I would want to know what the coating is. Presumably Dinitrol or Waxoyl?

As the car is already having MoTs it is clearly a few years old. I've never bothered with rust protection, and I have always thought that applying it to a no-longer-new car was shutting the stable door. If the car is prone to rust it will have already started, so unless your treatment is very thorough in removing all trace of corrosion, you will be covering it up and no longer able to see what is happening underneath.

When I sold my 1990 Pug 205 a couple of years ago, the new owner thought about protecting the underside, which was in surprisingly good order after 30 years. He didn't, because the annual MoT is a good opportunity to check that is still the case.

At this age I think it makes more sense to keep the underside clear of winter accumulations.

Edited by Andrew-T on 09/09/2021 at 18:42

I've used all sorts over the years to rust proof having restored a few cars.

Less successful has always been underseal as it seems to kind of encourage rust tracking under the surface and you can't see the trouble brewing until it's a major problem.

Waxoyl as default didn't soak in properly inside sections although I had success by mixing waxoyl / clean engine oil.

These days I'm a fan on Dinitrol inside sections/cavities and Owatrol oil on exposed body/metal inc suspension parts - excellent rust inhibiting and it set to a transparent "resin" type finish so it's easy to keep an eye on things.

Edited by Big John on 10/09/2021 at 09:45

The Doctor is right, the Mk2 and even more so the Mk 2.5 with the 'laminated' front box sections is a rust bucket, and many of them look pristine from the top even at 20 years old, except for the odd blister on the rear arches or sills. In fairness these cars are now pretty old (1998-2005?) although Mazda don't seem to worry much about rust protection even now.

If you happen to have a truly rust-free (relatively) example then it would be well worth preserving but it is pretty certain that the sills are rusted from the inside unless it has been a garaged fair weather car all its life or well protected early on.(the vast majority out there have already been repaired, often badly).

You do have the option of partial or full restoration and preservation of course, which is not in my view a silly thing to consider if you have a mechanically excellent and tidy car that you really like - I say that because it is not usually financially a great idea, although prices are stupidly high right now if you wanted to buy a 'good' one - assuming you could find it for sale.

Hard to say without knowing your car, but the chances are that a good tidy up and dealing with the rust that's there would be the best place to start rather than just covering it over.

One of the best is themx5restorer.co.uk/ who did the rust prevention on my Mk4 when it was 6 months old in 2017. They use Dinitrol products and they wanted my car for a week. Nobody can do it satisfactorily in a day IMO especially on an old car with existing corrosion. If it needs cleaning off, it needs time to dry as does the material they use and at the very least I think yours would need some rust removing and treating before coating. Mine was easy because it was like new so they used clear wax and four years on there is no sign of rust and of course they did the critical cavities. I'm sure you could have a sensible discussion with them on the practical options for your car.

I'm not actually very near them - I got a cheap APEX return rail ticket from Pevensey & Westham, about 300 yds from them, took the car on Monday and picked it up Saturday. They know everything about MX-5's and do a lot of full restorations.

I had a Mk2 from 2011-2017 but it was a bit of a dog. In 2017 I decided to buy a better Mk2 but when I realised how many I might have to look at, I gave in and bought a much newer car - I think it's fair to say there was a lot of project creep, although I haven't regretted it. But I love the Mk2.

Edited by Manatee on 10/09/2021 at 13:42