What Does Rust Under The Hood Mean?

Rust under the hood is surefire proof that your vehicle has been exposed to large amounts of road salt, either continually or for a singular incident. In any event, substantial rust damage cannot be ignored because it will eventually eat through the metal. So, what does rust under the hood mean?

Rust under the hood means corrosion that occurs to car components under your bonnets. Car components under the hood that are prone to rust include engine, transmission, radiator, AC compression, brakes, battery, and windshield wiper fluid. Those parts are so important and should not experience rust.

While you cannot stop rust from happening there, you can do all it takes to prevent or prolong the time of rust formation with proper maintenance. So, you can read below to find out the kind of rust that can happen under the hood and the best way to prevent them from happening.

So What Is Rust?

Rust happens when iron and oxygen combine to what is known as iron oxide. This happens when iron, metals and steels are exposed to prolonged moisture and air.

What happens is that water and carbon dioxide in the atmosphere combine to create a harmful acid which starts to dissolve irons. While this happens, some water starts disintegrating into oxygen and hydrogen.

What Is Rust

The most common parts of the car which are prone to rust are the exposed parts and also car undercarriage due to road salt accumulation.

However, many car owners fail to look at the car under the hood, which houses important components. This place also suffers from rust because of water leakage, bad humidity and heat.

What Kind Of  Rust Happens Under The Hood?

There are many types of rust that occur to cars. Here are the ones that are common to under the hood car components:

What Kind Of Rust Happens Under The Hood

  • Surface Rust: This is an early state of rust which isn’t that harmful to car parts. You can find this rust in your windshield water tank and battery bolts. It isn’t coarse, and you can clean them off with a soap, sponge and mild scrubbing
  • Scale and Penetrating Rust: When surface rust is left unattended to, it develops into a deeper problem. These types of rust are referred to rust that has eaten into under the hood metals and leaves hole marks.

Areas affected with these rust types look rough and need a more professional method to remove.

What Causes Rust under the Hood?

There are several reasons why car components under the hood corrode. Here are some factors which contribute to this:

What Causes Rust under the Hood

Paint Damage

When any part of the car hood has its paint wearing off due to heat or damp, rust sets in. This is especially true of transmission and battery. When their coat starts to wear off, it leaves them open to oxidation.


Car parts, particularly those under the hood and undercarriage, are likely to experience rust when exposed to salt. Many states use road salt to clear snow during winter.

The remnants of this salt find a way to get to parts under the hood of your car. Salt being an electrolyte combines with car metal to start rust formation.


While the under the car hood parts are covered, there remains slight openings where water can seep into especially during the rainy season.

Water sipping into your car bonnets is dangerous because it accelerates rust faster than other elements.


Too much heat and low humidity can be a cause for rust to set in your car hood. Since a car usually experiences overheating due to shortness of water, this could affect your car’s resistance to rust.

How To Prevent Under The Hood Car Parts From Rust?

There are several ways to stop your car parts from getting rust quickly, they are :

How To Prevent Under The Hood Car Parts From Rust

Washing and Waxing under the hood parts

The common way to prevent key car components from rust is by washing and waxing your car regularly.

The parts under the hood accumulate some dents from salt and bird droplets which can quicken the rusting process if not attended to fast.

When you wash these parts (steaming is recommended) it will remove and dangerous elements pass through under your car to the car parts.

When you take your car to the car wash, tell them to give it an underbody spray (comes with extra cash) which will remove dents and salt in areas like wheel walls and suspension car parts. These places are breeding locations for corrosion.

Clean all drain holes

To prevent rust in the under the hood of your car, ensure your drain holes are clean at the door bottoms and rocket panels.

This prevents water from accumulating in that area which could cause rust. Minivans and buses are particularly guilty of this, therefore use pipe cleaner to clear the holes.

Check for water leaks

It is important you regularly check the car fenders and liners for any water leakage. Look under the trunk and cargo areas for any signs that water is seeping.

Change paint chips and Dings

When damaged stone chips and car digs are not repaired on your time, they can create rust spots which can be dangerous. The best thing is getting some matching paints immediately, scratches are noticed to cover them.

Under the hood treatment

Since rust can form in car areas where we can’t see them quickly, giving your car underbody treatment regularly will prevent rust.

There are some underbody sealant car care which can be done to your car undercarriage and under the hood parts.


Rust and corrosion takes place in car parts and under the hood which many car owners aren’t aware of. Knowing what rust under the hood means helps you to know how to prevent and remove rust when it eventually happens.

Preventing your under the hood car parts from rust is easy when you steam regularly, check leaky holes and reduce exposure to water and salt.

It is better to remove rust during the surface rust stage using sandpaper, brush and tape, than when it gets to penetrative rust

Evan Cooper

Evan Cooper

Hi, I’m Evan Cooper, the founder and an editor of this site, Doesitrust. I’m a chemical engineer and working in a rust-eliminating paint manufacturing company. Besides this profession, I’m a researcher and blogger.

More Posts - Website

Leave a Comment