Rust is a bit like the boogie man of the automotive world. It's also one of the few universally understood issues. No matter who you talk to, they most likely know what rust is and that it's not good.
The problem with rust in cars is that (more often than not) it attacks things that relate to the safety and integrity of the car. This is because these items are usually made out of steel for strength and rigidity. This includes parts like the body, frame, suspension, steering components and brakes (basically every part of the car).
However, rust doesn't normally attack things with a protective coating, which is why painted body panels are usually in fairly good shape until the car is quite old.
So how can you prevent rust from occurring?
One of the most common systems is a little box that sits under the bonnet and uses battery power to blink a little LED light on and off that signifies that your car is "protected". This is normally an add on that is installed by the dealership. We might be a little biased but, as far as we can tell this is basically salesman mumbo jumbo that doesn't make a difference (on the same level as Peter Brock's crystal fuel economy improver).
In our experience there are only 2 things that truly prevent rust in cars, cleanliness and a good underbody coating (such as fish oil).
While it sounds like a really old school way of preventing rust, these underbody coatings add a sacrificial protective layer over the top of anything steel that prevents oxygen, humidity and salt from getting anywhere near the metal.
Additionally, cleanliness is huge in preventing a car from rusting. 4WD's in particular are exposed to environments with a higher concentration of salt, sand and sunshine (i.e. the beach or the tracks) which makes them much more likely to rust away.
Investing in a high quality underbody pressure washer and cleaning the car thoroughly after each trip will make a huge difference in keeping your pride and joy on the road and rust free.
So what about for people that don't go 4WD'ing?
Well, in actual fact, most modern cars rarely rust in our local climate (Brisbane). While it is humid and hot here, there's a low presence of salt and there isn't nearly enough rust activity for most vehicle owners to actually be concerned.
On top of that, most new cars are factory dipped, which means they have a factory coating preventing rust from attacking at all. Rust doesn't normally attack vehicles that are made from alternate materials such as aluminium and plastic. This means for most modern cars, rust really isn't a problem at all.
If you wanted to do anything, we might recommend giving the underside of the car a coating of fish oil once every 1-2 years for a road car and once every 6-12 months for anyone going off-road. Otherwise, our best advice is you don't need to buy the "magic rust box" that the dealership sells, just keep your clean.
If you have any questions about this blog post, would like a second opinion from a mechanic or would like to find an honest mechanic in Brisbane, check out Kashy here.