How much does it cost to repair a Mazda MX5 sill?

Mazda MX-5s are loved for their light weight, sharp handling and reliability, but sill corrosion is a well-known weak point, particularly on older models.

Because the sills form part of the car’s structural strength, issues can affect safety, MOT results and long-term value. The average MX-5 sill repair costs range widely between £80 and £1,200.

Here’s everything you need to know about repairing MX5 sill damage.

How much does it cost to repair sills on an MX-5?

The cost of repairing MX-5 sills in the UK typically ranges from £80 to £1,200+, depending on the extent of corrosion.

Minimal surface rust can often be treated relatively cheaply, but once corrosion spreads inside the sill cavity or reaches the inner structure, repairs become labour-intensive and costly.

Many MX-5 sill repairs involve cutting out corroded metal and welding in new steel sections, which significantly increases labour time.

As a general rule, early intervention keeps costs manageable, while delayed repairs often require partial or full sill replacement. You can use car repair finance to split any MX5 repair costs into interest-free repayments.

Typical MX-5 sill repair costs by damage severity

MX-5 sill repair costs vary depending on how far corrosion has progressed and whether inner structural sections are affected.

You should also remember that prices vary depending on the MX-5 model year, labour rates, and the extent of internal sill corrosion discovered during repair. Keep this in mind when booking your service!

Below is a general guide to what owners can expect to pay in the UK in 2026.

Why do MX-5 sills rust so badly?

MX-5 sill corrosion is largely down to design and drainage issues. Water enters the sill cavity through the hood drain channels and, over time, becomes trapped inside.

Combined with road salt and moisture, this creates the perfect environment for rust to develop from the inside out. Because corrosion often starts internally, the outer sill can look fine until significant structural damage has already occurred.

Which Mazda MX-5 models are most affected by sill rust?

All Mazda models can experience sill issues, but sill corrosion is most common on:

• Mk1 (NA) MX-5

• Mk2 and Mk2.5 (NB)

These models are particularly vulnerable due to less effective rust protection and drainage design.

Later NC and ND models are generally better protected, but they’re not immune, especially if drainage channels are blocked or maintenance has been neglected.

How long does MX-5 sill repair take?

Mazda MX5 sill repair times depend on severity. You divide the three main types of sill repair into the following categories:

• Minor surface repair: 1 to 2 days

• Welded sill sections: 2 to 4 days

• Full inner and outer sill replacement: 4 to 7 days

Paint curing and corrosion protection treatments can extend repair times, but these steps are essential for long-term durability. Your garage will let you know if your Mazda requires any additional work.

Is sill rust an MOT failure on an MX-5?

Yes. Sill rust can cause an MOT failure if it affects structural areas.

MOT testers pay close attention to corrosion within 30cm of seatbelt mounts, suspension components and jacking points. Any perforation or weakened metal in these areas is likely to result in a failure.

Even if the car passes with advisories, repairs shouldn’t be delayed, or you might risk expensive repairs.

Can you drive an MX-5 with rusty sills?

Technically, yes, but it’s best not to.

Light surface rust isn’t immediately dangerous, but once corrosion becomes structural, driving the car poses safety risks.

Weakened sills reduce crash protection and compromise chassis integrity. Continued driving also allows corrosion to spread further into the sill cavity, significantly increasing repair costs.

Is it worth repairing sills on an MX-5?

In most cases, yes. MX-5s hold their value well, especially clean, rust-free examples.

It’s worth repairing sills because repairs:

• Preserve structural integrity

• Protect resale value

• Prevent MOT failures

• Are often cheaper than replacing the car

For enthusiasts and long-term owners, sill repair is usually a worthwhile investment.

Can MX-5 sill rust spread if left untreated?

Absolutely. Rust spreads quickly inside sill cavities, often unseen before it becomes a major problem.

A little £200 surface repair can escalate into a £1,000+ structural rebuild if ignored. Once inner sills rot through, repairs become more complex and costly.

Is the Mazda MX-5 cheap to maintain?

Overall, yes. MX-5s are generally affordable to maintain compared to many sports cars.

Routine servicing, brake, and suspension repairs are reasonably priced. However, rust repairs (especially sills) are among the few areas where costs can spike if problems are left unresolved.

What’s the most common problem with the Mazda MX-5?

Across generations, the most commonly reported MX-5 issues include:

• Sill and arch corrosion

• Hood drain blockages

• Suspension bush wear

• Age-related rubber seal deterioration

Of these, sill rust is usually the most expensive if ignored. This is your sign to get your Mazda serviced soon!

Final thoughts

MX-5 sill repairs can range from affordable to expensive, depending entirely on how early corrosion is caught. If you suspect sill rust, a professional inspection is the best first step. Acting early keeps costs down and helps your MX-5 stay enjoyable for years to come.

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