Brown rust bubbles at the bottom of doors, scratches and minor dents that have turned brown and ominous stains around the wheelarches...
All these are tell-tale signs that oxidation, the term used to describe the chemical breakdown of metal, has started. If left unattended, rust can eat holes in the bodywork within the space of a few years.
Rust preys on all iron-based metals but it can be kept at bay. The best tip is to be vigilant, say experts.
"Owners who take a regular look at some of the nether and darker regions of their cars and who pay attention to them can avoid rust," says Marius Brune. He runs the Classic Data database, which keeps track of the prices being paid for cherished cars.
"A lot of people just clean their cars on the surface, buffing up the chrome and paint to give them a sheen," says Brune. "It's more important to look underneath and make sure the car is clean there too."
The important areas to watch are the underside of the car and the inside rim of the wheelarches where mud and grime often collect.
"Older cars are not fitted with protective inner wheel arches, with the result that dirt thrown up from the road by the tyres finds its way into all the nooks and crannies such as headlamp recesses," says Brune.
A high-pressure water jet can be used to flush out these rust traps, a job which should be carried out at least once a year.
Goetz Knopp, who heads a classic car club based in Germany, recommends giving older cars the complete anti-rust treatment.
"Rust can be converted using a chemical treatment or else sandblasted to reveal the sound metal underneath, provided the holes are not too large," said Knopp.
A rust converter will turn iron oxide into a more stable form such as iron tannate and most leave behind a black sheen. Before application the surface must be cleaned to remove loose rust and soiling. A wire brush can be used for the work.
If all else fails the rusted sections must be mechanically cut out and new metal welded in. This is a job best left to professionals.
Frank Meyer, who works for the German Autobild Klassik magazine which caters for the owners of cherished cars, has another tip: Check the window surround and sunroof rubbers. These become porous over time and water finds its way into unseen bodywork crevices. If not spotted in time rust here can spread and cause significant - and expensive - damage.
An even more thorough look can be gained by using an endoscope or a powerful LED lamp narrow enough to be able to throw light into the hollow parts of panels.
"Hollow panels have small drainage holes so that the water and condensation can escape. If the holes are blocked with dirt this cannot happen," says Meyer, who recommends using thin wire to poke free the blocked holes.
To get a really good look at the underside of a car, the surfaces must be free of contaminants such as dirt, oil and grease. Various methods are available to do this, including a dry ice treatment which leeches off the dirt leaving a finish similar to that obtained by sand-blasting.
Both methods are best left to experts who know which areas to treat and which to leave well alone. For a less abrasive clean a blasting of fine plastic beads will remove surface residue without causing collateral damage.
If a cherished vehicle is used as a second or fun-day car there is no better way to protect it than by restricting its use in harsh, wet climates.
The salt used to dissolve ice and snow on roads in countries with snowy winters is highly corrosive. It will attack any unprotected metal surface and continue to take its toll even when the car is parked in a ventilated garage.
Experts advise owners to regularly take the car through a car wash that has an under-spray function. This will reduce the chances that salt and salt water adhere to the vehicle and start to corrode. — dpa
