How Much Rust Is Too Much On A Car?

How Much Rust Is Too Much On A Car
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    Does the family mini-van or cruiser have a brown, rusty spot developing? Your concern is understandable. A spot of rust is common on vehicles. However, there is such a thing as too much rust on the family car.

    Generally speaking, surface rust and scale rust are minor problems that present themselves on the vehicle’s metal “surface”; they require eventual repair but are not an emergency. However, penetrating rust, which punctures holes in the car, and any rust on the undercarriage, are extremely dangerous, and a mechanic should investigate the problem immediately.

    Keep in mind that there is technically no hard and fast percentage or measurement for what “too much rust” is. Only a mechanic can make that exact distinction. But you can estimate if rust warrants immediate repairs and urgent attention by assessing the location and severity of rust development before taking the car into the shop for repairs. 

    Keep reading for more information on gauging the rust levels of a vehicle and more about fixing a rusty situation.

    Too Much Rust Is When Door Crumbles

    What Is It Rust?

    Before exploring what “too much rust” looks like, we need to understand what exactly rust is. Rust is the everyday term for the process of creating iron oxide.

    Without getting too deep into the science of chemical conversions, “rust” results from a chemical reaction between iron and water. A “rusting” vehicle is technically experiencing the oxidation of iron. You can think of rust as the process and byproduct of rotting iron. 

    How Does Rust Develop?

    Rust occurs naturally in metals containing iron. Only products made of iron or its alloys, like steel, will rust. In terms of development, rust forms when iron, hydrogen, and oxygen mix.

    Iron and steel only rust when exposed to moisture. Rust is prevalent in areas with high humidity. In a perfectly dry environment, rust would not exist. Unfortunately for cars and trucks, water exists in most places, meaning that vehicles are prone to rust just about anywhere.

    It’s important to note that salt or magnesium chloride can erode a vehicle experiencing rust faster. Vehicles exposed to ocean salt-spray or salt-heavy air are more prone to rusting. Additionally, winter months put cars at risk for rust because of the use of magnesium chloride to melt ice and snow on the roads.

    When Should I Worry About Rust? Is Rust Dangerous?

    The presence of rust is dangerous to both the car and your family. Thus, whenever rust appears on a vehicle, some immediate concern is warranted.

    Rust leads to vehicles losing their integrity and causes them to be unsafe to drive eventually. Additionally, rust creates an uneven, jagged surface on cars that children and adults may accidentally cut themselves on. 

    A Note On Tetanus

    It’s a common misconception that a wound from rusty metal causes tetanus. Rust does not cause tetanus; it is a bacteria that often lives on rusty objects that causes tetanus. 

    How To Know If A Car IS “Too Rusty?”

    When it comes to rust, deciding when it needs addressing from a professional can be difficult. In some respects, rust seems harmless, nothing more than an eyesore on the family hatchback.

    But, you can generally find out if rust needs immediate attention by inspecting the areas of a car most prone to rusting and diagnosing the stage of the rust. The combination of rust stage and location will determine the severity of the situation. 

    How Much Rust Is Too Much On A Car? 1

    Stages of Rust & Their Severity

    Rust damage occurs in three stages—the later the stage of rust, the more expensive and dangerous the situation.

    Stage 1: Surface Rust

    Most mechanics consider surface rust as any rust that impacts only the top layer of a car’s body panels—most surface rust forms due to nicks or dings in a vehicle’s paint. Seemingly minor damages like a fender bender or hail can cause extensive surface rust development. 

    In terms of urgency, the risks of surface rust to a vehicle or its occupants are relatively low. Surface rust is more a cosmetic detriment than anything. However, it should not be left alone for long. Ignoring surface rust allows it to develop into a deeper, more expensive, and far more dangerous vehicle and family situation. 

    Is Surface Rust Fixable?

    Yes, surface rust is fixable. Most DIYers can manage the repairs themselves. With some sanding and elbow grease, surface rust easily removes from a car. Provided the damaged area is painted and sealed correctly, the rust should stop developing. 

    Repair Urgency: Low

    Stage 2: Scale Rust 

    Scale rust bridges the gap between extreme rust damage and easily repaired cosmetic rust. When surface rust is left untreated, it continues to grow until it pits the metal, becoming scale rust. 

    Scale rust is a more severe situation than surface rust. When scale rust develops, the integrity of the car’s metal starts to fail. The vehicle is weakened against impact and becomes less durable, making it less safe to drive and prone to more damage in an accident. 

    Is Scale Rust Fixable?

    Yes, when caught in time, scale rust is fixable with a similar process to surface rust. However, the sanding and removal of rust tend to take longer with scale rust. Usually, professional sanding equipment and expertise need calling in to address scale rust, or you risk damaging the vehicle’s panels. 

    Repair Urgency: Moderate

    Stage 3: Penetrating Rust

    The most severe level of rust damage is penetrating rust – this is the rust that every junker car in America seems to have. The name is pretty self-explanatory: penetrating rust breaks through the car’s metal, puncturing holes through the steel. 

