How much rust is too much on a car?

Last updated January 20, 2023

Rust is a common problem among car owners that can vary in severity. Over time, rust can cause extensive and costly damage to your vehicle if it is not dealt with in a timely manner. If you have failed to proactively tackle rust, you may find that when the time comes to sell your car, the car valuation is reduced due to its poor condition.

Therefore, knowing exactly how much rust is too much is key when it comes to maintaining the overall condition (and value) of your car. In this guide, we will explore the impact rust can have on a car – and highlight what qualifies as 'too much' rust, so you can make informed decisions when it comes to maintenance and repair.

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How do you know if your car has too much rust?

The first way to tell if your car has too much rust is to inspect its bodywork for discolouration and flaking paint. If there are any rusty spots, these should be checked further as they could indicate more serious corrosion below the surface that requires urgent attention from a professional mechanic.

Another indication of excessive rusting is certain parts becoming loose or rattling when driving over bumps. This could indicate that the metal underneath them has become weak due to corrosion, which could cause more serious issues in the long run.

What is considered ‘bad’ rust on a car?

When assessing the severity of rust on your car, it's important to consider how much damage has already been done and how quickly it may be spreading. Anything more than surface rust or light pitting is considered 'bad' rust and should be assessed by a professional mechanic immediately.

Bad rust can quickly spread from small areas into larger ones, leading to compromised structural integrity and further corrosion issues over time. In some cases, bad rust may require bodywork repairs or even replacement parts in order to restore the vehicle back to its original condition.

How much rust is acceptable on a car?

When looking to sell your car, any amount of rust could put off potential buyers. If you want to sell your car privately in the future, it’s worth ensuring that you keep rust at bay to avoid decreasing the value of your vehicle or deterring potential new owners.

What causes rust on cars?

The main cause of rust on cars is exposure to moisture. When water comes into contact with metal surfaces, such as car bodies, oxidation begins and leads to rusting. This process tends to be accelerated when the water contains salt or other minerals due to the environment where the car is kept or driven (e.g. near the sea).

Corrosion may also occur due to exposure to road chemicals such as the de-icing salts used during wintertime.

Stages of rust

Rust development on cars occurs in the following stages, becoming progressively worse over time:

  • Oxidisation occurs as oxygen molecules react with iron molecules, which creates an oxide layer to protect the metal surface from further damage. The beginnings of rust may be invisible to the naked eye at this stage.
  • Water comes into contact with this oxide layer (the ‘mill scale’), causing it to erode away over time. Iron molecules are exposed, leading to the formation of visible rust.
  • With further exposure to the elements, this layer is eroded even more, causing paint to flake and weakening the metal surface until it becomes damaged.

Rust locations and what they mean

  • Around the wheels

    Rust formations around your wheels are generally due to contact with the elements. The bottom of your car’s body, around the wheels is the area that’s most susceptible to rust formation, as it regularly comes into contact with water, snow and other moisture.

  • Around the bumpers

    Your car’s bumpers may begin to rust after some time, again due to their exposure to the elements and age-related wear and tear.

  • Around the doors

    Although car doors aren’t exposed to the elements as forcefully as wheels and bumpers, the consistent movement of the doors over time could lead to rust developing and worsening faster.

How to prevent your car’s frame from rusting

You should make sure that you are regularly washing your vehicle with soap and water, paying special attention to any exposed areas such as the undercarriage or wheel wells. Removing dirt, road salts, chemicals, and other contaminants can drastically reduce the risk of corrosion.

It’s also important that you wax your car regularly, as this provides an extra protective barrier between the metal surface and the elements.

How long does a rusted frame last?

Once rust takes hold, it will continue to get worse. When it comes to the life expectancy of a rusted car frame, there is no simple answer. The amount of rust on the frame, as well as how it was used and maintained before becoming rusty, can heavily influence its lifespan.

Generally, however, a rusted frame will last anywhere from 5-15 years depending on the severity of the damage.

Can you paint over rust?

Rust should be removed from any areas where it has started to eat away at the metal before any paint is applied. If not properly removed beforehand, rust will spread underneath the paint before it eventually ruins your work.

If you want to achieve a good quality finish, lightly sanding down any rusted areas will help to create an even surface for priming and painting.

Does rust spread from contact?

Rust does not generally spread from direct contact with other rusty objects or surfaces. Instead, the primary way in which rust propagates is through moisture. When humid air comes into contact with iron or steel, the metal quickly begins to corrode and form rust spots.

This process can be accelerated if salty water or other corrosive substances are also present. Therefore, even if two rusty objects come into indirect contact, such as through rainwater runoff, they can still become even more rusted over time if left unchecked.

Is rust worth fixing on a car?

If you’re thinking about repairing rust on your car, your first consideration should be whether the repairs are financially viable.

Depending on the severity of the rust on your car’s bodywork, it can work out more expensive to repair the damage than to simply replace the affected parts. Of course, the best and most cost-efficient way to avoid rust damaging your vehicle is take measures to prevent it developing in the first place.