MX-5 Miata Rust: The Ultimate Guide

Welcome to the ultimate guide to Mazda MX-5 Miata rust. I was inspired to write this guide based on my own experience and that of my friends in the MX-5 community.

This is a go-to guide to help you tackle rust on your model of MX-5 Miata.

With knowledge and prevention, you can stop rust in its tracks and fix the issue before it becomes too late.

To jump straight to the common rust issues for your MX-5 Miata model, select your model below:

What Is Rust?

Rust is the result of iron reacting with oxygen and water molecules. It is an iron oxide that creates a reddish-brown appearance on metals like steel and iron.

If left to worsen, rust can severely weaken the structural integrity of your vehicle. For that reason, it’s important to address rust issues as early as possible.

In this guide, we’ll fill you in on EVERYTHING you need to know about the common (and not-so-common) rust issues that affect every generation of the Mazda MX-5 Miata.

Are MX-5 Miata’s prone to rust?

The Mazda MX-5 Miata is notorious for its rust issues. It is likely caused by poor design decisions and ineffective rust-proofing techniques employed by Mazda in the MX-5 Miata’s production.

Mazda’s vehicles, including the MX-5 Miata, are well-known for their mechanical reliability. However, countless owners have been fighting a losing battle with rust on their vehicles.

NA MX-5 Miata – Rust Problem Areas

The NA MX-5 Miata was introduced in 1989 to an unprecedented reception amongst car enthusiasts across the world.

It reminded us of the British roadsters of the past – fast, freeing and non-complex. It was a refreshing experience that put the focus back on the relationship between driver and vehicle.

As with any car, it had its issues. Some of these issues didn’t make themselves known until many years after purchase, like rust.

If you own an NA, or you’re looking to own an NA, check out our list of rust problem areas below – how you can prevent them, how you can diagnose them and how you can fix them. 

1. Rocker Panels / Sills

According to our research, the rocker panel (or sill) area of the NA MX-5 Miata is the most common problem area for rust among its owners.

The exterior rocker panel drains of the NA can easily become blocked, which prevents water from escaping from the inner sill area. Also, the soft top drain holes can become blocked and encourage water ingress into the cabin and inner sills.

Because of the way that the rocker panels are designed, they will rust from the inside out. If you are seeing rust on the external paintwork of your rockers, it is likely that both the inner and outer sills have been affected by rust.

How to diagnose it: If the exterior of your rockers looks rusty, or the paint is blistered and bubbly, it’s likely that they are rusting from the inside out. If you can hear water sloshing when you drive, or your footwells are damp, water is trapped inside of your sills. Sitting water in your sills will eventually cause them to rust out.

How to prevent it: Remove the front wheel arch liners of your NA to remove dirt and debris from the front inner sill area. If your roof exit drains are blocked, use a trombone cleaner (Trombone Pipe Cleaner on Amazon) to unblock them (how-to). Make sure that your sill exit drains are free and able to drain water. If they are blocked up, clear them with a scalpel. If they are sealed completely, use a small drill to open them up.

How to fix it: Restoring your NA to a rust-free example will require fresh new metal welding into your sill area. You can buy pre-shaped metal units for this exact purpose. As the rocker panels/sills are a structural area of your NA, you don’t want to use filler of fibreglass. Such methods can weaken your vehicle and will only hide the rust.

2. Wheel Arches

When the rocker panel or sill area is affected, the rear wheel arches are usually not far behind.

The inner wheel arch lips of the MX-5 Miata NA are curved. When driving, water and mud can be kicked up into this area from your tires.

If left for too long, wet mud can sit against the inside of your wheel arches and rust them from the inside outwards.

How to diagnose it: Run your fingertips along the inside of your rear wheel arch lips. If you can feel dirt or grime, remove it. If the metal feels flaky or uneven, it is already falling victim to rust. To check the inner sections of your front wheel arches, you must remove the inner front wheel arch liner. If the external paintwork on your wheel arches is bubbling or blistering, it is likely rusting from the inside out.

How to prevent it: Make it a habit to clean the inside of your wheel arches on a regular basis. Remove dirt from the inner lip with a brush or mitt and spray with a hose or pressure washer to clean the area. You can also rust-proof your inner wheel arches with a suitable underseal spray. This can help to repel water and protect the metal.

How to fix it: If the rust has become an eyesore, or you can poke holes in it, it’s time to replace the wheel arch with fresh metal. As this is a common issue for NA MX-5 Miatas, you can buy readily shaped arches. This should be carried out by a professional welder, who can repaint and reseal the metal to deter rust in future.