    Penetrating rust tears a car to pieces. As it worsens, the vehicle’s structural integrity weakens, and eventually, entire parts of a car can fall off. 

    Is Penetrating Rust Fixable?

    Penetrating rust cannot be sanded off by a handy DIYer. Once rust punctures holes into metal, that part of the car needs removing and replaced. A professional auto-body mechanic will need to handle the repairs.

    Repair Urgency: High

    How Much Rust Is Too Much On A Car? 2

    Common Locations of Rust & Their Severity

    The body panels of the car are essentially just the top portion of the vehicle. Common areas for rust to develop on body panels include the corners of the car doors, the wheel wells, and the vehicle’s bumper.

    Body Panels 

    Most body panel rust does not require immediate attention unless it has gone beyond a surface level, but you should never ignore it. Address body panel rust quickly to prevent the need for an entire panel replacement. 

    Is Body Panel Rust Fixable?

    Most of the time, body panels are repairable through sanding and repainting. However, if body panels have experienced penetration from rust, they usually need replacement.

    Repair Urgency: Moderate

    Undercarriage or Frame Rust

    Finding frame rust requires some gymnastics on your end, or at least an automotive jack. In general, a mechanic must immediately address rust on the frame or undercarriage of a vehicle.

    Frame damage from rust can cause the dislocating of a vehicle’s suspension or steering wheel or cause the car’s cabin to fail to protect occupants during an accident. 

    Is Undercarriage Rust Fixable?

    If caught early, well before penetration, frame rust usually is repairable. However, extensive frame damage puts the car at risk of literally falling apart. Severe frame rust can result in a vehicle being unsafe to drive, to the extent that a police officer in some states can have the car towed for being unsafe.

    Repair Urgency: High

    How Fast Does Rust Spread?

    Rust does not spread like a bacterial infection. It only grows when metal constantly experiences moisture exposure. Severe rust damage takes several months to years to develop, but surface rust develops in a matter of hours.

    So, in wet environments of the coastal U.S.A. or humid states like Minnesota, rust develops faster on exposed metal. Additionally, rust grows faster if corrosive chemicals mix into the moisture, like salt or magnesium chloride. In general, a spot of rust develops immediately after exposure to water and continues to grow under moist conditions until there is no more metal for it to consume. 

    Can You Fix Rust Yourself? 

    Yes, sometimes, a car owner can tackle rust on their own. No spray or treatment removes rust. The only solution is sanding off the rust and repainting the car or removing damaged parts and repainting in severe cases.

    Whether you can sand and repaint the vehicle yourself depends solely on the extent of the rust damage. If the rust has punctured any part of the vehicle with visible holes or has eroded and warped the undercarriage, do not treat the rust yourself – take it to a professional.

    Can You Prevent Rust?

    Yes, rust is preventable! Preventing rust doesn’t take a lot of work. You can use some of these methods to protect your family vehicle from rust damage:


    Rustproofing generally utilizes some form of dripless oil or tar spray on the undercarriage of a vehicle. The spray hardens into a shield, protecting the car from moisture and rust. Usually, a mechanic needs to perform the rustproofing for you, as they have the equipment to lift the vehicle for access to the undercarriage.


    It may seem counterintuitive, but washing the car does help prevent rust. Regular car washing prevents the build-up of corrosive materials on the undercarriage that contribute to rust development.

    Carwashing is especially essential in areas that use magnesium chloride on roads during the winter. Unless you wash magnesium chloride off, it will continually eat away at the metal of a car’s body. 


    Surprisingly enough, immediately cleaning and repainting any nicks or dings on a car will help prevent rust. Rust only develops if the car’s surface remains exposed to moisture. Repainting will seal the metal, protecting it from moisture exposure. 

    Car Waxing

    Waxing the car does more than enhance a vehicle’s paint job. It provides an extra layer of protection for the vehicle’s paint, reducing the chance of rust developing on the body. 

    A Final Word On Rust and Cars

    When it comes to rust, the wisest course of action is immediate action. The longer you allow rust to grow, the more expensive and difficult it is to fix, and the more dangerous a vehicle with rust becomes. Whenever you have concerns about rust, contact a local autobody shop or mechanic to investigate. 

    While you’re working to keep rust at bay, don’t forget to address other important car care concerns, such as cleaning urine out of car seats, understanding how far to drive on a spare tire, and knowing the cost of heated seat repairs.

    Avatar of Keren Simanova

    Keren Simanova

    Welcome to my car seat blog! As a mom of 3, I put together with other hard-working moms a highly informative one-stop car seat resource, full with many reviews and buyer guides. I hope you find it invaluable. Thank you for trusting me & my team! - Keren
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    Keren Simanova

    Welcome to my car seat blog! As a mom of 3, I put together with other hard-working moms a highly informative one-stop car seat resource, full with many reviews and buyer guides. I hope you find it invaluable. Thank you for trusting me & my team! - Keren