the next two decades in and out of debt, and he died owing money to a long list of people.

Rubber That Didn't Work

Natural rubber was a commercial disaster before 1839. The material went soft and sticky above room temperature and turned brittle in the cold, which meant goods sold in April came back through the door in July as puddles. An American rubber boom in the 1830s collapsed for exactly that reason, taking a string of companies and their investors down with it.

Charles Goodyear had bought into that boom early and refused to let go of it afterward. He mixed rubber with anything he could get hold of, including magnesia and nitric acid, and he kept experimenting through repeated stints in debtors' prison. The pattern held long enough that his family lived on borrowed money for most of a decade.

The break came in Woburn, Massachusetts, when a batch of rubber mixed with sulfur either fell or got placed onto a hot stove, and instead of running into a sticky mess it charred like leather. Goodyear noticed that the rim of the scorched piece had stayed springy, which was the one property nobody in the trade had managed to produce on purpose.

What the Sulfur Does

Vulcanization works by building sulfur bridges between the long molecules in rubber. Untreated rubber is a tangle of long chains that slide past each other when warm. Lock those chains together at intervals and the material stretches under load, then pulls itself back into shape when the load comes off.

The useful consequence is a vulcanized compound stays elastic across a span that runs from a freezing morning to the inside of a hot engine bay, which is precisely the window a car has to work in. Nothing else available in the nineteenth century came anywhere close to that. The name came from Vulcan, the Roman god of fire, and it was suggested by one of Hancock's associates rather than by either inventor.

Goodyear received US patent 3633 on June 15, 1844. Thomas Hancock had already filed in Britain the year before, having worked backward from samples of Goodyear's material, so the British patent came first. Goodyear was celebrated at international expositions through the 1850s and was barely solvent when he died in 1860.

Where It Shows Up Under the Hood

A contemporary four-cylinder carries dozens of separate rubber parts, nearly all of them invisible until one of them fails. The valve cover gasket keeps oil off the exhaust manifold, and the O-rings at every fitting hold coolant and fuel inside their lines. One perished seal the size of a coin will put an entire oil pan on a driveway overnight, and the repair bill rarely matches the part.

The hardest work goes to the parts that never stop moving. A serpentine belt bends around its pulleys something like a hundred million times before a mechanic gets to it, and coolant hoses flex through heat cycles for a decade or more. Nitrile and silicone compounds replaced natural rubber in those jobs generations ago, and both are cross-linked by the same reaction Goodyear found on his stove.

Mounts hold the engine in the car and swallow the vibration it makes, with newer designs sealing fluid inside a rubber body to damp the worst of it. Service schedules reflect the whole arrangement, since the parts a garage replaces most often are rubber rather than metal. Goodyear himself never saw an internal combustion engine. He died a quarter century before anybody built one that ran.