3. Floor pan rust

The metal floor is located underneath the interior carpet in your NA MX-5 Miata. To access it, you can remove the seats and the centre console before finally unclipping the carpet from each footwell.

How to diagnose it: After removing the interior carpet, visually inspect the condition of the floor. Does it look rusty? Are there holes in it? You can also check the condition of the floor from underneath the vehicle. If you can see into the cabin from underneath your NA, you’ve definitely got a floor rust problem.

How to prevent it: Ensure that your soft top drain holes are unblocked so that water doesn’t enter your cabin. You can use a trombone cleaner (like this one) to clear the holes and allow water to drain outside of the car (how-to). If you have a roof leak, consider repairing or replacing the top. It’s also a good idea to check that your window seals are all working properly and keeping water out of your vehicle.

How to fix it: If it’s just surface rust, you can clean the area with a wire brush and reseal it. If your floor is severely weakened, you guessed it – this is a job for fresh metal. You’ll want to cut out any rusted metal and weld in fresh new metal. Once welded in, you can repaint and reseal the undercarriage of your vehicle to keep it rust-free for years to come.

4. The Undercarriage

It is fairly common to find surface rust on the undercarriage of your NA MX-5 Miata. This is due to Mazda’s poor rust-proofing techniques from the factory.

Whether it’s rust on the frame rails or rust on your suspension components, allowing it to progress can cause significant damage to your car further down the line.

How to diagnose it: Jack up your MX-5 Miata and secure it with axle stands. Alternatively, you can use a lift for this. Visually inspect the underside of your NA with a torch. Are there any areas that appear particularly rusty? If you poke it with a screwdriver, does it feel soft? You should then repeat this process with your suspension components, like the wishbones and control arms.

How to prevent it: Because Mazda did such a bad job of rust-proofing the MX-5 Miata, it’s a good idea to renew the underseal on your vehicle. First, you need to clean and remove any rust with a wire brush. Once any bare metal is repainted, use a long-lasting underseal product (like Dinitrol, available on Amazon) to coat and protect your undercarriage for years to come.

How to fix it: In classic MX-5 Miata fashion, you’ll need to replace severely rusted areas of your undercarriage with fresh metal. It’s always a good idea to get a trusted professional to do a good job on the welding here. A low-effort repair will only hide the rust, and it will end up coming back.

5. Miscellaneous

There are a few less common areas that might attract rust on an NA MX-5 Miata.

This includes the windscreen A-pillars and visible metal within the engine bay. For the most part, these are cosmetic issues that don’t pose any real danger. It’s up to you whether you want to rust-proof them.

For many issues like this, the rust can easily be tackled with a wire brush, a rust convertor product and some colour-matched paint.

NB MX-5 Miata – Rust Problem Areas

The NB MX-5 Miata hit the road in 1998, promising a whole host of improvements over its predecessor.

Unfortunately, many of the design faults that plagued the NA were carried over to the NB. At this time, Mazda was not fully aware of the scale of the rust issues that would afflict the first NA.

If you own an NB, or you’re looking to own an NB, check out our list of rust problem areas below – how you can prevent them, how you can diagnose them and how you can fix them. 

1. Rocker Panels / Sills

Much like the first-generation NA, our research concluded that the rocker panel (or sill) area of the NB MX-5 Miata is the most common area for rust among owners.

The rocker panel areas remain a HUGE rust problem area for the second-generation MX-5 Miata. Yet again, it’s a case of water being unable to exit the vehicle properly through the sills.

If the roof drain holes or sill exit drains are blocked with grime and debris, water will collect and sit inside of the sills. Eventually, this will rust the sills from the inside out.

How to diagnose it: If you can hear a ‘sloshing’ noise when driving or stopping, you might have water sitting inside of your rocker panels. If the exterior paint on your rockers appears blistered or wavy, it could already be falling victim to rust. If there is evidence of surface rust on your rocker panels, it is likely that they are already rusting from the inside out.

How to prevent it: Use a trombone pipe cleaner (Trombone Pipe Cleaner on Amazon) to clean your soft top roof drain holes on a regular basis (how-to). Remove the wheel arch liner covering your front sills and remove collected dirt and debris. Make sure that your sill exit drains are free and able to drain water. If they are blocked up, clear them with a scalpel. If they are sealed completely, use a small drill to open them up.

How to fix it: There’s really no other option but to replace the rusted metal with fresh new metal that can be welded in. Your rocker panels/sills are an important structural area of your MX-5 Miata. For this reason, you shouldn’t be using filler or fibreglass as a temporary fix. Using filler or fibreglass can weaken the car in the event of a collision.

2. Wheel Arches

The front and rear wheel arches are another common problem area for rust on the NB MX-5 Miata.

