Rust and the MX-5 NC
The third-generation MX-5 generally resists corrosion better than the earlier NA and NB generations, but that doesn’t mean an NC should automatically be considered rust-free. As the earliest cars are now over 20 years old, corrosion is becoming increasingly relevant when buying one. Recent buying guides recommend checking the sills and subframe mounting areas in particular.
More importantly, don’t judge the condition of an NC purely by what you can see while standing next to it.
A car can have shiny paintwork, clean wheels and an immaculate interior while corrosion is developing underneath.
PROJECT MX5 ADVICE
When buying an NC, spend at least as much time looking underneath the car as you do looking at the bodywork.
Where should you check?
There are several areas worth inspecting carefully.
- Rear wheel arches and sill ends — look particularly closely where the bottom of the rear wheel arch meets the sill. Owners have reported corrosion developing on the inner side of this area, where it can be difficult to see without getting underneath the car.
- Rear chassis sections — corrosion has also been reported towards the rear ends of the chassis rails, sometimes where the factory protection has lifted or deteriorated.
- Underside and subframe mounting areas — surface corrosion is common on older cars, but pay closer attention to heavily scaled metal, weakened seams and corrosion around structural mounting points.
- Behind wheel-arch liners — dirt and moisture can sit in areas hidden by plastic liners, so the visible wheel arch doesn’t necessarily tell the whole story. Recent MX-5 Owners Club advice specifically highlights inspecting the lower rear arches behind the liner.
- Bonnet and boot edges — lighter cosmetic corrosion can appear where seals or trim have rubbed through paint. This is usually far less serious than structural corrosion underneath.
Surface rust or something more serious?
Not every patch of brown metal means you should walk away.
An older NC that’s been used year-round is likely to have some surface corrosion underneath. What matters is whether the corrosion remains superficial or has begun attacking the structure.
Light surface rust can generally be cleaned back, treated and protected.
More concerning signs include metal that is heavily flaking, swollen seams, holes, extensive previous welding or areas that feel structurally weak.
If you’re not confident telling the difference, a pre-purchase inspection on a ramp is money well spent.
Be cautious with fresh underseal
Underbody protection is a good thing when it’s applied correctly.
A car that has been properly cleaned, treated and protected can actually be more attractive than an untouched example.
The problem is that fresh black underseal can also make an unhealthy underside look remarkably tidy.
If a seller tells you the car has recently been rust-proofed, ask:
What preparation was done first?
Ideally there should be photographs or invoices showing that existing corrosion was cleaned and treated before the protective coating was applied.
Simply spraying coating over rust doesn’t remove the problem.
Check the roof drains too
Rust inspection isn’t confined to the outside of the car.
Blocked soft-top drains can allow water into the cabin. Damp carpets, moisture behind the seats or a persistent musty smell should therefore be investigated rather than dismissed as normal convertible behaviour.
Water ingress can also affect components beneath the carpets, so finding a leak early matters for more than simply keeping the interior dry.
Related guide → MX-5 NC Roof Drains & Water Leaks
Check the MOT history
Before travelling to see the car, enter its registration into the UK government’s MOT-history service.
Look particularly for repeated advisories involving:
corrosion, suspension mounting areas, brake pipes, subframes or structural components.
One old corrosion advisory doesn’t necessarily condemn a car — it may subsequently have been repaired properly.
Repeated advisories over several years without evidence of repair are considerably more interesting.
What about repaired cars?
Previous welding isn’t automatically bad.
On an ageing sports car, a properly repaired and protected section can actually be preferable to an untouched area that’s quietly deteriorating.
What matters is the quality of the repair.
Look for neat welding, sensible finishing and evidence that the repair extended back to sound metal rather than simply covering a hole.
Receipts and photographs from a recognised MX-5 specialist are useful evidence.
Should rust make you walk away?
That depends on what you’re buying.
If you’re deliberately looking for a cheap project, corrosion may simply be part of the calculation.
If you want a car to use immediately, serious structural corrosion should substantially change how you view the price — and sometimes whether you buy the car at all.
There are enough NCs available that you don’t need to convince yourself to buy a questionable one.
PROJECT MX5 RULE
Cosmetic imperfections are easy to live with. Structural rust isn’t.
The ideal inspection
The best way to inspect an NC is on a lift with someone who knows MX-5s.
Wheel-arch liners and undertrays can obscure areas you would ideally inspect, and Owners Club discussions repeatedly recommend getting underneath the car rather than relying on the view from above.
Even if you can’t arrange a professional inspection, take a torch and don’t be embarrassed about getting down on the ground.
You’re buying the metal underneath the shiny paint too.
Before you view the car
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