I have a 2020 MX-5 (fingers crossed!)

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Crossing fingers is the cheap option but probably ineffective. Seriously, treat the MX-5 now. Many are relatively low miles so are killed by rust, or fortunes are spent fixing them.

I had mine (2017) treated when I bought it at 6 months old, by The MX-5 Restorer at Pevensey in East Sussex. They know where to put the jollop, they do rust repairs every day, As it was like new underneath they used clear wax rather than the black stuff so it can be seen to be corrosion-free. I intend to keep it anyway but given the reputation of MX-5's for rust, I think it would be a plus were I to sell privately too.

Edited by Manatee on 08/10/2021 at 17:52

When I took my 03 Forester in for an MOT this year I asked the tester if I should be thinking about getting rid as the car was 18 years old.

He said there was some light surface rust on the sub frame but nothing to worry about. He said if i bought a new car it probably wouldn't last as long as the Forester will.

I have never done any rustproofing, just jet washed under the arches etc each spring.

I have a 2012 Mazda 6, and the rear subframe components were rusty when the car was delivered brand new. Mazda's customer services were completely unhelpful, and it was only when I threatened to reject the car that the dealer arranged for a body shop to clean and coat the rusty spots. However in the intervening years the car has developed a number of rusty spots underneath, probably not helped by a few salty winters. I've not had an advisory on that, yet.

ALL cars rust - the average life of a car in the UK is c 12 years. If you want longevity, look after the bodywork underneath.

In absolute terms, yes, all cars rust. But my Pugs 207 (2008) and 306 (1994) have had one trivial advisory each for surface corrosion, which have not reappeared on later tests, without any treatment.

So some makers found effective methods of rust prevention many years ago. Others have found ways to cut corners in that treatment, perhaps with the results you describe.

Anyone with any Mercedes built between c 1995 and 2005 will have a detailed personal knowledge of rust from after the car was about 3 years old.

It'll be interesting to see how the latest Mazdas fair, as they appear to have been a significant improvement in the fit and finish quality, as I believe they intend to go 'up market'. Hopefully this will prove to extend to the rust proofing and other niggly issues certain models or ones with certain engines have had over the years.

To be fair with the MX-5 mkIII, it was around for nigh on 10 years, which is a long time for a model to be out, just around the time when money was tight for them during the economic woes of 2008 and the subsequent divporce from Ford.

Have you heard of any issues with later MkIIIs or the mkIV from 2015 onwards? Most of the issues for the latest Mazda3 on the owners' forum tend to be to do with (as is the case with many modern cars) faulty electronics on one of the many gizmos they now have.

One thing also that was mentioned was people treating the underbody when they buy new, but I seem to remember being told that it isn't always possible for all areas because some need to be inspected for the service/MOT and occasionally adjusted or opened for maintenance. Does it affect the warranty?

I must admit thinking about getting it done for my next car (given I tend to keep mine a long time) - if it's worth it.

A friend does have a very tidy 10yr old example which looks completely rust free on top, I may take a wee peek under it at some point. I hold onto hope that the new model won’t suffer this but again I kinda hoped this with the Mk III.

A friend bought a 2012 Sport Black a couple of years ago, rust-free despite being from Torquay! But he had looked at at least a couple that were completely brown underneath.

So far the Mk4 seems OK, there are large areas with no obvious sign of special protection but they don't seem to be rusting there - the oldest cars are MY 2015. But as we know, the Mk2's rusted from the inside out, in the sills, rear arches and the 'laminated' front chassis rails. I decided I'd get my retaliation in first and put it in for some protection. It was a bit under £400 I think, and certainly cheaper than typical rust repairs, although there is no guarantee that it will never rust.

I'm sure you're right about the importance of the car being dry before treatment. Any but a very new car will also need washing off and drying out. Despite this many "rustproofers" only want the car for a day. Just possible I suppose to do it properly if dried with a lot of heat but I wasn't convinced. The jollop is fairly tacky and smelly for a while as well and is probably better allowed to dry. The people I used wanted it for a week. I bought a return train ticket, left it on a Monday and picked it up on Saturday morning.

I would agree that a converter like Owatrol is a good approach if I was doing it myself. I am under no illusions that what my garage is doing is, at best, only going to hold it for a year or two. However they use this Schutz stuff all the time and, having sought their advice, I will stick with it.
I will also check with him once he has wire brushed it and done the work as to how far the corrosion has gone. Even if he gives it a clean bill of health for now, no liquid or underseal will restore lost strength. Once rust is present I reckon it’s just a question of time before it comes back here or somewhere else in the car.

For many years I occasionally applied old engine oil with an old toothbrush to the springs and subframes of our Focus. It failed the MoT for rust the first time at 16yrs old and the next time at 18yrs old, both due to corrosion tracking under the 'protection' (ha!) on the sill area by the rear wheels. The subframes have also had an occasional coat of Hammerite. In December it will become of age at 21 yrs old, and might be allowed a drink of fresh 5W-30.