The issue here is mud, dirt and grime collecting in the inner wheel arch lips of the car. When the roads are wet, water and debris are kicked up by your tires into the wheel arch.

Dirty and wet mud being held against your inner arches 24/7 is never a good thing.

How to diagnose it: Run your fingertips along the inner rear wheel arch of your NB. If there is an accumulation of dirt, remove it. If you can feel flakes of metal or paint bubbling on the inside lip of the arch, rust has set in. To check your front wheel arches you must remove the inner wheel arch liner first. If there is visible paint bubbling or surface rust on the exterior of your wheel arches, it is likely that they are rusting from the inside out.

How to prevent it: Make sure to clean the inside of your wheel arches on a regular basis. Remove dirt from the inner lip with a brush or mitt and spray with a hose or pressure washer. We would also recommend rust-proofing your wheel arches with an appropriate underseal. This will repel water and protect the metal.

How to fix it: If the rust on your wheel arches is too far gone, there is no other option than to replace it with new metal. This should only be carried out by an experienced welder. It will be a case of grinding away rusted metal, preparing the metal for welding and welding in fresh metal. The new metal should be sealed and painted to ensure that it will be rust-free for years to come.

3. Front Chassis Rails

The front chassis rails are located within the engine bay. You can identify them as the two vertical bars running parallel alongside your engine.

When Mazda designed the NB, they decided to implement double-layered metal in the chassis rails to improve crash safety.

However, this new design traps water between the two layers of sheet metal. As the water cannot escape, the chassis rail metal will rust from the inside out.

This is a serious threat to the structural integrity of the MX-5 Miata NB. In the event of a front-end crash, the front chassis rails are supposed to protect you. It also acts as a mounting point for the anti-roll bar.

Rusty Front Chassis Rail on an NB (2nd Generation) Mazda MX-5 Miata
A particularly nasty case of front chassis rail rust on my Mazda MX-5 Miata NB.

How to diagnose: Open your hood and inspect the inside of your engine bay. Visually check the chassis rails. Do they appear to be rusty? Run your hand under the chassis rails. If the metal feels uneven or blown out, your chassis rails are toast.

How to prevent it: There is no real way to prevent front chassis rail rust on an NB MX-5 Miata. If you live in a warm climate, you might be able to avoid it. But if you live in cold and wet climates, it’s a question of when, not if.

How to fix it: The metal needs to be cut out and replaced with a single sheet of metal to prevent a recurrence. Pre-shaped metal is readily available to purchase for this exact requirement. We would recommend hiring an experienced welder to carry this out. Once the new metal is welded in, it should be re-painted and sealed to inhibit rust.

4. Battery Tray

The battery tray is located in the trunk of an MX-5 Miata NB. To access it, you must pull up the carpet and remove the corkboard that protects your spare wheel.

Sometimes water can be ingressed through ineffective seals in the rear light units. This water ends up in the battery tray, where it has nowhere to escape.

Over time, this water can severely weaken the metal that houses your car battery.

How to diagnose: Open the trunk and remove the carpet and the protective corkboard. Shine a torch into your battery tray. Is there sitting water? Does the metal appear rusty? You can also take a look at the underside of the tray. If the metal appears weakened or already has holes, your battery tray has rusted out.

How to prevent: Check your battery tray on a regular basis for water ingress. If water is collecting in your battery tray, remove the battery and extract the water with a turkey baster. If water is coming in through your rear light units, consider replacing the sealing or the unit itself.

How to fix it: This is becoming a common theme, but there is no other option than to replace the battery tray with fresh metal. As this is a common issue, there are pre-shaped metal kits that are the perfect fit. It’s best to trust a qualified welder to complete this job. Repaint and reseal the metal once finished.

5. The Undercarriage

Ineffective rust-proofing from the factory meant that many MX-5 Miata NB’s have fallen victim to rust on the underside of the vehicle.

Whether it’s on the frame rails or the suspension components, rust can weaken the frame of the car as well as its vital suspension components.

How to diagnose it: Visually check the underside of your car with a torch. You will want to use a lift or a trusted trolley jack and axle stands to do this. Do any areas appear to be extremely rusted? If you’re unsure, try poking the metal with a screwdriver. If it feels soft or caves in easily, this metal will need replacing. Repeat the same process with your suspension components, like the wishbones and control arms.

How to prevent it: We would recommend fully cleaning and resealing the underside of your NB. If you’re unsure, or you lack professional equipment, get a qualified professional to do this. Strip back the factory underseal and clean away any surface rust with a wire brush. Once the underside is cleaned and rust-free, repaint it and reseal it with a tough underseal spray (like Dinitrol).

