interesting video if you haven’t seen it Mazda being built at the factory including the Nd MK4 clearly shows the body being dipped I take it that’s some sort of rust proofing. if you want to see it go on you tube and search frame Mazda
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My search engine must be rubbish, as I drew a blank.
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yes that’s it
The process you see is rust preventing not rust proofing. Its pretty much the same process going back to the NA, except the paint is now water based.
ND MX5s won’t rust until suddenly they do
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Mind you, regarding that pic, that’s not bad for a daily driven car. I’d wager hundred of thousands of cars would look like that- or worse- in the UK if you jacked them up. Millions even if there’s apparently about 34 million registered on UK roads.
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I recall on the predecessor to the forum, the “List”, around about 2001-2002, about whether NAs were prone to rust. The consensus was they were really good compared to (then) 10 year old Fords and Vauxhalls. The rest is history.
All MX5s will be prone to rusting. Its not rust from the outside that kills any of these. Its rot from sill sections, and thats all because these are convertible. On a tin top, rain water flows over the body. On a convertible, its purposely directed to the internal structures, through a series of drains, passing through areas already more complex than a tin top. Drains can fail, condensation starts, and rust occurs.
On NAs, the only time I have heard floors to rust out is because of a leak that gets under the rubber backed carpets. All this undersealing; waste of time. MX5s don’t rust like a Mk3 Cortina or Maxi… The electropriming is very effective; you can ding or scratch the paint to the metal, and the car doesn’t suddenly break out with rust acne.
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Good points and explanation.
If you ALWAYS use a half cover, so nothing on the top gets wet, would it then be spared the same fate?
Most half covers are semi-universal, with bits of cover and various straps, and so have a tendency to lightly scratch the paintwork.
Additionally, they are shower proof, not water proof, ie things like the seams are not sealed. Water will track under the cover. It will certainly reduce the volume though.
They are of most use in cars with leaky tops, usually NAs/ NBs. Also they protect the hoods from UV damage. The Mohair tops are obviously not mohair. They are an out canvas type material (usually nylon) bonded to a rubber layer. Over the years, the rubber rots, due to UV, and thus reproofing can extend the life a little.
Believe me, mine lets not a drop through (two covers on at once!). Wnen you’ve had 6 years of getting up at 3 am in storms just to check nothing’s come undone etc, airing it every day, ‘dog hair drying’ slight winter codo on metal parts, you know none gets through lol
So in essence a totally dry soft top (as well as not driving it in the rain) = nothing rusting inside out 
The top, if I say so myself, looks BETTER than anyone I’ve seen on a forecourt, even new, with those usually sitting there covered in tree bits. The half covers are worth a grand for what they’ve managed with mine in 6 years!
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Nearly 30 years and 4 covers, they all leak.
A half cover is not a geritol fix for not bothering to check drains are clear.
I can only go by my own six years totally OCD experience ensuring a totally dry top. You probably don’t understand the lengths I go to lol Totally dry
Yes, they do become a bit more saturated with time. I get a new one every year. And I use two of them at once.
Drains are mint. When it has an annual wash to check, the water drains in no time.
I kind of know what I’m doing on this score. Like I said, I’d love to compare my six year soft top to ANYONE’S! 
But rather than argue of the finer points of half covers etc if a top is dry = no rusting inside out. That’s all I was looking for
Condensate will still form inside the sill sections, cover or no cover. Those sills aren’t seals from the rest of the body. A damp boot (eg leaking boot seal, cluster seal) might still translate into sills rusting. In addition, you need to be on top of any chipping or failure of the seal between the outer wing and inner wing at the arch lip. Some rusting here will balloon the metal, allowing a route for really dirty, salty water direct into the sill.
When you see rust like this:
Did it rot out because the sill drains were blocked, allowing water to enter a non-draining are (which is the bit between the outer panel and the sill itself), or because it started to rust around the wing lip?
If the former, why aren’t the two panel pressing holes rusted?.
Sticking a hood cover does not ensure there is no possibility of rusting in the sills. And if you don’t drive in the rain, does that include not driving after it has been raining? There are, on average, 170 wet days a year in the UK. So 195 days when its not raining. But of those days, upto 85 days might have wet roads. Is it worth owning a MX5 in the UK if you avoid all wetness?
6 years is young for a MX5. Get to 10 years, then they start to go down hill. As I said, in 2000, received wisdom back then was MX5s don’t really rust.
One of my past cars was a former show car. The owner was fastidious. Fully nitrol’d, only taken to shows for the trophies. I acquired it 5 years after its showcar days were done, and the sill were shot then.
Most owners are unaware of a car being rusty, until it is. Those sills rust from the inside out. The very first sign is an apparent loosening of the paint; it appears like a soft bubble. You might even think its a paint defect. A little pin to the bubble will let out some clean looking water. You might even clean off the bubble of paint, and be mystified by the shiny non-rusty metal. But look closely, and you might see the tiny tiny pinhole. Going outwards, you might see a slight blackening of the metal, almost as an aura around the pinhole. That the edges of the big rust hole forming. If you pushed on the shiny metal, it will crunch.
To keep up with the OCD, you need to buy a boroscope to inspect the sill sections. But if you spot some crustiness, what do ou do… Not a lot at that point. Flood the sills with rust killer maybe, then wax, but then there is the risk of sink spots that accelerate the rusting.
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Or you could just not worry, drive it like you stole it, enjoy the hell out of it, and when it dissolves into a pile of rust on the drive say “Thanks for all the great memories” and buy another one. Life’s too short.
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Yes, I don’t drive when the floor’s wet either
And even worse, if salt’s been down, I wait until it’s been hammering down for days and days to wash away much of it. I probably give it a spin about every six weeks in the winter, again when conditions are as ‘ideal’ as they can be for winter roads (obviously nothing perfect). And you’ll like this one: I even ‘vet’ the roads, ‘tasting’ them after wetting a finger
You sound a bit like my Mrs with the ‘is it worth it’ argument lol
The answer is yes, and I’ve paid for it with my (well, ‘our’) money and I enjoy driving it when I do. I have other cars in the household, so I don’t have to rely on my ND as an every day car, and can drive it when I choose too.
That is a good argument in fairness.
Which is what I used to do. Though after 20 years with this one, 200k kms of me driving it, and 28 years with MX5s, my interest in the marque is now quickly evaporating. It has sat in the garage most of this year with a collapsed brake hose and lack of inertia. I’m getting to the end of this journey I think.
In 20 years, I have spent about £1700 combatting rust, and the repairs are getting on for 7 years old, with no sign of failure. I’m not sure what state the car would be now with £85 worth of garage chassis oiling a year; that doesn’t get you much (half an hour labour, and some slathering of tar on top of rust). I gather some people are suckered into £400 annual checks.
What I have noticed though, with a decline in use, is an increase in unreliability. The cars need to be used, and cars used sparingly, may need increased mechanical maintenance. Brake fluid absorbs moisture, seals dry out, petrol gums.
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I’m 73 and had a very close brush with the infinite last year so that might influence my viewpoint a bit 
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