I am about to purchase a new car having had 3 cars previous that all showed signs of rusting. Are the new cars any better rustproofed and is it worth while rust proofing a new car. The ND has now been out for 3 years and I would like any feedback from owners
thanks Alun Price
There are various threads on the forum about this, the short answer is that unfortunately the new cars are no better protected than older cars. Here’s one thread that may be useful:
If you’ll be keeping your new car for more than 5 years, then it’s definitely worth giving it a rustproofing treatment as soon as possible after you take delivery. When I bought my NC2 I was intending to keep it for 7 to 9 years, so I had it rustproofed as soon as I got it (new) & now that it’s 7.5 years old I’m really glad that I did!
On the other hand, if you won’t be keeping your new car for more than 5 years, I’d say that it isn’t worth it. Yes, it will be starting to rust by the time that you swap it but the rust will be underneath & not yet structural at that age. Anybody in the know about MX-5s would pay more for a 5 year old car which had been rustproofed from new, but if you were to just trade it in at a dealer then the part-exchange value would be the same regardless of whether rustproofed or not. All the benefit of your cash outlay would then effectively go to the 2nd, 3rd etc owners - instead of to yourself.
Reviving an old thread here. Long and short. Has a 2023 roadster received any sort of rustproofing from new at the factory? Cheers
^ epic thread bump 
It has some, but how much and if more is required (depending on how your car is used), others will advise.
One thing ND owners might like to check is their sills.-those pokey down bits which run along the underneath of the sides of the car, about 6 inches back. Get a small hand mirror and look behind them. My ND don’t see the rain (or salt) unless I’ve something like a service booked and it rains on the day, but in the first year I had it it was used a bit more as a ‘normal’ car, but still I was careful.- still even then trying to avoid rain and salt and often giving the underside a hose. Mine had some light rust along the back of the sills (like I said, ND users get a small mirror, get on the floor with the mirror and maybe a torch to shine on the mirror, and have a look, all the way along). I had them scraped and undersealed to be on the safe side, but still, every other car in the family don’t have it, and they don’t get as pampered as my ND has (and on 15K miles).
In short, not really. Parts of the underside panels have been sprayed with a flexible coating (possibly some kind of polyurethane at a guess) but the coverage is less than comprehensive. I think it’s primary purpose is soundproofing and protection from stones and other road debris that gets thrown up at the underside rather than rust protection. I spent most of the first week of ownership flat on my back under the car (on axle stands, I might add) rustproofing with Dinitrol ML followed by Dinitrol 4941. The front and rear subframes were already showing signs of rust on the welds so I sprayed both the inside and outside of the box sections with ML using a flexible lance and compressor. This was followed by the thicker 4941 on the outside. There is no rustproofing beneath the wheel arch liners whatsoever. I have to say it was a revolting job to do, the 4941 gets everywhere and is truly horrible sticky stuff, but I suppose that is why it is so effective!. I intend to keep the car long term so in retrospect I think it was worth it, even though it won’t be driven from November to April. The subframes could easily be galvanised after fabrication and it would probably only add about £300 to the price of a new car, well worth it IMHO.
In this day and age it really does surprise me that after all the rust issues with MX-5’s that for markets such as ours where it rains a lot they don’t rustproof them properly. Only other car in recent years that I have had without rustproofing was a 2012 Jaguar XK V8, but that was all made out of aluminum.