How to fix it: If the metal on your underside is too weak (or holey), it will need to be replaced with fresh metal. It’s rare that the entire floor of the vehicle needs to be replaced – just smaller sections. It’s best to get a professional to do this. Once the new metal is welded in, protect your undercarriage with a fresh lick of paint and some underseal.

6. Miscellaneous

You know what they say – it’s not an MX-5 unless it has some rust on it.

A few other less common areas for rust on the MX-5 Miata NB include the windscreen A-pillars and metal within the engine bay. Such issues are mostly cosmetic and don’t pose an immediate danger.

They can be tackled with a wire brush, a rust convertor product and some colour-matched paint.

NC MX-5 Miata – Rust Problem Areas

The NC MX-5 Miata was introduced in 2005 and produced until 2015. It is the longest of the Mazda MX-5 Miata production cycles.

By this time, it was becoming apparent to Mazda that older models of the MX-5 Miata were suffering from rust-related issues.

Although rust is not as common in the NC, it can still happen in cold and wet climates.

If you own an NC, or you’re looking to own an NC, check out our list of rust problem areas below – how you can prevent them, how you can diagnose them and how you can fix them.

1. Rocker Panels / Sills

Much like its predecessors, our research found that the rocker panel (or sill) area of the NC MX-5 Miata continues to be the most common rust area among owners.

You would be forgiven for thinking that Mazda might have fixed this issue after the first two generations of the MX-5 Miata.

The rocker panels, or sills, continue to be the most common problem area for rust on the NC MX-5 Miata – especially the sill end panels.

How to diagnose: Visually check the exterior rocker panels (or sills) of your NC MX-5 Miata. Are they showing signs of rust? Rocker rust on the NC is very common in the sill end plates, which are located in your rear wheel arch. To inspect the sill end plate, you’ll need to remove the matting that covers the area and take a look inside the rocker panels. As always, if rust is evident on the outside, you can guarantee that the inside will be worse.

How to prevent it: Clean your NC from top to bottom on a regular basis. Pay particular attention to the sill areas. To remove dirt build-up, you will need to remove the matting that covers the sill endplate in your rear wheel arches. You should also purchase a trombone cleaner (like this one) to clean your hood drains and prevent clogging due to dirt (how-to).

How to fix it: If your sills are deemed to be structurally weakened by rust, it’s time to get them repaired. This will involve welding in new metal and eliminating all of the existing rust to ensure your NC is good for many years to come. We would recommend getting an experienced welder to do this, which should prevent any rust-based heartache in future.

2. Wheel Arches

Wheel arch rust is a problem for many vehicles, and not just the MX-5 Miata NC.

Cavities in your wheel arches are prone to catching wet mud and grime from road driving because the tires kick up dirt into that area.

How to diagnose it: Conduct an in-depth, visual check of the four wheel arches around your NC. Is there any visible rust? Does the metal still feel solid? A common problem area for NCs is the rear wheel arches. Mud and water can get trapped in the seams between the inner and outer wheel arch area, where they are spot-welded. Run your finger along the lip of your wheel arches (towards the rear bumper) and check that the metal is smooth and not lumpy. If this area feels jagged or flaky, you’ve got rear wheel arch rust.

How to prevent it: The gap between the inner and outer wheel arch metal is a design fault on Mazda’s part. In that sense, there’s not much you can really do to prevent that. In the meantime, keep your wheel arches fresh with a regular clean. Brush away dirt, apply a degreaser and spray your wheel arches with a hose or pressure washer to stop wet dirt eating away at your metal.

How to fix it: Surface level rust would only require a wire brush, some rust converter and reapplication of paint and underseal. If your wheel arch metal is severely weakened, or even holey, this will require a welding repair to keep your NC roadworthy. Take it to a specialist to ensure a perfect job from start to finish.

3. Rear Bumper Mounts

This one can be easy to miss. Ineffective anti-corrosion treatment (or poor quality metal) from the factory can lead to significant rust on the rear bumper mounts of the third-generation MX-5 Miata.

In the event of a rear-end collision, you don’t want weakened metal protecting you and your passengers.

How to diagnose: For this one, you’ll need to take off the rear bumper (how-to). Remove the rear light units and the rear wheel arch liners and then remove the pop rivets and screws that fix the bumper into place. Then, you can remove the rear bumper support structure. Once removed, the extent of the rust should become clear.

How to prevent it: The only way to prevent this from happening is to catch it early on and re-apply some rust protection. Follow the steps above, and clean the mounting area and support structure with a wire brush and degreaser. Once cleaned, apply high-quality paint (like Hammerite, available on Amazon) to both the mounting points and the bumper support structure. This will help to protect the rear-end for the future.

