Corrosion in Cars

NEW CARS

When buying a new car, you may consider having it ‘rust-proofed’. If you decide to have it done, ensure the personal is a reliable professional whose materials and workmanship comply with Australian Standard AS2662, and who will issue at least a 5 year guarantee.

 There is some doubt as to the value of rustproofing. It is very difficult to get the protective waxes into some of the parts of the car body. If you cannot be sure that this will be properly carried out, then it may be better to avoid this expensive process.

Only new cars should be rust-proofed as treating a car that has been on the road for a period may be worse than no treatment at all.

BODYWORK

The main cause of car body corrosion is the accumulation of dirt. When the dirt becomes damp and stays damp, it allows corrosion to begin – long after the rest of the car is dry. Washing just the outside of your car will not stop it corroding. You must hose off the caked-on mud on the wheel arches, the sills and underneath the car. This is especially important after visiting the beach or driving on dirt roads in the outback. In many overseas countries, salt is put on the roads in winter to keep them free from ice. Under these conditions the salt, combined with damp mud, provides a lethal combination of grime which is able to bite through metal in no time at all.Wash the paintwork with a soft brush and solution of water and special car detergent (do not use household detergent as it may promote rust!). Remove bugs and road tar with tar remover or methylated spirits. Rinse the car after using any special cleaners.

All car doors have drain holes in the bottom. These should be regularly checked to ensure water cannot be trapped inside the door cavity. Should your floor mats get wet, take them out and dry them. Trace where the moisture is coming from and stop any leaks.

Putting a wet car in a warm closed garage accelerates corrosion as the water will not immediately evaporate and condensation may occur on the cold car body. If your car is wet, leave the garage door open until it dries. In many respects, a large carport is better than a garage; it keeps the rain off and allows circulation for the car to dry. However, if you only use your car occasionally, or have a carport which doesn’t protect from rain, dew and pollution such as soot or salt, a garage is a much better option.

CHIPPED OR SCRATCHED PAINTWORK

If the paintwork on your car becomes chipped or scratched, repair it as soon as possible. Minor paint damage can be easily repaired as long as it is carried out correctly. Painting over rusted areas is worse than doing nothing.

Good surface preparation is the most important part of the touch-up process. Scrape away loose paint and rust and clean to bare metal using an electric drill and silicon carbide paper. ‘Feather’ the edges of the intact paint so there is a gradual change from the good painted region to the bare steel region. There must be no rust remaining on the bare steel. Wipe away the dust and apply a phosphoric acid metal conditioner. This will dissolve any traces of rust and etch the surface to provide good key for the paint. Apply a primer and top coat. For small scratches, an artist’s brush is best; larger areas will need a spray application. If using a spray can primer and top coat, make a mask from a piece of cardboard, cutting a small hole in the centre so that only the damaged area is exposed. Follow the instructions on the can regarding shaking, applying and cleaning off excess.

Large areas of rust will probably mean the metal has corroded all the way through. This problem is especially noticeable along the bottom of doors as lines of blisters. Such areas can be repaired as long as the strength of the car has not been affected. The rusted areas will have to be cut out and replaced with “filler”. Kits are available on the market for such jobs and instructions should be followed. However, for a large job it is probably best to seek a local panel beater or car sprayer. They will have the correct equipment and do a professional job.

CAR BATTERIES

Before working on the battery, turn the engine off and disconnect first the negative, then the positive terminals. Beware of explosive hydrogen gas from the battery and avoid spilling acid. Scrub the terminal posts and cable terminals inside and out with a wire brush or special tool available for such jobs. Refit the cable and tighten terminals securely. Coat the terminals with petroleum jelly (do not use grease) to prevent corrosion.

COOLING SYSTEM

Most modern cars with an iron engine block and aluminium cylinder head require an inhibitor in the cooling water to prevent corrosion. The inhibitor is not antifreeze, although combination inhibitor-antifreeze solutions are available. It is essential to use only the inhibitor recommended in the owner’s handbook and, as they may work on different principles, you must not mix inhibitors.

Provided that the water circulating system is functioning satisfactorily, it is better to leave it undisturbed than to regularly flush it out. If the system is dirty, drain it, fill and add a can of cooling system cleaner. Operate the car according to the instructions and thoroughly flush. In soft water areas, refill, but if the tap water is hard (e.g. Adelaide) use tank water and add the correct concentration of inhibitor. Whenever you need to add cooling water, ensure that the concentration of inhibitor is maintained.

BRAKES

Corrosion of brake pipes may cause leakages. Examine your braking system periodically, wash off any encrustation of dirt and apply a coating of grease. If there is a marked drop in the fluid level, there may be a leak. Badly affected metal pipes or cracked rubber pipes will have to be replaced.

 EXHAUST SYSTEM

When you have to replace the exhaust on your car, consider buying one of the stainless steel exhausts that are now available for many popular models. A stainless steel exhaust has a much longer life than a conventional exhaust, though it does cost more initially. Alternatively, use an aluminium-coated exhaust. These are much cheaper than stainless steel but do not last as long.

This leaflet is one of a series on household corrosion produced by the Australasian Corrosion Association. While all care is taken, we cannot be responsible for any damage caused when carrying out these instructions. ACA EDUCATIONAL GUIDE & TECHNICAL BULLETIN