How to fix it: If the metal is too weak, or holey, it will need to be replaced with fresh new metal. Consult an experienced welder or an MX-5 Miata specialist if you don’t feel confident. If it’s just surface rust, don’t worry – follow our tips above to ensure it is protected for thousands more miles.

4. Floor Panels

For any convertible sports car, leaks are the enemy. This is especially true for the NC MX-5 Miata.

If water is allowed to collect under the interior carpet and rest against the floor panels, this could cause significant problems (and holes) further down the line.

How to diagnose: Remove the seats, interior trim and interior carpet from the vehicle. Inspect the metal floor below. Is it rusted, or severely weakened? This may be due to a leak. Is there an obvious leak coming from somewhere? Common areas include the soft top drain holes and the lower seals around the windscreen area. You should also check the condition of the soft top for holes or ineffective seals.

How to prevent it: Don’t let leaks go unfixed for too long. It’s a good idea to keep an eye on the condition of your soft top and window seals. If you can keep the interior of your NC dry, you should avoid any significant floor panel rust.

How to fix it: If there is a small amount of surface rust on your floor panels, this can be easily fixed with a wire brush, rust convertor gel and some high-quality paint (like Hammerite, available on Amazon). If the metal is severely weakened or you can poke holes in it, it’s time to get the experts in. Unless you’re already a welder, of course. The metal will need to be replaced and re-sealed with fresh metal and anti-rust protection.

5. Undercarriage

Ineffective rust proofing from the factory means that NC MX-5 Miatas are susceptible to rust on the undercarriage.

This includes the frame, floor, subframes and suspension components. Significant rust here can weaken the frame of the vehicle and its core suspension components.

How to diagnose: Use a trusty jack and axle stands to lift the car. Alternatively, if you have access to a lift, use it. Use a torch to visually check the undercarriage of your NC. Investigate the suspension components, like the springs, wishbones and control arms. Are there areas that appear particularly rusty? Can you poke holes in the metal? If so, you’ve got some serious undercarriage rust on your hands.

How to prevent: If you live in a wet, damp area that uses salt on the road in the winter, you should clean the undercarriage of your NC on a regular basis. Use a pressure washer and some degreaser to blast out dirt and grime from hidden cavities. If you want to go one step further, consider re-applying underseal to prevent rust from forming. Before applying underseal, make sure any surface rust is dealt with to ensure a nice clean surface to apply against.

How to fix: For surface rust, clean the area with a wire brush and anti-rust convertor. You can also take rusty suspension components in for sandblasting and re-painting, which will eliminate any rust. If your metal is severely weakened or has holes in it, it’s time to replace it. For suspension components, see if you can buy used parts. For undercarriage metal, it’s best to get an expert to weld in fresh metal and rustproof the underside for peace of mind.

6. Miscellaneous 

Occasionally, less-common areas of rust on the NC MX-5 Miata are flagged up by owners.

This can include rust on the trunk lid, windscreen A-pillars and at the top of either side door where the window sits.

For the most part, they are simply cosmetic issues. It’s up to you whether you’d like to clean them up and improve the appearance of your car.

To do so, use a wire brush and a suitable rust converter product. Once the rust has been eliminated, re-paint the area with colour-matched paint, and you’re good to go.

Does the ND MX-5 Miata have rust issues?

At the time of writing, there are no widespread rust issues with the ND MX-5 Miata. We have conducted extensive owner and forum research, where we couldn’t find evidence of a common rust-induced problem with the vehicle.

As with any car, if you live in a wet, cold climate with salt on the roads: it’s a good idea to get regular rust protection applied to your ND.

This can include cavity wax, underseal application and regular cleaning of the vehicle’s undercarriage.

Remember – prevention is key when it comes to rust. Practice preventative maintenance and your car should be road-ready for many years to come.

Conclusion

And there you have it. I’m a huge fan of the Mazda MX-5 Miata. I’ve always wanted to own one.

I had heard of the significant rust issues that plagued the younger models, but I never imagined it could be THAT bad. After owning an NB for several years, the true extent of the issue has become clear.

A mixture of poor quality metal and poor anti-rust protection from the factory is likely the cause of these issues. Furthermore, leaving bare metal scratches (i.e, from vandalism) encourages rust to form at a rapid rate.

Yet for the enthusiasts, rust is not enough to stop them from enjoying their MX-5 Miatas.

If the car is worth it to you, we would recommend repairing any rust you have and keeping it on the road. They are super reliable in every other sense – it’s just rust that lets it down.

Did we miss anything? Let us know!

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